WO2024105985A1

WO2024105985A1 - Gas sensor chip, gas sensing system, and production method for gas sensor chip

Info

Publication number: WO2024105985A1
Application number: PCT/JP2023/032889
Authority: WO
Inventors: 佳孝笹子; 博幸内山; 渊卜; 崇泰乗松
Original assignee: 株式会社日立製作所
Priority date: 2022-11-14
Filing date: 2023-09-08
Publication date: 2024-05-23
Also published as: JP2024071185A

Abstract

According to the present invention, sensing of a plurality of types of gases existing in an atmosphere is achieved with low cost.　This gas sensor chip comprises a semiconductor substrate, and a plurality of gas detection material layers that are each formed at different positions on the semiconductor substrate. Each of the gas detection material layers has a metal oxide layer, and a catalytic metal layer formed above the metal oxide layer, and is configured so that the catalytic metal layer is exposed to the atmosphere. The plurality of gas detection material layers have mutually differing combinations of type, film thickness, and crystal grain size of the material of the metal oxide layer and type, film thickness, and crystal grain size of the material of the catalytic metal layer.

Description

Gas sensor chip, gas sensing system, and method for manufacturing the gas sensor chip

The present invention relates to a gas sensor chip, a gas sensing system, and a method for manufacturing a gas sensor chip.

In order to realize a decarbonized society, technologies that use hydrogen and carbon-neutral biofuels instead of fossil fuels to generate electricity are attracting attention. As people around the world become more environmentally conscious, there is also growing interest in pollutant components in the air. Interest in well-being is also growing, and people are beginning to want to monitor their health status, for example by breath sensing, and live in comfortable environments. As a result, in addition to the growing need to sense a single type of gas, such as hydrogen, there is also a growing need to independently detect the concentration of each gas component in an atmosphere containing multiple types of gases, and to separate and distinguish combination patterns of multiple types of gas components.

On the other hand, Patent Document 1 describes a gas sensor technology consisting of a gas molecule detection section and an array of amplifier circuits.

Non-Patent Document 1 also describes a hydrogen sensor, which is one type of gas sensor. There are several types of hydrogen sensors that have different detection principles. Among these, sensors such as FET type, capacitor type, and diode type are classified as work function type sensors.

International Publication No. 2017/104130

In order to detect the types of gases present in the atmosphere or the component patterns of each gas, multiple types of gas sensor elements with different characteristics for different types of gas or gas concentrations are required. Generally, producing such multiple types of gas sensor elements individually or obtaining them individually results in high costs.

However, neither Patent Document 1 nor Non-Patent Document 1 describes a technique for producing the above-mentioned multiple types of gas sensor elements at low cost, making it difficult to realize low-cost sensing of multiple types of gases present in the atmosphere.

Due to the above circumstances, there is a demand for technology that can realize low-cost sensing of multiple types of gases present in the atmosphere.

As a means for solving the above problem, the technology described in the claims is used. As an example, a gas sensor chip may be used that includes a semiconductor substrate and a plurality of gas detection material layers each formed at a different position on the semiconductor substrate, the gas detection material layer having a metal oxide layer and a catalytic metal layer formed on the metal oxide layer, the catalytic metal layer being configured to be exposed to the atmosphere, and the plurality of gas detection material layers having different combinations of material type, film thickness, and crystal grain size of the metal oxide layer and material type, film thickness, and crystal grain size of the catalytic metal layer.

As another example, a gas sensing system may be used that includes a gas sensor chip, a heater unit that heats the gas sensor chip, and a control unit that controls the gas sensor chip and the heater unit, the gas sensor chip includes a semiconductor substrate and a plurality of gas detection material layers each formed at a different position on the semiconductor substrate, the gas detection material layer includes a metal oxide layer and a catalyst metal layer formed on the metal oxide layer, and the catalyst metal layer is configured to be exposed to the atmosphere, the plurality of gas detection material layers have different combinations of material type, film thickness, and crystal grain size of the metal oxide layer and material type, film thickness, and crystal grain size of the catalyst metal layer, the control unit controls the heater unit so that the gas sensor chip is at a predetermined temperature, and detects gas in the atmosphere based on information obtained using the plurality of gas detection material layers.

As another example, a manufacturing method for a gas sensor chip may be used that includes the steps of forming an impurity layer on a semiconductor substrate, forming a first gas detection material layer including a catalytic metal layer on the semiconductor substrate, and forming a second gas detection material layer including a catalytic metal layer on a position on the semiconductor substrate different from that of the first gas detection material layer, wherein the first gas detection material layer and the second gas detection material layer are different from each other in at least one of the type of material constituting the gas detection material layer, the film thickness, and the crystal grain size.

The present invention makes it possible to realize low-cost sensing of multiple types of gases present in the atmosphere. Problems, configurations, and effects other than those described above will become clear from the description of the embodiments below.

1 is a diagram illustrating an example of a gas sensing system according to a first embodiment. 1 is a diagram illustrating an example of a hardware configuration of a gas sensing system according to a first embodiment. 1 is a plan view of a gas sensor chip according to a first embodiment; FIG. 2 is a diagram illustrating an example of a cross section of a sensor FET (SFET). FIG. 2 is a diagram illustrating an example of a cross section of a reference FET (RFET). FIG. 2 is a diagram showing an example of a material used for the gas sensing material layer of a sensor FET and a reference FET. 1A to 1C are diagrams showing an example of an operation for detecting the concentration of a detection target gas in a gas sensor chip using a FET type sensor. FIG. 1 is a diagram showing the characteristics of gate voltage versus drain current in an NFET-type sensor FET. FIG. 1 is a diagram showing gate voltage vs. drain current characteristics of an NFET-type reference FET. FIG. 13 is a diagram showing an example of the relationship between gas concentration and gate threshold voltage shift in a sensor FET. FIG. 2 shows an example of how two types of sensor FETs respond to a fixed concentration of several gases. 1 is a diagram for explaining that the concentrations of M types of gases can be estimated using N mutually different sensor FETs. FIG. 5 is a diagram showing an example of a comparison result of the size and cost of the gas sensor per type of gas between the gas sensor according to the first embodiment and a conventional gas sensor; FIG. FIG. 1 is a diagram showing a first example of an FET type gas sensor array using a selection transistor. FIG. 13 is a diagram showing a second example of an FET type gas sensor array using a selection transistor. FIG. 13 is a diagram showing a third example of an FET type gas sensor array using a selection transistor. FIG. 1 is a diagram showing an example of a FET-type gas sensor array using a TSV. FIG. 1 is a diagram showing an example of a FET type gas sensor array using an interposer. FIG. 1 is a diagram showing the characteristics of gate voltage versus drain current in a PFET-type sensor FET. FIG. 1 shows the gate voltage vs. drain current characteristics of a PFET-type reference FET. FIG. 1 is a diagram showing a first example of a device for determining a gas concentration by combining an NFET type sensor FET and a PFET type sensor FET. FIG. 13 is a diagram showing a second example of a device for determining a gas concentration by combining an NFET type sensor FET and a PFET type sensor FET. FIG. 2 is a diagram illustrating an example of a cross section of a sensor capacitor. FIG. 2 is a diagram illustrating an example of a cross section of a reference capacitor. 1A to 1C are diagrams showing an example of an operation for detecting the concentration of a detection target gas in a gas sensor chip using a capacitor-type sensor. FIG. 4 is a diagram showing an example of a characteristic curve of the capacitance of a sensor capacitor versus a gate voltage. FIG. 13 is a diagram showing an example of a characteristic curve of the capacitance of a reference capacitor versus a gate voltage. FIG. 2 is a diagram illustrating an example of a cross section of a sensor diode. FIG. 2 is a diagram illustrating an example of a cross section of a reference diode. 1A to 1C are diagrams showing an example of an operation for detecting the concentration of a detection target gas in a gas sensor chip using a diode-type sensor. FIG. 4 is a diagram showing an example of a current-to-voltage characteristic curve of a sensor diode. FIG. 2 is a diagram showing an example of a current vs. voltage characteristic curve of a reference diode. 5A to 5C are diagrams for explaining an example of a manufacturing method for the gas sensor chip according to the first embodiment. 5A to 5C are diagrams for explaining an example of a manufacturing method for the gas sensor chip according to the first embodiment. 5A to 5C are diagrams for explaining an example of a manufacturing method for the gas sensor chip according to the first embodiment. 5A to 5C are diagrams for explaining an example of a manufacturing method for the gas sensor chip according to the first embodiment. 5A to 5C are diagrams for explaining an example of a manufacturing method for the gas sensor chip according to the first embodiment. 5A to 5C are diagrams for explaining an example of a manufacturing method for the gas sensor chip according to the first embodiment. 5 is a flowchart showing an example of a method for manufacturing the gas sensor chip according to the first embodiment. 11A to 11C are diagrams for explaining a first modified example of the method for manufacturing the gas sensor chip. 11A to 11C are diagrams for explaining a first modified example of the method for manufacturing the gas sensor chip. 11A to 11C are diagrams for explaining a first modified example of the method for manufacturing the gas sensor chip. 11A to 11C are diagrams for explaining a first modified example of the method for manufacturing the gas sensor chip. 13 is a flowchart showing a first modified example of the method for manufacturing the gas sensor chip. 13A to 13C are diagrams for explaining a second modified example of the method for manufacturing the gas sensor chip. 13A to 13C are diagrams for explaining a second modified example of the method for manufacturing the gas sensor chip. 13A to 13C are diagrams for explaining a second modified example of the method for manufacturing the gas sensor chip. 13A to 13C are diagrams for explaining a second modified example of the method for manufacturing the gas sensor chip. 13A to 13C are diagrams for explaining a third modified example of the method for manufacturing the gas sensor chip. 13A to 13C are diagrams for explaining a third modified example of the method for manufacturing the gas sensor chip. 13A to 13C are diagrams for explaining a third modified example of the method for manufacturing the gas sensor chip. 13A to 13C are diagrams for explaining a third modified example of the method for manufacturing the gas sensor chip. 13A to 13C are diagrams for explaining a fourth modified example of the method for manufacturing the gas sensor chip. 13A to 13C are diagrams for explaining a fourth modified example of the method for manufacturing the gas sensor chip. 13A to 13C are diagrams for explaining a fourth modified example of the method for manufacturing the gas sensor chip. 13A to 13C are diagrams for explaining a fourth modified example of the method for manufacturing the gas sensor chip. 13A to 13C are diagrams for explaining a fourth modified example of the method for manufacturing the gas sensor chip. 13A to 13C are diagrams for explaining a fourth modified example of the method for manufacturing the gas sensor chip. FIG. 1 is a diagram showing an example of a gas sensing system in which a plurality of gas sensor chips are used at different temperatures.

Below, the embodiments are described in detail with reference to the drawings. In all the drawings used to explain the embodiments, components (parts) or functional blocks having the same function are given the same or related reference numerals, and repeated explanations are omitted. Furthermore, when there are multiple similar components (parts) or functional blocks, a symbol may be added to the generic reference numeral to indicate individual or specific components, etc. Furthermore, in the following embodiments, as a general rule, explanations of the same or similar parts will not be repeated unless specifically necessary.

In the drawings used in the embodiments, hatching may be omitted even in cross-sectional views to make the drawings easier to read. Hatching may also be added even in plan views to make the drawings easier to read.

In cross-sectional and plan views, the size of each part does not correspond to the actual device, and certain parts may be shown relatively large to make the drawings easier to understand. Even when cross-sectional and plan views correspond, certain parts may be shown relatively large to make the drawings easier to understand.

Configuration of the gas sensing system according to the first embodiment
1A is a diagram showing an example of a gas sensing system according to embodiment 1. As shown in FIG 1A, the gas sensing system 1000 includes a gas sensor chip 1001 and a circuit unit 1100.

The gas sensor chip 1001 has a FET type sensor, which is a type of work function sensor, i.e., a sensor FET array 1001SA including multiple sensor FETs (hereinafter also referred to as SFETs) 1001S, and one or more reference FETs (hereinafter also referred to as RFETs) 1001R. Furthermore, the gas sensor chip 1001 has a thermometer section 1001T and a heater section 1001H. The "reference FET" is an example of the "first FET" in the present invention.

The sensor FET1001S is one of the work function type sensors equipped with a catalytic metal gate, whose gate threshold voltage changes according to the concentration of various types of gases contained in the atmosphere (for details on the structure, effects, etc. of work function type sensors, see Non-Patent Document 1). The gate threshold voltage is the gate voltage at which a certain current flows between the drain and source of the FET when a certain voltage is applied between the drain and source. In this embodiment, a catalytic metal gate FET type gas sensor is used as the gas sensor element.

The reference FET 1001R is an FET element whose gate threshold voltage does not depend on the concentration of gas in the atmosphere. The reference FET 1001R is formed on the same gas sensor chip 1001 as the sensor FET array 1001SA. By comparing the gate threshold voltage of the sensor FET 1001S with the gate threshold voltage of the reference FET 1001R, more accurate gas sensing is possible, taking into account the fluctuation in FET characteristics due to temperature changes in the gas sensor chip 1001. Note that the reference FET 1001R may not be necessary if high accuracy is not required for gas sensing. Conversely, if high accuracy is required for gas sensing, multiple reference FETs 1001R may be formed on one gas sensor chip 1001, and the average or median value of the gate threshold voltages of the multiple reference FETs 1001R may be referenced.

The thermometer section 1001T is a device, element, or component capable of measuring the temperature of the gas sensor chip 1001. In this embodiment, the thermometer section 1001T includes a diode element, as an example. The diode element has a characteristic in which the relationship between the applied voltage and the current depends on the ambient temperature. By utilizing this characteristic, the ambient temperature can be determined by detecting the current of the diode element.

The heater section 1001H is a device, element, or member capable of heating and raising the temperature of the gas sensor chip 1001. In this embodiment, the heater section 1001H includes a heater wire (electric heating wire) as an example. The temperature of the gas sensor chip 1001 can be controlled by controlling the current flowing through the heater wire to adjust the amount of heat generated.

The circuit section 1100 is electrically connected to the gas sensor chip 1001. The circuit section 1100 has a gas concentration estimation section 1002, a control section 1003, a current detection section 1004, power sources 1005 to 1008, a parameter storage section 1009, and an I/O (Input/Output) section 1010.

The gas concentration estimation unit 1002 estimates the gas concentrations of multiple types of gases based on the information obtained from the gas sensor chip 1001.

The current detection unit 1004 detects the current of the various elements contained in the gas sensor chip 1001.

The power supplies 1005-1008 apply voltage to various elements or components (sites) on the gas sensor chip 1001 to supply power. It is assumed that the power supplies 1005-1008 will be used differently depending on the destination of the power supply, but they do not have to be used differently. The control unit 1003 is electrically connected to the power supplies 1005-1008, current detection unit 1004, gas concentration estimation unit 1002, parameter storage unit 1009, and I/O unit 1010, and controls and communicates with each of these units. The parameter storage unit 1009 stores various parameters necessary for the control or calculations performed by the control unit 1003. The I/O unit inputs and outputs information and power between the control unit 1003 and the outside of the gas sensing system 1000.

The heater section 1001H can heat the gas sensor chip 1001 and increase its temperature by applying a voltage from the power sources 1005-1008 to the heater wire that constitutes the heater section 1001H, causing a current to flow. The control section 1003 controls the power sources 1005-1008 so that a constant voltage is applied to the diode element that constitutes the thermometer section 1001T. The current detection section 1004 detects the current flowing through the diode element that constitutes the thermometer section 1001T under conditions where the voltage applied to the diode element is constant, and outputs the detected current value to the control section 1003. The parameter storage section 1009 stores parameters that define the relationship between the current flowing through the diode element and the temperature at that time. The control section 1003 refers to the parameters and determines the temperature of the gas sensor chip 1001 based on the detected current value. The control unit 1003 controls the power supplies 1005 to 1008 to adjust the voltage applied to the heater unit 1001H so that the temperature of the gas sensor chip 1001 is maintained at the target temperature.

The gas concentration estimation unit 1002 acquires physical quantities related to the voltage-current characteristics of the sensor FET array 1001SA and the reference FET 1001R according to the type or concentration of gas, and estimates the concentrations of various gases based on the acquired physical quantities. Details of the process of estimating the concentrations of various gases by the gas concentration estimation unit 1002 will be described later. Note that the "physical quantities" are an example of "information" in the present invention.

FIG. 1B is a diagram showing an example of the hardware configuration of the gas sensing system according to the first embodiment. In FIG. 1A, a control unit 1003, a gas concentration estimation unit 1002, a current detection unit 1004, and a parameter storage unit 1009 are represented as functional blocks. These functional blocks are configured in a semiconductor device 1020, for example, as shown in FIG. 1B. The semiconductor device 1020 includes a processor, such as a CPU (Central Processing Unit), an MPU (Micro Processor Unit), or an MCU (Micro Controller Unit), and a memory, and the processor executes a predetermined program stored in the memory, causing the semiconductor device 1020 to function as each of the above functional blocks.

FIG. 2 is a plan view of the gas sensor chip according to the first embodiment. As shown in FIG. 2, the gas sensor chip 1001 is formed with, for example, ten sensor FETs 1001S (with gates indicated as Gate 1 to 10) and one reference FET 1001R (with gate indicated as Gate 11). The sensor FET 1001S and the reference FET 1001R each have a gate, drain, source, and well, similar to well-known FETs. The sensor FET 1001S is a catalytic metal gate FET type gas sensor element.

The sensor FET1001S has a gas detection material consisting of a metal oxide layer and a catalytic metal layer mounted on the gate, and each sensor FET1001S differs from the others in either the material, film thickness, structure, or crystal grain size of the metal oxide layer, or the material, film thickness, structure, or crystal grain size of the catalytic metal layer. Different configurations of the gas detection material layer result in different selectivity and sensitivity to gas. Therefore, by using multiple sensor FET1001S each equipped with gas detection materials of different configurations and measuring their gate threshold voltages, it becomes possible to measure the component pattern of gas in an atmosphere containing multiple gas species.

The reference FET 1001R is a FET that does not react to the type or concentration of gas in the atmosphere. The reference FET 1001R is configured, for example, so that the gate that reacts to gas is not exposed to the atmosphere. The reference FET 1001R has a configuration that is basically the same as the sensor FET 1001S, except that the gate is not exposed to the atmosphere.

The gas sensor chip 1001 further includes a heater section 1001H and a thermometer section 1001T. The heater section 1001H is made of a heater wire, which is a wiring made of a metal such as aluminum, tungsten, or platinum. The heater wire can raise the temperature of the gas sensor chip 1001 above the ambient temperature by Joule heat generated by passing a current between both ends of the heater wire when power is supplied from the power sources 1005 to 1008. For example, the heater wire constituting the heater section 1001H can raise the temperature of the gas sensor chip 1001 by 100°C or more above the ambient temperature. In addition, the temperature of the gas sensor chip 1001 can be estimated by measuring the resistance between both ends of the heater wire. The thermometer section 1001T is made of a diode element. As described above, the temperature of the gas sensor chip 1001 can be estimated from the current value that flows when a constant voltage is applied to this diode element. By keeping the gas sensor chip 1001 at a predetermined temperature, the electrical characteristics of the sensor FET and reference FET can be stably maintained as expected.

The current detection unit 1004 shown in FIG. 1A measures the current flowing through the sensor FET 1001S, the reference FET 1001R, the heater wire constituting the heater unit 1001H, and the diode element constituting the thermometer unit 1001T, as described below. The parameter storage unit 1009 shown in FIG. 1A stores, for example, the voltage conditions to be applied to the sensor FET 1001S, the reference FET 1001R, the heater wire of the heater unit 1001H, and the diode element of the thermometer unit 1001T.

In FIG. 2, each electrode of each element is connected to a corresponding electrode pad. This configuration is an example to make the configuration of the gas sensor chip 1001 easier to understand. Therefore, for example, the wiring of multiple electrodes may be shared, and the number of electrode pads may be reduced to save space.

FIG. 3A is a schematic diagram showing an example of a cross section of a sensor FET (SFET). The main parts of the sensor FET 1001S are formed from a semiconductor substrate 1, a well 2, a source layer 3, a drain layer 4, a gate insulating film layer 5, a metal oxide layer 6 serving as a detection material, and a catalyst metal layer 7. The source layer and drain layer are also called the source diffusion layer and the drain diffusion layer.

The metal oxide layer 6 and the catalyst metal layer 7 are covered with an interlayer insulating film ILD, and an opening is formed in the interlayer insulating film ILD so that the surface of the catalyst metal layer 7 is exposed to an atmosphere containing the gas to be detected. The semiconductor substrate 1 may be made of, for example, silicon or silicon carbide (SiC). The metal oxide layer 6 may be made of, for example, titanium oxide, yttria-stabilized zirconia (YSZ), or the like. The catalyst metal layer 7 may be made of, for example, precious metals such as platinum, palladium, iridium, or nickel. As shown in FIG. 2, the gas sensor chip 1001 is equipped with a plurality of sensor FETs 1001S. The gas detection material layers of these sensor FETs 1001S are not all the same, and include layers with different configurations. The gas detection material layers in the plurality of sensor FETs 1001S include layers with different configurations, for example, at least one of the material type, film thickness, and crystal grain size of the metal oxide layer 6 and the material type, film thickness, and crystal grain size of the catalyst metal layer 7.

FIG. 3B is a schematic diagram showing an example of a cross section of a reference FET (RFET). The main parts of the reference FET 1001R are formed from a semiconductor substrate 1, a well 12, a source layer 13, a drain layer 14, a gate insulating film layer 15, a metal oxide layer 16 serving as a detection material, and a catalyst metal layer 17. The surface of the catalyst metal layer 17 is covered with an interlayer insulating film ILD, and is isolated from the atmosphere containing the gas to be detected. The metal oxide layer 16 and the catalyst metal layer 17 can be made of the same material as that used for any of the sensor FETs 1001S. Wiring layers made of metals such as aluminum, tungsten, and platinum are connected to the

wells

2 and 12, the source layers 3 and 13, the drain layers 4 and 14, the

catalyst metal layers

7 and 17, the diode element constituting the thermometer section 1001T, and the heater wire constituting the heater section 1001H, and can be powered from the power sources 1005 to 1008 shown in FIG. 1.

The sensor FET 1001S and the reference FET 1001R can both be N-type FETs or P-type FETs. The gas sensor chip 1001 includes multiple sensor FETs 1001S, and all of them can be N-type FETs or P-type FETs. Also, some of the sensor FETs 1001S can be formed from N-type FETs, and the remaining sensor FETs 1001S can be formed from P-type FETs. When only one reference FET 1001R is mounted on the gas sensor chip 1001, it can be formed from an N-type FET or a P-type FET. When multiple reference FETs 1001R are formed on the gas sensor chip 1001, the combination pattern of N-type FETs and P-type FETs is the same as that of the sensor FET 1001S.

FIG. 4 shows an example of materials used for the gas detection material layers of the sensor FET and the reference FET. FIG. 4 shows an example in which the gas detection material layers of the ten sensor FETs 1001S (with gates indicated as Gate1 to Gate10 in FIG. 2) have different types of materials for either the metal oxide layer 6 or the catalyst metal layer 7. In this way, the ten sensor FETs 1001S can have different sensitivities to the detection target gas. Although not shown in the figure, the metal oxide layers 6 can be formed to have different thicknesses or crystal grain sizes, or the catalyst metal layers 7 can be formed to have different thicknesses or crystal grain sizes, so that the sensitivities to the detection target gas can be made different from each other. The gas detection material layer of the reference FET 1001R (with gates indicated as Gate11 in FIG. 2) can be made the same as that of any of the sensor FETs 1001S, so that the gates can be formed at the same time, and therefore an increase in the number of steps involved in the manufacture of the gas sensor chip can be prevented.

FIG. 5 shows an example of the operation when detecting the concentration of a gas to be detected in a gas sensor chip using a FET type sensor. A current is passed through the heater wire constituting the heater section 1001H (Heater), and the gas sensor chip 1001 is heated to a predetermined temperature, for example, 100° C., by Joule heat generated by the resistance RHL of the heater wire. In this way, the temperature of the gas sensor chip is raised from the ambient temperature and kept constant, thereby making it possible to always stabilize the characteristics of the sensor. The power supplies 1005 to 1008 apply 0 V to the

wells

2 and 12 and

source layers

3 and 13 of the sensor FET 1001S and reference FET 1001R, and a drain voltage VD to the drain layers 4 and 14. The power supplies 1005 to 1008 also apply a variable voltage VGR to the gate of the reference FET 1001R, and a variable voltage VGS to the gate of the sensor FET 1001S. The current detection unit 1004 measures the current flowing through the drain terminals of the sensor FET 1001S and the reference FET 1001R. The control unit 1003 controls VGS and VGR so that both match a constant current Ic. The difference between VGR and VGS at this time is taken as VGRS and is defined as in Equation 1.

VGRS = VGR - VGS ... (Equation 1)

The difference between VGRS(0), which is the VGRS when the concentration of the gas to be detected in the atmosphere is 0, and VGRS(X), which is the VGRS when the concentration of the gas to be detected is X, is defined as ΔVg(X) in the following equation 2.

ΔVg(X) = VGRS(0) - VGRS(X) ... (Equation 2)

6A is a diagram showing the gate voltage vs. drain current characteristics of an NFET-type sensor FET. FIG. 6B is a diagram showing the gate voltage vs. drain current characteristics of an NFET-type reference FET. The gate voltage is also called the gate potential. In the NFET-type sensor FET 1001S, the catalyst metal layer 7, which is a gas detection material layer, is exposed, so the work function of the catalyst metal layer 7 changes depending on the detection target gas, and the gate voltage-drain current characteristics differ when the detection target gas concentration is 0 and when the detection target gas concentration is X. Specifically, as shown in FIG. 6A, when the detection target gas concentration increases, the characteristic curve showing the relationship between the gate voltage and the drain current moves in parallel in the voltage direction. As a result, the voltage VGS, which is the gate voltage when the current Ic, which is the threshold current, flows, changes from VGS(0), which is the VGS when the detection target gas concentration is 0, to VGS(X), which is the VGS when the detection target gas concentration is X. On the other hand, in the reference FET 1001R, the catalyst metal layer 17 is covered with the interlayer insulating film ILD, so the gate voltage-drain current characteristics do not change even if the gas concentration changes. Specifically, as shown in FIG. 6B, the current that flows when a voltage VGR is applied to the gate remains constant at Ic. As a result, ΔVg(X) in Equation 2 corresponds to the amount of change in the gate threshold voltage of the sensor FET 1001S with respect to the gas concentration X.

As shown in Equation 1, by using VGRS, which is the difference between the gate voltages of the sensor FET 1001S and the reference FET 1001R, the influence of noise caused by fluctuations in VGR and VGS due to temperature fluctuations, etc. can be suppressed by setting the drain current ID flowing through the drain terminal mentioned above to an appropriate value.

Note that if the effects of such noise can be sufficiently suppressed or ignored, for example, if gas concentration detection with relatively high accuracy is not required, the reference FET 1001R does not need to be used. In other words, the difference between VGS(0) when the target gas concentration in the detection atmosphere is 0 and VGS(X) when the target gas concentration is X is taken as ΔVg(X), and is defined as the following equation 3.

ΔVg(X) = VGS(0) - VGS(X) ... (Equation 3)

The ΔVg(X) defined in this way can be used as the gate threshold voltage shift (amount of change) of the sensor FET 1001S according to the gas concentration X of the gas to be detected. Note that while FIG. 5 shows an example in which the current is measured at the drain terminal, it is of course also possible to measure ΔVg by measuring the current at the source terminal side, as described later.

FIG. 7 is a diagram showing an example of the relationship between the gas concentration and the gate threshold voltage shift in the sensor FET. In FIG. 7, the value at which the gate threshold voltage shift ΔVg(X) is saturated in an environment where the gas concentration X is sufficiently high is set to ΔVgmax. FIG. 7 shows an example of the relationship between ΔVg and the gas concentration X when the FET-type gas sensor is held in an atmosphere of the gas concentration X for a sufficiently long time and reaches an equilibrium state. ΔVgmax may be a positive value or a negative value depending on the gas type. The gas concentration _X0 at which ΔVg(X) is 50% of ΔVgmax changes by changing the type of material, film thickness, and crystal grain size of the metal oxide layer 6, and the type of material, film thickness, or crystal grain size of the catalyst metal layer 7. The gate material dependency of the gas concentration _X0 changes by changing the type of gas to be detected. That is, the gate threshold voltage of the sensor FET changes depending on the type or concentration of the gas, and also changes when the type of material, film thickness, or crystal grain size of at least one of the metal oxide layer 6 and the catalyst metal layer 7 constituting the gate material changes.

FIG. 8A is a diagram showing an example of how two types of sensor FETs respond to a certain concentration of several gases. In FIG. 8A, hydrogen, hydrogen sulfide, ammonia, carbon monoxide, nitric oxide, and oxygen are used as examples of gas types. FIG. 8A also shows data for various gases plotted in a two-dimensional space consisting of ΔVg for two types of sensor FETs 1001S (here, examples are those with gates Gate1 and Gate5).

In general, data on various gases are plotted and differentiated in a space of dimensions according to the number of sensor FETs 1001S. That is, when N sensor FETs with different gas detection materials at the gates are mounted on the gas sensor chip 1001, data on various gases are plotted and differentiated in an N-dimensional space consisting of N ΔVg. For example, in the example shown in Figures 2 to 4, 10 sensor FETs 1001S with gates made of 10 different gas detection materials are mounted on the gas sensor chip 1001, so data on various gases are plotted and differentiated in a 10-dimensional space consisting of 10 ΔVg. Figure 8A illustrates the response to a single gas, but the measurement results for an atmosphere containing M types of gas species are plotted as different points in an N-dimensional space consisting of N ΔVg according to the concentration of each of the gas species contained, if M≦N. When N<M, the measurement results for atmospheres with different gas species and their respective concentrations will inevitably be plotted at the same point.

Based on the measurement results plotted in this way, it is possible to distinguish atmospheres of different gas types and gas concentrations as separate regions in an N-dimensional space, not only in the case of a single gas but also in the case of multiple gases. That is, by investigating in advance the pattern of the amount of change that affects each gate threshold voltage of N different sensor FETs for each gas type and concentration, it is possible to identify the gas types in the atmosphere and their concentrations by solving the simultaneous equations obtained from the above measurement results. Alternatively, by using artificial intelligence (AI) that has learned the correspondence between the pattern of the amount of shift in each gate threshold voltage of N different sensor FETs and the gas types in the atmosphere and their concentrations, it is possible to identify the gas types in the atmosphere and their concentrations from the above measurement results.

FIG. 8B is a diagram for explaining that the concentration of M types of gases can be estimated using N different sensor FETs. Consider the case where a plurality of sensor FETs 1001S equipped with N different gas detection material layers are used to measure the component pattern of an atmosphere containing M types of gases. If M≦N, as shown in FIG. 8B, the concentrations of M types of gases X_Gas1 to X_GasM can also be estimated based on the measured values ΔVg_Gate1 to ΔVg_GateN of the threshold voltage shifts of the N sensor FETs obtained from the N sensor FETs. Each of ΔVg_Gate1 to ΔVg_GateN is a function of the concentrations of M types of gases X_Gas1 to X_GasM. Strictly speaking, when M≦N, the number of equations (N: ΔVg_Gate1 to ΔVg_GateN) is greater than the number of variables (M: X_Gas1 to X_GasM), so there are cases where the values of the variables (X_Gas1 to X_GasM) cannot be determined. In this case, a method can be applied in which X_Gas1 to X_GasM are estimated so that the error between the actual measured values of ΔVg_Gate1 to ΔVg_GateN and the calculated values of the threshold voltage shifts ΔVg_Gate1_Calc to ΔVg_GateN_Calc obtained from the gas concentrations X_Gas1 to X_GasM is minimized. The error can be calculated, for example, by using the sum of the squares of the differences between the measured and calculated values of N threshold voltage shifts, that is, the following formula 4.

ΔVg_Sum=
(ΔVg_Gate1-ΔVg_Gate1_Calc) ² +
(ΔVg_Gate2-ΔVg_Gate2_Calc) ² +
(ΔVg_Gate3-ΔVg_Gate3_Calc) ² +
...
(ΔVg_GateN-ΔVg_GateN_Calc) ² ... (Equation 4)

X_Gas1 to X_GasM are estimated so that ΔVg_Sum shown in Equation 4 is minimized. The gas concentration estimation unit 1002 estimates the concentrations of various gases by performing processing based on the above-mentioned principles, based on the information obtained from the gas sensor chip 1001.

<Effects of the First Embodiment>
The gas sensor chip according to the first embodiment includes a semiconductor substrate and a plurality of gas detection material layers formed on the semiconductor substrate. The plurality of gas detection material layers each include a metal oxide layer and a catalytic metal layer formed on the metal oxide layer, and the catalytic metal layer is configured to be exposed to the atmosphere. In addition, in the gas sensor chip, the plurality of gas detection material layers are different from each other in combinations of the type of material, film thickness, and polycrystalline grain size of the metal oxide layer and the type of material, film thickness, and polycrystalline grain size of the catalytic metal layer. That is, the plurality of gas detection material layers are different from each other in at least one of the type of material constituting the gas detection material layer, the film thickness, and the polycrystalline grain size.

The gate threshold voltage of the gas sensor itself changes depending on the concentration of the gas to be detected. Therefore, each work function sensor included in the sensor array can be made to have different selectivity for multiple gas species contained in the atmosphere, making it possible to detect the concentrations of multiple types of gas with a single gas sensor chip and identify the type of odor based on the detected gas component pattern.

In the gas sensor chip according to the first embodiment, multiple types of work function sensors, each with different characteristics for the type or concentration of gas and each with a simple structure similar to a MOSFET, are formed on a single semiconductor substrate. As a result, a chip capable of sensing multiple types of gas can be manufactured at low cost. In other words, there is no need to incur high costs in preparing multiple types of gas sensors individually or to manufacture chips with costly structures. As a result, atmospheric gas sensing can be realized at low cost. Furthermore, because the work function sensor has a simple structure, stable operation can be expected and it is highly reliable.

FIG. 9 is a diagram showing an example of the results of comparing the size and cost of the gas sensor per type of gas between the gas sensor according to the first embodiment and a conventional gas sensor. By using the technology of the first embodiment, it is possible to integrate multiple sensor FETs having different gas detection materials on the same chip. Therefore, in the first embodiment, it is possible to reduce the size of the gas sensor per detectable gas type and reduce the cost per detectable gas type compared to the conventional technology.

The gas sensing system according to the first embodiment includes a gas sensor chip, a heater section for heating the gas sensor chip, and a control section for controlling the gas sensor chip and the heater section. The gas sensor chip includes a semiconductor substrate and a plurality of gas detection material layers formed at different positions on the semiconductor substrate. The gas detection material layer includes a metal oxide layer and a catalyst metal layer formed on the metal oxide layer, and is configured so that the catalyst metal layer is exposed to the atmosphere. The plurality of gas detection material layers are different from each other in combinations of the type of material, film thickness, and crystal grain size of the metal oxide layer, and the type of material, film thickness, and crystal grain size of the catalyst metal layer. The control section controls the heater section so that the gas sensor chip is at a predetermined temperature, and detects gas in the atmosphere based on information obtained using the plurality of gas detection material layers.

Such a gas sensing system can achieve the same effects as the gas sensor chip described above, and can, for example, achieve atmospheric gas sensing at low cost.

<Modification of the First Embodiment>
2 to 8 show examples in which electrode pads for supplying power to the source terminals, drain terminals, well terminals, and gate terminals of a plurality of sensor FETs and a reference FET are formed on a gas sensor chip. In addition to these examples, it is also possible to share terminals between sensor FETs, between reference FETs, or between a sensor FET and a reference FET. For example, it is possible to share a well terminal between P-type FETs (hereinafter also referred to as PFETs) and between N-type FETs (hereinafter also referred to as NFETs). It is also possible to share a source terminal when operating with a fixed source potential of 0V. In this way, by sharing the terminals or wiring connected to the terminals of the FETs mounted on the gas sensor chip, it is possible to reduce the number of electrode pads, reduce the chip area of the gas sensor, and reduce the cost per number of sensor FETs. The "electrode pad" connected to the source terminal or drain terminal and supplied with power from a power source is an example of the "power supply terminal" in the present invention.

In addition to the sensor FET and reference FET, the elements mounted on the gas sensor chip can include a selection transistor for selecting from these FETs the FET whose gate threshold voltage is to be measured. By using the selection transistor, it becomes possible to select and operate the terminals of multiple sensor FETs using a small number of electrode terminals. By controlling the on/off switching of the selection transistor, the selected sensor FET can be switched at high speed to collect information on the shift in the gate threshold voltage of each sensor FET, and the concentration of multiple gas species in the atmosphere can be measured.

FIG. 10 is a diagram showing a first example of a FET-type gas sensor array using a selection transistor. In the example shown in FIG. 10, all the sensor FETs 1001S are formed of NFETs, the sensor FETs 1001S share a well terminal and a source terminal, the gate terminal is independent for each sensor FET 1001S, and the drain terminal is shared via a selection FET 1001L. Here, a selection FET is used as the selection transistor. Note that the "selection FET" is an example of the "second FET" in the present invention.

The well terminal, source terminal, drain terminal, and gate terminal are connected to the circuit section 1100 in FIG. 1. To measure the gate threshold voltage of each sensor FET, it is necessary to measure the drain current or source current for each sensor FET. In the circuit shown in FIG. 10, if the drain terminal is shared without going through a selection FET, the sensor FET is placed in parallel between the drain terminal and the source current, making it impossible to distinguish which sensor FET the measured drain current (or source current) has flowed through. In other words, the gate threshold voltage cannot be measured. Therefore, a selection FET is placed so that only one of the multiple sensor FETs can be connected to the drain terminal.

In the circuit shown in FIG. 10, 24 selection FETs 1001L are used for eight sensor FETs 1001S. Each sensor FET 1001S is connected to the drain terminal via a selection FET series circuit in which three selection FETs are connected in series. As shown in FIG. 10, all three selection FETs connected to the top sensor FET 1001S are formed of NFETs, and all three selection FETs connected to the bottom sensor FET 1001S are formed of PFETs. For the sensor FETs 1001S in the other stages, the three selection FETs 1001L connected include both NFETs and PFETs. The gates of the eight selection FETs 1001L in the first row from the left are connected to each other, the gates of the eight selection FETs 1001L in the second row from the left are connected to each other, and the gates of the eight selection FETs 1001L in the third row from the left are also connected to each other.

A voltage corresponding to one of two values, High or Low, is applied to the gate of the selection FET 1001L in each column. An NFET is ON when the gate is High (H) and OFF when the gate is Low (L). Conversely, a PFET is OFF when the gate is High (H) and ON when the gate is Low (L). By arranging as shown in FIG. 10, only the uppermost sensor FET is connected to the drain terminal by setting all the gates of the selection FETs in the three columns to High (H). There are eight patterns of High and Low applied to the three gates of the selection FET series circuit: HHH, LHH, HLH, LLH, HHL, LHL, HLL, and LLL. Depending on each of these eight patterns, one of the eight sensor FETs is connected to the drain terminal.

As shown in FIG. 10, when the number of selection FETs connected in series is three, the drain terminals of eight (2 ^× 3) sensor FETs can be shared. By increasing the number of selection FETs connected in series, the number of sensor FETs that can share the drain terminal increases, and generally, by connecting N selection FETs in series, the drain terminals of 2 ^N sensor FETs can be shared. By using N selection FETs, the number of electrode pads increases by the number of gate terminals of the selection FETs, but the drain terminals of 2 ^N sensor FETs can be shared and reduced to one. Therefore, when a selection FET is used, the number of required electrode pads can be reduced by (2 ^N -1-N) compared to when a selection FET is not used. Therefore, when 3≦N, the number of electrode pads can be reduced by using a selection FET, and the effect of reducing the number of electrode pads becomes more pronounced as N increases.

In the example of FIG. 10, the sensor FET 1001S is configured as an NFET, but if the sensor FET 1001S is configured as a PFET, N series selection FETs can be used in the same way. In that case, the same effect can be obtained as when the sensor FET 1001S is configured as an NFET.

In the example of FIG. 10, the selection FET 1001L is formed using both an NFET and a PFET, but the present invention is not limited to this configuration.

FIG. 11 is a diagram showing a second example of a FET-type gas sensor array using selection transistors. As shown in FIG. 11, all the selection FETs can be formed of NFETs of the same conductivity type as the sensor FETs. In the example of FIG. 11, there are six shared gates in all the selection FETs, and two gates are paired. A high voltage is applied to one of the two gates in the same pair, and a low voltage is applied to the other. The voltage patterns applied to the six gates, in order from the left gate, are HLHLHL, LHHLHL, HLLHHL, LHLHHL, HLHLLH, LHHLLH, HLLHLH, and LHLHLH, and there are eight patterns of H/L patterns: HLHLHL, LHHLHL, HLLHHL, LHLHLH, and LHLHLH. Depending on the H/L pattern of the voltage applied to the six gates, one of the eight sensor FETs 1001S corresponding to the sensor FET 1001S is connected to the drain terminal.

As shown in FIG. 11, when the number of selection FETs connected in series is three, the drain terminals of eight (2 ^× 3) sensor FETs 1001S can be shared. Increasing the number of selection FETs connected in series increases the number of sensor FETs 1001S that can share the drain terminal. In general, by connecting N selection FETs in series, the drain terminals of 2 ^N sensor FETs 1001S can be shared. By connecting N selection FETs 1001L in series, the number of electrode pads increases by 2N gate terminals of the selection FETs 1001L. However, since the drain terminals of 2 ^N sensor FETs 1001S can be shared and reduced to one, the number of required electrode pads is reduced by (2 ^N -1-2N) compared to the case where the selection FET 1001L is not used. When 3≦N, the number of electrode pads can be reduced by using the selection FET 1001L, and the effect of reducing the number of electrode pads becomes more noticeable as N increases. The circuit configuration shown in Fig. 11 has a smaller effect of reducing the number of electrode pads, i.e., the effect of reducing the area of the gas sensor chip, than the circuit configuration shown in Fig. 10. However, in the case of the circuit configuration shown in Fig. 11, the circuit of the selection FET 1001L can be composed of only NFETs, which has the advantage of simplifying the circuit layout and reducing the number of steps in manufacturing the gas sensor chip.

In the example of FIG. 11, the sensor FET 1001S and the selection FET 1001L are configured as NFETs, but even if the sensor FET 1001S and the selection FET 1001L are configured as PFETs, N selection FETs can be connected in series and used in the same way. The effect is also the same as when the sensor FET 1001S and the selection FET 1001L are configured as NFETs.

FIG. 12 is a diagram showing a third example of a FET-type gas sensor array using a selection transistor. In the examples of FIG. 10 and FIG. 11, multiple sensor FETs 1001S are arranged in a one-dimensional direction, but as shown in FIG. 12, the sensor FETs 1001S can also be arranged two-dimensionally. In the example of FIG. 12, eight independent drain terminals, two shared gates for multiple selection FETs 1001L, and an array of 16 sensor FETs 1001S are shown. Both the sensor FETs 1001S and the selection FETs 1001L are composed of NFETs. Since there are eight independent drain terminals, eight sensor FETs 1001S can be selected simultaneously. By setting one of the two shared gates in the selection FET 1001L to High and the other to Low, eight sensor FETs 1001S can be selected and the gate threshold voltage can be measured.

In the example of FIG. 12, the sensor FET 1001S is an 8×2 array, but the number of independent drain terminals can be increased to more than 8, and the number of shared gates in the selection FET 1001L can be increased to more than 2. If the number of independent drain terminals is Nd and the number of shared gates in the selection FET is Ns, the number of sensor FETs 1001S is Nd×Ns. If the selection FET 1001L is not used, the number of drain terminals required is Nd×Ns, but by using Ns shared gates in the selection FET 1001L, the number of drain terminals can be reduced to Nd. Furthermore, by using the selection FET 1001L, the number of electrode pads can be reduced by Nd×Ns-Nd-Ns. For example, when Ns=2, the number of electrode pads can be reduced when 3≦Nd. Furthermore, when 3≦Ns, the number of electrode pads can be reduced when 2≦Nd.

In the configurations shown in the examples of Figures 10 and 11, when a current flows between the source terminal and the drain terminal, the current flows through N selection FETs 1001L connected in series, and when the drain current of the sensor FET 1001S is measured, the resistance of the N (3≦N) selection FETs 1001L connected in series affects the measurement of the drain current of the sensor FET 1001S as a parasitic resistance. On the other hand, in the configuration shown in the example of Figure 12, there is only one selection FET 1001L that acts as a parasitic resistance when measuring the drain current of the sensor FET 1001S, so the effect of the parasitic resistance of the selection FET 1001L can be suppressed more than in the configurations shown in the examples of Figures 10 and 11.

In the example of FIG. 12, the sensor FET 1001S and the selection FET 1001L are configured with NFETs, but an array of sensor FETs 1001S can also be formed when the sensor FET 1001S and the selection FET 1001L are configured with PFETs. The effect of this configuration is similar to that of the sensor FET 1001S and the selection FET 1001L configured with NFETs.

In the circuit examples described with reference to Figures 10 to 12, FETs are used as selection transistors, but other types of transistors, such as bipolar transistors, may also be used.

13 is a diagram showing an example of a FET-type gas sensor array using TSVs. In FIG. 13, the upper side shows a front view of the main part of a gas sensor chip 1001 on which the gas sensor array of this embodiment is formed, and the lower side shows a cross-sectional view of the gas sensor chip 1001. In the examples of FIGS. 10 to 12, an array of sensor FETs 1001S is formed using a selection FET 1001L, but as shown in FIG. 13, it is also possible to supply power to the source terminals, drain terminals, well terminals, and gate terminals of multiple sensor FETs 1001S using through electrodes (Through-Silicon Vias: TSVs) to the semiconductor substrate 1. With the configuration shown in FIG. 13, it is possible to arrange a large number of sensor FETs 1001S on the surface of the gas sensor chip 1001 on which the sensor FETs 1001S are formed without forming a selection FET and without being affected by wiring layout restrictions.

In the example of FIG. 13, a sensor FET 1001S made of an NFET and a sensor FET 1001S made of a PFET are formed in a gas sensor chip 1001. Furthermore, in the sensor FET 1001S made of an NFET, two types of thicknesses are used as the thickness of the silicon oxide film (SiO ₂ film) that becomes the gate insulating film. Similarly, in the sensor FET made of a PFET, two types of thicknesses are used as the thickness of the silicon oxide film (SiO ₂ film) that becomes the gate insulating film. In the example of FIG. 13, 10 nm and 20 nm are used as these two types of thicknesses. Of course, it is possible to use three or more types of thicknesses of the gate insulating film. The "silicon oxide film" is an example of the "impurity layer" in the present invention. In addition, "SiO ₂ " may be written as "SiO2" in order to improve visibility in the figure.

FIG. 14 is a diagram showing an example of a FET-type gas sensor array using an interposer. In FIG. 14, the upper side shows a front view of the main part of a gas sensor chip 1001 on which the gas sensor array of this embodiment is formed, and the lower side shows a cross-sectional view of the gas sensor chip 1001. As shown in FIG. 14, an interposer can also be used to supply power to the source terminals, drain terminals, well terminals, and gate terminals of multiple sensor FETs 1001S. As in the example of FIG. 13, it is possible to arrange a large number of sensor FETs 1001S without forming a selection FET on the surface of the gas sensor chip 1001 on which the sensor FETs 1001S are formed, and without being affected by wiring layout restrictions.

In the example of Fig. 14, similarly to the example of Fig. 13, a sensor FET 1001S made of an NFET and a sensor FET 1001S made of a PFET are formed on a gas sensor chip 1001. Furthermore, the sensor FET 1001S made of an NFET also uses two types of thickness for the silicon oxide film ( _SiO2 film) that serves as the gate insulating film. The sensor FET 1001S made of a PFET also uses two types of thickness for the silicon oxide film ( _SiO2 film) that serves as the gate insulating film. Of course, it is also possible to use three or more types of thickness for the gate insulating film.

Here, the characteristics of the gate voltage versus drain current in a PFET-type sensor FET will be explained. FIG. 15A is a diagram showing the characteristics of the gate voltage versus drain current in a PFET-type sensor FET. Also, FIG. 15B is a diagram showing the characteristics of the gate voltage versus drain current in a PFET-type reference FET. Note that the characteristics of the gate voltage versus drain current in an NFET-type sensor FET are as shown in FIG. 6.

In the PFET-type sensor FET 1001S, as in the NFET-type, the catalytic metal layer 7, which is a gas detection material layer, is exposed, so the work function of the catalytic metal layer 7 changes depending on the gas to be detected, and the gate voltage-drain current characteristics differ when the gas concentration to be detected is 0 and when the gas concentration to be detected is X. Specifically, as shown in FIG. 15A, when the gas concentration to be detected increases, the characteristic curve representing the relationship between the gate voltage and the drain current moves parallel to the voltage direction. As a result, the voltage VGS, which is the gate voltage when the current Ic, which is the threshold current, flows, changes from VGS(0), which is the VGS when the gas concentration to be detected is 0, to VGS(X), which is the VGS when the gas concentration to be detected is X. On the other hand, in the reference FET 1001R, the catalytic metal layer 17 is covered with the interlayer insulating film ILD, so the gate voltage-drain current characteristics do not change even if the gas concentration changes. Specifically, as shown in FIG. 15B, the current flowing when the voltage VGR is applied to the gate remains constant at Ic. As a result, ΔVg(X) in Equation 2 corresponds to the gate threshold voltage shift (amount of change) of the sensor FET 1001S relative to the gas concentration X.

Even if the sensor FET is changed from an NFET to a PFET, the characteristic curve of drain current versus gate voltage still shifts parallel to the voltage direction, but when the current is measured while keeping the gate voltage constant, the increase or decrease in drain current in response to the same gas is opposite for NFET and PFET. For NFET, when the gate threshold voltage shifts to the negative side, the absolute value of the drain current at a constant gate voltage increases, and when the gate threshold voltage shifts to the positive side, the absolute value of the drain current at a constant gate voltage decreases. On the other hand, for PFET, when the gate threshold voltage shifts to the negative side, the absolute value of the drain current at a constant gate voltage decreases, and when the gate threshold voltage shifts to the positive side, the absolute value of the drain current at a constant gate voltage increases.

By utilizing this property and combining an NFET type sensor FET and a PFET type sensor FET, it is possible to configure a device that determines whether the gas concentration in the atmosphere for a certain gas species is within a certain concentration range, for example, 1 ppm to 10 ppm. Here, we consider as an example the case of a gas species whose gate threshold voltage shifts toward the negative voltage direction depending on the gas concentration.

FIG. 16 is a diagram showing a first example of a device that determines a gas concentration by combining an NFET-type sensor FET and a PFET-type sensor FET. For example, as shown in FIG. 16, in a device in which an NFET-type sensor FET and a PFET-type sensor FET are connected in series, 1 V and 0 V are applied to the terminals at both ends of the device. In the PFET, 1 V is applied to the well so that no forward bias is applied between the source-drain layer and the well, and 0 V is applied to the well of the NFET. A voltage VG_NFET is applied to the gate of the NFET so that a current Ic, which is the determination current, flows when the gas concentration is 1 ppm. A voltage VG_PFET is applied to the gate of the PFET so that a current Ic, which is the determination current, flows when the gas concentration is 10 ppm.

In such a device, when the gas concentration is changed, if the gas concentration is lower than 1 ppm, the NFET current is smaller than Ic, so the PFET is ON but the device as a whole is OFF. If the gas concentration is between 1 ppm and 10 ppm, the current of both the NFET and PFET is larger than Ic, so the device as a whole is ON. Also, if the gas concentration is higher than 10 ppm, the PFET current is smaller than Ic, so the NFET is ON but the device as a whole is OFF. This operation of the NFET and PFET makes it possible to create a device that is ON overall only when the gas concentration is between 1 ppm and 10 ppm, and current flows between both ends.

FIG. 17 is a diagram showing a second example of a device that determines a gas concentration by combining an NFET-type sensor FET and a PFET-type sensor FET. For example, as shown in FIG. 17, in a device in which an NFET-type sensor FET and a PFET-type sensor FET are connected in parallel, 1 V and 0 V are applied to the terminals at both ends of the device. In the PFET, 1 V is applied to the well so that no forward bias is applied between the source-drain layer and the well, and 0 V is applied to the well of the NFET. In addition, a voltage VG_NFET is applied to the gate of the NFET so that a current Ic, which is the determination current, flows when the gas concentration is 10 ppm. A voltage VG_PFET is applied to the gate of the PFET so that a current Ic, which is the determination current, flows when the gas concentration is 1 ppm.

In such a device, when the gas concentration is changed, if the gas concentration is lower than 1 ppm, the PFET current becomes larger than Ic, so the NFET is in the OFF state but the device as a whole is in the ON state. If the gas concentration is between 1 ppm and 10 ppm, the current of both the NFET and the PFET becomes smaller than Ic and the device as a whole is in the OFF state. Also, if the gas concentration is higher than 10 ppm, the NFET current becomes larger than Ic, so the PFET is in the OFF state but the device as a whole is in the ON state. This operation of the NFET and PFET makes it possible to create a device that is in the OFF state overall only when the gas concentration is between 1 ppm and 10 ppm, and current flows between both ends when the gas concentration is outside this range.

In the examples of Figures 16 and 17, we have considered the case of a gas species in which the gate threshold voltage shifts toward a negative voltage depending on the gas concentration, but a similar device can also be constructed in the case of a gas species in which the gate threshold voltage shifts toward a positive voltage depending on the gas concentration.

<Another example of a work function type sensor: a capacitor type sensor>
1 to 17, a FET sensor, which is one of the work function sensors, is used, but a capacitor sensor, which is the same work function sensor, can be used instead of the FET sensor. That is, a sensor capacitor (SCAP) and a reference capacitor (RCAP) can be used instead of the sensor FET and the reference FET.

FIG. 18A is a schematic diagram showing an example of a cross section of a sensor capacitor. As shown in FIG. 18A, the sensor capacitor 1201S is formed from a semiconductor substrate 1, a well 2, a gate insulating film 5, a metal oxide layer 106 serving as a detection material, and a catalyst metal layer 107. The surface of the catalyst metal layer 107 of the sensor capacitor 1201S is exposed to an atmosphere containing the gas to be detected, and a part of the catalyst metal layer 107 is covered with an interlayer insulating film ILD for the purpose of fixing and protecting the catalyst metal layer 107. For example, silicon or silicon carbide (SiC) can be used for the semiconductor substrate 1.

FIG. 18B is a schematic diagram showing an example of a cross section of a reference capacitor. As shown in FIG. 18B, the reference capacitor 1201R is formed from a semiconductor substrate 1, a well 12, a gate insulating film layer 15, a metal oxide layer 116 serving as a detection material, and a catalyst metal layer 117. The surface of the catalyst metal layer 117 of the reference capacitor 1201R is covered with an interlayer insulating film ILD, and is isolated from the atmosphere containing the gas to be detected.

In addition, wiring layers made of metals such as aluminum, tungsten, and platinum are connected to the

wells

2 and 12 and the catalyst metal layers 107 and 117, and can be powered by the power sources 1005 to 1008 in Figure 1.

In the following, the sensor capacitor 1201S and the reference capacitor 1201R are described as both using N-

type wells

2 and 12, but P-type wells can also be used.

In a configuration in which a capacitor-type sensor is used in the gas sensor chip 1001, a source-drain layer is not required, compared to when a FET-type sensor is used, and this simplifies the structure of the gas sensor chip 1001. On the other hand, as described below, it becomes necessary to measure the capacitance using an AC voltage, which is not necessary when a FET-type sensor is used.

19 is a diagram showing an example of the operation when detecting the concentration of a target gas in a gas sensor chip using a capacitor-type sensor. A current is passed through the heater wire constituting the heater section 1001H, and the sensor capacitor 1201S and reference capacitor 1201R are heated to a predetermined temperature, for example, about 100°C, by Joule heat generated in the resistance RHL of the heater wire. 0V is applied to

wells

2 and 12 of the sensor capacitor 1201S and reference capacitor 1201R. A variable voltage VGR is applied to the gate of the reference capacitor 1201R by power supplies 1005 to 1008, and a variable voltage VGS is applied to the gate of the sensor capacitor 1201S by power supplies 1005 to 1008. In addition to the DC voltages VGR and VGS, an AC voltage of amplitude Vsig is applied to the terminals of

wells

2 and 12 by power supplies 1005 to 1008. The capacitance C (SCAP) of the sensor capacitor 1201S and the capacitance C (RCAP) of the reference capacitor 1201R can be detected by measuring the AC current flowing through the gate terminals of the sensor capacitor 1201S and the reference capacitor 1201R using the current detection unit 1004. The control unit 1003 controls the variable voltages VGS and VGR so that both voltages match a constant capacitance C0. The difference VGRS between VGR and VGS at this time is the same as Equation 1.

FIG. 20A is a diagram showing an example of a characteristic curve of the capacitance vs. gate voltage of a sensor capacitor. FIG. 20B is a diagram showing an example of a characteristic curve of the capacitance vs. gate voltage of a reference capacitor. In the sensor capacitor 1201S, the catalyst metal layer 107 is exposed, so the work function of the catalyst metal layer 7 changes depending on the gas to be detected, and the characteristic curve of the capacitance vs. gate voltage moves parallel to the voltage direction when the concentration of the gas to be detected is 0 and when it is X. As a result, the gate voltage at which the capacitance becomes C0 changes from VGS(0) to VGS(X).

On the other hand, the reference capacitor 1201R has the catalytic metal layer 117 covered with the interlayer insulating film ILD, so that the capacitance vs. gate voltage characteristic does not change even if the concentration of the gas to be detected changes, and the capacitance value when the voltage VGR is applied to the gate remains constant at C0. As can be understood from the above explanation, the gas sensor chip 1001 using the sensor capacitor 1201S and the reference capacitor 1201R can detect the gas concentration based on the shift in the gate threshold voltage, similar to the case of using the sensor FET 1001S and the reference FET 1001R. In addition, by arranging multiple sensor capacitors 1201S on the gas sensor chip 1001 and applying different metal oxide layers 106 and catalytic metal layers 107 to the gas detection material layer that constitutes the gate, the sensitivity and selectivity to gas can be changed. As with the case of using the sensor FET, the component pattern of an atmosphere containing multiple gas species can be measured.

<Another example of a work function type sensor: a diode type sensor>
1 to 17, a FET sensor is used as the work function sensor, but a diode sensor may be used as the same work function sensor instead of the FET sensor. That is, a sensor diode (SDIODE) and a reference diode (RDIODE) may be used instead of the sensor FET and the reference FET.

FIG. 21A is a schematic diagram showing an example of a cross section of a sensor diode. As shown in FIG. 21A, the sensor diode 1301S is formed from a semiconductor substrate 1, a well 2, a metal oxide layer 106 serving as a detection material, and a catalyst metal layer 107. The surface of the catalyst metal layer 107 of the sensor diode 1301S is exposed to an atmosphere containing the gas to be detected, and a part of the catalyst metal layer 107 is covered with an interlayer dielectric film ILD for the purpose of fixing and protecting the catalyst metal layer 107. For example, silicon or silicon carbide (SiC) can be used for the semiconductor substrate 1.

FIG. 21B is a schematic diagram showing an example of a cross section of a reference diode. As shown in FIG. 21B, the reference diode 1301R is formed from a semiconductor substrate 1, a well 12, a metal oxide layer 116 serving as a sensing material, and a catalyst metal layer 117. The surface of the catalyst metal layer 117 of the reference diode 1301R is covered with an interlayer dielectric film ILD, and is isolated from the atmosphere containing the gas to be sensed.

wells

In the following, the sensor diode 1301S and the reference diode 1301R are described as both using N-type wells as

wells

2 and 12, but P-type wells can also be used.

The configuration using a diode-type sensor in the gas sensor chip 1001 has a simpler structure than when a FET-type sensor is used. In addition, there is no need for the AC voltage that is required when a capacitor-type sensor is used.

On the other hand, when a FET type sensor or a capacitor type sensor is used, no direct current flows through the

metal oxide layers

6, 16, 106, 116 or the

catalyst metal layers

7, 17, 107, 117 that serve as the gas detection material. However, when a diode type sensor is used, a direct current flows through the

metal oxide layers

106, 116 and the catalyst metal layers 107, 117.

FIG. 22 is a diagram showing an example of the operation when detecting the concentration of a gas to be detected in a gas sensor chip using a diode-type sensor. A current is passed through the heater wire constituting the heater section 1001H, and the sensor diode 1301S and the reference diode 1301R are heated to a predetermined temperature, for example, 100° C., by Joule heat generated in the resistance RHL of the heater wire. The power supplies 1005-1008 apply 0 V to the

wells

2 and 12 of the sensor diode 1301S and the reference diode 1301R. The power supplies 1005-1008 also apply a variable voltage VGR to the gate of the reference diode 1301R, and a variable voltage VGS to the gate of the sensor diode 1301S. The current detection section 1004 measures the current flowing through the gate terminals of the sensor diode 1301S and the reference diode 1301R. The control section 1003 controls VGS and VGR so that the currents of both diodes match a constant IC. The difference VGRS between VGR and VGS at this time is the same as Equation 1.

FIG. 23A is a diagram showing an example of a current-voltage characteristic curve of a sensor diode. FIG. 23B is a diagram showing an example of a current-voltage characteristic curve of a reference diode. Since the catalytic metal layer 107 is exposed in the sensor diode, the work function of the catalytic metal layer 7 changes depending on the gas to be detected, and the curve showing the current-gate voltage characteristic when the concentration of the gas to be detected is 0 and when it is X moves parallel to the voltage direction. As a result, the gate voltage at which the current becomes Ic changes from VGS(0) to VGS(X).

On the other hand, since the catalytic metal layer 117 of the reference diode is covered with the interlayer dielectric film ILD, the current-gate voltage characteristics do not change even if the concentration of the gas to be detected changes, and the capacitance value when a voltage VGR is applied to the gate remains constant at C0. As in the case of using a sensor FET and a reference FET, the gas concentration can be detected from the shift in the gate threshold voltage. In addition, by arranging multiple sensor diodes on a gas sensor chip and applying different metal oxide layers 106 and catalytic metal layers 107 to the gas detection material layer, the sensitivity and selectivity to gases can be changed. As in the case of using a sensor FET and a sensor capacitor, it is possible to measure the concentration of each gas in an atmosphere containing multiple gas species.

<Method of manufacturing gas sensor chip>
24A to 24F are diagrams for explaining an example of a method for manufacturing the gas sensor chip according to embodiment 1. Fig. 25 is a flowchart showing an example of a method for manufacturing the gas sensor chip according to embodiment 1. The method for manufacturing the gas sensor chip 1001 according to embodiment 1 is a method for fabricating a plurality of types of FETs having different gas detection material layers on a semiconductor substrate.

Here, multiple types of FETs refer to FETs used as sensor FETs and reference FETs. In other words, if the type of gas detection material layer of the reference FET overlaps with the type of gas detection material layer of any of the sensor FETs, the number of types of FETs fabricated will be the same as the number of types of sensor FETs. On the other hand, if the type of gas detection material layer of the reference FET does not overlap with the type of gas detection material layer of the sensor FET, the number of types of FETs fabricated will be the same as the number of types of sensor FETs + the number of types of reference FETs.

The flow of the manufacturing method of the gas sensor chip will be described. As shown in Fig. 25, in step S1, a well 2, a source layer 3, and a drain layer 4 are formed in a semiconductor substrate 1, and a gate insulating film 5 is formed thereon. The semiconductor substrate 1 is, for example, a silicon substrate. The gate insulating film 5 is, for example, an impurity layer and a _SiO2 film. In this step S1, the base of the FET is fabricated. Note that a conventionally known method can be used in this step S1.

In step S2, a resist is applied onto the semiconductor substrate 1 on which the base was prepared in step S1. The resist can be, for example, two layers, a lower layer resist and an upper layer resist, so that an undercut is formed when developed. In addition, for example, a lift-off process using a resist mask can be used to apply the resist in order to fabricate multiple sensor FETs with different gas detection material layers.

In step S3, an exposure process and a development process are used to form openings 40 on the semiconductor substrate 1 coated with resist in the areas (not necessarily in one place) where the catalytic metal layers of some of the sensor FETs will be formed.

In step S4, a metal oxide layer and a catalyst metal layer are formed on the semiconductor substrate 1 as a gas detection material layer. This step S4 is repeated for the number of types of FETs to be fabricated, as described below. When step S4 is performed the Nth time (N≧1), MOX(N) and CATAL(N) are used as the metal oxide layer and the catalyst metal layer. For example, when step S4 is performed the first time, a metal oxide layer MOX1 and a catalyst metal layer CATAL1 are formed (FIG. 24A). When step S4 is performed the second time, a metal oxide layer MOX2 and a catalyst metal layer CATAL2 are formed (FIG. 24C). For example, the first "metal oxide layer MOX1 and catalyst metal layer CATAL1" from the left in FIG. 24C is an example of the "first gas detection material layer" in the present invention. For example, the second from the left in FIG. 24C, "metal oxide layer MOX2 and catalyst metal layer CATAL2," is an example of the "second gas sensing material layer" in the present invention.

In step S5, the applied resist is removed. A metal oxide layer MOX1 and a catalyst metal layer CATAL1 are also formed on top of the upper resist by the process of step S4, but the metal oxide layer MOX1 and catalyst metal layer CATAL1 on top of the upper resist are also removed by removing the resist in step S5 (Figure 24B). As a result, a laminated film of the metal oxide layer MOX1 and catalyst metal layer CATAL1 is formed on the channel portion of some of the sensor FETs via the gate insulating film 5.

In step S6, a process is performed to determine whether all planned FETs have been produced. In other words, a process is performed to determine whether the number of types of FETs produced has reached the planned number. If it is determined in this step that all planned FETs have been produced, the process proceeds to step 7. On the other hand, if it is determined in this step that all planned FETs have not been produced, the process returns to step S2, and steps S2 to S5 are repeated until the number of types of FETs produced reaches the planned number.

For example, in the second execution of step S2, a resist is applied onto the semiconductor substrate 1, and an exposure process and a development process are performed. Then, in the second execution of step S3, an opening 40 is formed in an area where the catalyst metal layer of a part of the FET is to be formed, other than the area where the laminated film of the metal oxide layer MOX1 and the catalyst metal layer CATAL1 has already been formed (FIG. 24B). Next, in the second execution of step S4, a metal oxide layer MOX2 and a catalyst metal layer CATAL2 are formed (FIG. 24C). At this time, the metal oxide layer MOX2 is made to differ from MOX1 in any of the material, film thickness, and crystal grain size, or the catalyst metal layer CATAL2 is made to differ from CATAL1 in any of the material, film thickness, and crystal grain size. A metal oxide layer MOX2 and a catalyst metal layer CATAL2 are also formed on top of the upper resist layer, but by performing step S5 a second time, the resist is removed and the metal oxide layer MOX2 and catalyst metal layer CATAL2 on top of the upper resist layer are also removed.

By sequentially repeating steps S2 to S5 described above, it is possible to form multiple types of gas sensing material layers in which a catalyst metal layer is laminated on a metal oxide layer (Figure 24D). In the example of Figure 24D, eight types of gas sensing material layers Gate1 to Gate8 are formed, but of course the types of gas sensing material layers, i.e. the number of types of FETs, are not limited to this example. By changing the number of times steps 2 to 5 are repeated, it is possible to change the type of gas sensing material layer to be formed. In implementation, it is expected that, for example, several types to hundreds or thousands of types of gas sensing material layers will be formed.

After forming the required multiple types of gas detection material layers, a silicon oxide film and a silicon nitride film that will become the interlayer insulating film are formed in step S7 (Figure 24E). Note that in this step, although not shown, a process is performed by a known method to form contact holes in the interlayer insulating film made of the silicon oxide film and the silicon nitride film to supply power to the source, drain, well, and gate. In addition, a metal film such as aluminum or tungsten that will become the wiring is formed, and the wiring is formed by known lithography and dry etching techniques. Note that the "silicon nitride film" is an example of an "impurity layer" in the present invention.

Next, in step S8, an opening 50 is formed in the catalytic metal layer for the sensor FET in the interlayer insulating film, i.e., in the upper part of the gas detection material layer. This exposes the catalytic metal layer of the sensor FET to the atmosphere, completing the sensor chip (Figure 24F). Although not shown, when fabricating a reference FET, in step S8 shown in Figure 24F, when forming the opening 50 in the interlayer insulating film above the catalytic metal layer for the sensor FET, no opening is formed in the interlayer insulating film above the catalytic metal layer for the reference FET, and the interlayer insulating film is left.

In the gas sensor chip manufacturing method described with reference to Figures 24A to 24F, a method using a resist mask and a lift-off process when forming the gas detection material layer has been described as an example. However, the method is not limited to this, and it is of course possible to use other methods, such as a method using a metal mask. This also applies to the following modified examples.

The manufacturing method of the gas sensor chip according to the embodiment of the present invention includes the steps of forming an impurity layer on a semiconductor substrate, forming a first gas sensing material layer including a catalytic metal layer on the semiconductor substrate, and forming a second gas sensing material layer including a catalytic metal layer on a position on the semiconductor substrate different from that of the first gas sensing material layer. The first gas sensing material layer and the second gas sensing material layer are different from each other in at least one of the type of material constituting the gas sensing material layer, the film thickness, and the crystal grain size.

With this gas sensor chip manufacturing method, a gas sensor chip in which multiple types of work function type sensors are mounted on a single semiconductor substrate can be manufactured using a manufacturing method similar to that used for manufacturing a simple MOSFET, and the gas sensor chip can be manufactured at low cost. As a result, atmospheric gas sensing can be achieved at low cost.

In the gas sensor chip manufacturing method described above with reference to Figures 24A to 24F, a gas detection material layer consisting of a metal oxide layer and a catalytic metal layer is formed for each sensor FET in a continuous manner. However, as another method for manufacturing a gas sensor chip, a method is also conceivable in which a metal oxide layer or catalytic metal layer common to multiple sensor FETs is formed at once. That is, the process of forming multiple gas detection material layers, for example, the process of forming a first gas detection material layer and the process of forming a second gas detection material layer, may be divided into multiple film formation processes using a mask. The gas detection material layer includes, for example, one or more metal oxide layers and one or more catalytic metal layers, or includes one or more catalytic metal layers without including a metal oxide layer.

<Modification 1 of the manufacturing method of the gas sensor chip>
26A to 26D are diagrams for explaining the modified example 1 of the method for manufacturing the gas sensor chip, and Fig. 27 is a flow chart showing the modified example 1 of the method for manufacturing the gas sensor chip.

For example, as shown in FIG. 27, in step S11, similar to step S1 above, a well 2, a source layer 3, and a drain layer 4 are formed in a semiconductor substrate 1, and a gate insulating film 5 is formed thereon to create a base.

In step S12, a resist is applied to the semiconductor substrate 1 on which the base has been prepared.

In step S13, a process is performed in which openings are formed in the semiconductor substrate 1 coated with resist at positions corresponding to some combinations of FETs to be fabricated. When step S13 is performed for the second or subsequent times, the openings may be formed in positions corresponding to some combinations of all FETs to be fabricated, including FETs for which openings have previously been formed, or they may be positions corresponding to combinations of FETs for which openings have never previously been formed.

In step S14, a metal oxide layer MOX(N) is formed on the semiconductor substrate 1 with the openings formed therein. Here, N represents the number of times step S14 is performed; if it is performed the first time, a metal oxide layer MOX1 is formed, and if it is performed the second time, a metal oxide layer MOX2 is formed.

FIG. 26A shows an example in which openings are formed in the areas corresponding to the first to fourth FETs from the left on a semiconductor substrate 1 coated with resist, and a metal oxide layer MOX1 is formed on top of the openings.

In step S15, a process for removing the resist is performed. The metal oxide layer formed on the resist is removed together with the resist.

In step S16, it is determined whether or not another metal oxide layer is to be formed. If it is determined that another metal oxide layer is to be formed, the process returns to step S12. If it is determined that another metal oxide layer is not to be formed, the process proceeds to step S17. In other words, steps S12 to S15 are repeated until all of the metal oxide layers to be formed have been formed.

FIG. 26B shows an example of a state in which the resist is removed (step S15) and resist is applied (step S12) to the semiconductor substrate 1 shown in FIG. 26A, openings are formed in the areas corresponding to the first, second and fifth and sixth FETs from the left (step S13), and a metal oxide layer MOX2 is formed on top of the openings (step S15).

In other words, in the example of FIG. 26B, metal oxide layers MOX1 and MOX2 are laminated and formed in the portions of semiconductor substrate 1 corresponding to the first and second FETs from the left, metal oxide layer MOX1 is formed in the portions corresponding to the third and fourth FETs from the left, and metal oxide layer MOX2 is formed in the portions corresponding to the fifth and sixth FETs from the left.

FIG. 26C shows an example of a state in which the resist is removed (step S15) and resist is applied (step S12) to the semiconductor substrate 1 shown in FIG. 26B, openings are formed in the portions corresponding to the first, third, fifth, and seventh FETs from the left (step S13), and a metal oxide layer MOX3 is formed on top of the openings (step S15).

In other words, in the example of FIG. 26C, in the semiconductor substrate 1, metal oxide layers MOX1, MOX2, and MOX3 are formed in a laminated manner in the portion corresponding to the first FET from the left. Metal oxide layers MOX1 and MOX2 are formed in a laminated manner in the portion corresponding to the second FET from the left. Metal oxide layers MOX1 and MOX3 are formed in a laminated manner in the portion corresponding to the third FET from the left. Metal oxide layer MOX1 is formed in the portion corresponding to the fourth FET from the left. Metal oxide layers MOX2 and MOX3 are formed in a laminated manner in the portion corresponding to the fifth FET from the left. Metal oxide layer MOX2 is formed in the portion corresponding to the sixth FET from the left. Metal oxide layer MOX3 is formed in the portion corresponding to the seventh FET from the left. No metal oxide layer is formed in the portion corresponding to the eighth FET from the left.

In step S17, a resist is applied to the semiconductor substrate 1.

In step S18, a process is carried out to form openings in the semiconductor substrate 1 on which the resist has been applied, in areas corresponding to all of the FETs to be fabricated.

In step S19, a process is performed to form a catalyst metal layer CATAL1, which will become a gate, on the semiconductor substrate 1 with the opening formed therein. Note that, for example, the first gas sensing material layer from the left in FIG. 26D, i.e., the "metal oxide layers MOX1" to "MOX3" and the "catalyst metal layer CATAL1", are an example of the "first gas sensing material layer" in the present invention. Also, for example, the eighth gas sensing material layer from the left in FIG. 26D, i.e., the "catalyst metal layer CATAL1", is an example of the "second gas sensing material layer" in the present invention.

In step S20, a process of removing the resist is performed. The catalyst metal layer CATAL1 formed on the resist is removed together with the resist.
In step S21, a silicon oxide film and a silicon nitride film that will become an interlayer insulating film are formed.

In step S22, openings are formed in the semiconductor substrate 1 at positions corresponding to all FETs planned to be fabricated.

Note that, although not shown, when fabricating a reference FET, when forming an opening 50 in the interlayer insulating film at the gate portion of the FET, the interlayer insulating film above the catalyst metal layer of the reference FET is left without forming an opening. The process for fabricating this reference FET is also the same for the modified manufacturing method of the gas sensor chip shown below.

According to variant 1 of this gas sensor chip manufacturing method, as with the previous manufacturing method, a gas chip sensor having multiple types of sensor FETs formed therein can be manufactured.

For example, as shown in the example of FIG. 26B, for FETs that have the same structure before the deposition of the metal oxide layer MOX2, in terms of whether or not the metal oxide layer MOX1 is deposited, by depositing the metal oxide layer MOX2 on some FETs and not depositing the metal oxide layer MOX2 on the remaining FETs, it is possible to increase the variety of sensor FETs that have different gas detection material layers. This is because the structure of the gas detection material layer that was the same before the deposition of the metal oxide layer MOX2 becomes different after the deposition of the metal oxide layer MOX2.

Similarly, as shown in the example of FIG. 26C, for FETs that have the same stacked structure consisting of metal oxide layers MOX1 and MOX2 in the structure before the metal oxide layer MOX3 is deposited, the metal oxide layer MOX3 is deposited on some FETs and the metal oxide layer MOX3 is not deposited on the remaining FETs, thereby increasing the number of types of sensor FETs with different gas detection material layers.

Although not shown here, when fabricating a reference FET, when forming an opening 50 in the interlayer insulating film at the gate portion of the FET, the interlayer insulating film above the gate portion of the reference FET is left without forming an opening.

<Modification 2 of the manufacturing method of the gas sensor chip>
In the modified example 1 of the manufacturing method of the gas sensor chip, the catalytic metal layer is the same for all FETs (CATAL 1). However, it is also possible to form a catalytic metal layer of a plurality of different types. The modified example 2 of the manufacturing method of the gas sensor chip will be described below.

In the following explanations of each modified example, for simplicity, the processes of applying and removing the resist, forming an opening in the resist layer, and forming the interlayer insulating film will be omitted unless necessary. Similarly, the process of forming an opening in the interlayer insulating film above the gate portion of the sensor FET, and leaving an opening in the interlayer insulating film above the gate portion of the reference FET will be omitted unless necessary.

Figures 28A to 28D are diagrams for explaining modified example 2 of the manufacturing method of a gas sensor chip. For example, on a semiconductor substrate 1 on which a base is prepared by forming a well 2, a source layer 3, a drain layer 4, and a gate insulating film 5, a process is performed to form a metal oxide layer MOX1 for some combinations of FETs to be manufactured (Figure 28A). In addition, a process is performed to form a metal oxide layer MOX2 for some of the other combinations (Figure 28B). Next, a process is performed to form a catalyst metal layer CATAL1 that will become the gates of some of the FETs (Figure 28C), and a process is performed to form a catalyst metal layer CATAL2 that will become the gates of the remaining FETs (Figure 28D).

In the example shown in FIG. 28B, in FETs that are consistent in whether or not a metal oxide layer MOX1 is formed in the structure before the metal oxide layer MOX2 is formed, the metal oxide layer MOX2 is formed on some FETs, and the metal oxide layer MOX2 is not formed on the remaining FETs. This makes it possible to increase the variety of sensor FETs that have different gas detection material layers. This is because the structure of the gas detection material layer, which was the same before the metal oxide layer MOX2 was formed, becomes different by forming the metal oxide layer MOX2.

Also, in the sensor FETs shown in the examples of Figures 28C and 28D, in which the stacked structure consisting of the metal oxide layer MOX1 and the metal oxide layer MOX2 is the same in the structure before the formation of the catalyst metal layers CATAL1 and CATAL2, the catalyst metal layer CATAL1 is formed on one FET and the catalyst metal layer CATAL2 is formed on the remaining FET. This makes it possible to increase the types of sensor FETs with different gas detection material layers. This is because the structure of the gas detection material layer, which was the same before the formation of the catalyst metal layers CATAL1 and CATAL2, becomes different when the catalyst metal layers CATAL1 and CATAL2 are formed.

<Modification 3 of the manufacturing method of the gas sensor chip>
In the modified examples 1 and 2 of the manufacturing method of the gas sensor chip, a process of laminating metal oxide layers on one another is included, but the catalyst metal layer is made of a single layer of CATAL1 or a single layer of CATAL2, and a process of laminating catalyst metal layers on one another is not included. However, in addition to the process of laminating metal oxide layers on one another, a process of laminating catalyst metal layers on one another can be included to increase the types of gas detection materials of the sensor FET. The following describes modified example 3 of the manufacturing method of the gas sensor chip. In order to simplify the description, the process of applying and removing the resist and the process of forming the opening are omitted.

Figures 29A to 29D are diagrams for explaining modified example 3 of the manufacturing method of a gas sensor chip. For example, on a semiconductor substrate 1 on which a base has been created by forming a well 2, a source layer 3, a drain layer 4, and a gate insulating film 5, a process is performed to form a metal oxide layer MOX1 for some combinations of FETs to be manufactured (Figure 29A). A process is also performed to form a metal oxide layer MOX2 for some of the other combinations (Figure 29B). Next, a process is performed to form a catalyst metal layer CATAL1 that will become the gates of some of the FETs (Figure 29C). Next, a process is performed to form a catalyst metal layer CATAL2 that will become the gates of all FETs, including the FETs on which CATAL1 has been formed (Figure 29D).

In the FETs shown in Figure 29C, which have the same stacked structure consisting of metal oxide layers MOX1 and MOX2 in the structure before the catalyst metal layer CATAL1 is deposited, a process is performed to deposit the catalyst metal layer CATAL1 on one FET. Also, a process is performed to deposit the catalyst metal layer CATAL2 on the remaining FETs. By performing such a process, it is possible to increase the variety of sensor FETs with different gas detection material layers. This is because the structure of the gas detection material layer, which was the same before the catalyst metal layer CATAL1 was deposited, becomes different once the catalyst metal layer CATAL1 is deposited.

<Modification 4 of the manufacturing method of the gas sensor chip>
In the first to third variants of the gas sensor chip manufacturing method, the metal oxide layer is already a metal oxide film at the time of deposition, but it is also possible to deposit the metal layer as a metal layer at the time of deposition and then oxidize the metal layer in a subsequent process to form a metal oxide layer.

Figures 30A to 30F are diagrams for explaining modified example 4 of the manufacturing method of a gas sensor chip. For example, on a semiconductor substrate 1 on which a base is prepared by forming a well 2, a source layer 3, a drain layer 4, and a gate insulating film 5, a process is performed on some combinations of FETs to be manufactured, which will form a metal layer M1 that will become a metal oxide layer MOX1 in a later oxidation process (Figure 30A). A process is performed on some of the other combinations to form a metal layer M2 that will become a metal oxide layer MOX2 in a later oxidation process (Figure 30B). A process is performed on some of the still other combinations to form a metal layer M3 that will become a metal oxide layer MOX3 in a later oxidation process (Figure 30C). Then, a process is performed to form a catalyst metal layer CATAL1 that will become the gate of all the FETs (Figure 30D).

The semiconductor substrate 1 in the form shown in FIG. 30D is subjected to a process for removing the resist (FIG. 30E). After that, by annealing in air at a temperature of about 400° C., the metal layers M1, M2, and M3 become metal oxide layers MOX1, MOX2, and MOX3, respectively (FIG. 30F). When the metal layers M1, M2, and M3 are oxidized, volume expansion occurs. By appropriately selecting the type and thickness of the metal layers M1, M2, and M3 and the catalyst metal layer CATAL1, the expanded MOX1, MOX2, and MOX3 can penetrate into the grain boundaries of the top catalyst metal layer CATAL1, forming a nanostructure of the catalyst metal layer CATAL1. The nanostructure of the catalyst metal layer CATAL1 is an effective structure for improving the sensitivity of gas sensors.

As shown in FIG. 30B, in FETs in which the state of whether or not the metal layer M1 is formed on the semiconductor substrate 1 before the metal layer M2 is formed is the same, by forming the metal layer M2 on some FETs and not forming the metal layer M2 on the remaining FETs, it is possible to increase the types of sensor FETs with different gas detection material layers. This is because the structure of the gas detection material layer, which was the same before the metal layer M2 was formed, becomes different when the metal layer M2 is formed. Similarly, as shown in FIG. 30C, in FETs in which the stacked structure consisting of the metal layer M1 and the metal layer M2 on the semiconductor substrate 1 before the metal layer M3 is formed is the same, by forming the metal layer M3 on some FETs and not forming the metal layer M3 on the remaining FETs, it is possible to increase the types of sensor FETs with different gas detection material layers.

<Fifth modified example of the manufacturing method of the gas sensor chip>
As a special example, consider the case of forming a film of a mixed crystal material such as YSZ (yttria stabilized zirconia). The composition formula of YSZ can be written as (ZrO ₂ ) _1-Z (Y ₂ O ₃ ) _Z. For example, the film formation of ZrO ₂ and the film formation of Y ₂ O ₃ are alternately performed in N film formations, and the film thickness (number of moles per unit area) of the film formed in these N film formations is also all different. With this method, ^2N sensor FETs can be made with different YSZ compositions Z, i.e., different gas detection materials. Since the sensitivity and selectivity of the sensor change depending on the difference in the gas detection material, it becomes possible to detect multiple gases.

In addition, _CeO2 and _Gd2O3 can also be mixed crystals, and the composition formula can be written as ( _CeO2 ) _1-Z ( _Gd2O3 ) _Z . For example, _CeO2 _{and Gd2O3} _are alternately formed in N film formations, and the film thicknesses (number of moles per _unit area) of the films formed in these ^{N film formations are all different. With this method, 2N} _sensor FETs can be made with different compositions Z of ( _CeO2 ) _1-Z ( _Gd2O3 ) _Z , _i.e. , different gas detection materials. The sensitivity and selectivity of the sensor change depending on the gas detection material, making it possible to detect multiple gases.

Also, BaCe _1-Z Y _Z O ₃ , BaZr _1-Z Y _Z O ₃ , SrCe _1-Z Y _Z O ₃ , SrZr _1-Z Y _Z O ₃ , etc. are mixed crystals. In the case of _{BaCe 1-Z} Y _Z O ₃ , for example, BaCeO ₃ and BaYO _3-δ are alternately formed in N film formations, and the film thickness (moles per unit area) of the film formed in these N film formations is also changed. ^{2 N} sensor FETs can be made so that the composition Z of BaCe _1-Z Y _Z O ₃ , that is, the gas detection material, is different from each other. Since the sensitivity and selectivity of the sensor change depending on the gas detection material, it is possible to detect multiple gases. The same is true for BaZr _1-Z Y _Z O ₃ , SrCe _1-Z Y _Z O ₃ and SrZr _1-Z Y _Z O ₃ .

<Modification 6 of the manufacturing method of the gas sensor chip>
In the gas sensor chip manufacturing method and its modified examples described so far, the metal oxide layer or the metal layer to be the metal oxide layer and the catalytic metal layer are formed separately. However, the metal oxide layer can also function as the gate of an FET by doping it with catalytic metals such as platinum, palladium, iridium, rhodium, and ruthenium. These catalytic metals can function as the catalytic metal layer if the resistance of the metal oxide layer can be reduced to a level where it can function as a gate by imparting electrical conductivity to the metal oxide layer. In other words, the catalytic metal layer can include a metal oxide layer.

In the fourth variation of the manufacturing method of the gas sensor chip described above, the metal layers M1, M2, and M3, which will become metal oxides in subsequent processes, can also be doped with catalytic metals such as platinum, palladium, iridium, rhodium, and ruthenium. In the oxidation process shown in the example of FIG. 30F, the metal layers M1, M2, and M3 become metal oxide layers MOX1, MOX2, and MOX3, each of which contains a doped catalytic metal. These catalytic metals can function as catalytic metal layers if the resistance of the metal oxide layer can be reduced to a level where it can function as a gate by making the metal oxide layer electrically conductive. In other words, the catalytic metal layer can contain a metal oxide layer.

<Effects of the Modified Method of Manufacturing the Gas Sensor Chip>
In the above-mentioned first to sixth variations of the manufacturing method of the gas sensor chip, the types of gas sensing material layers can be increased by up to two times each time a material layer is deposited. Reflecting the fact that a catalyst metal layer is required for every sensor FET, ^2N types of gas sensing material layers can be formed by N+1 material depositions. Therefore, when a large number of types of sensor FETs are required on the gas sensor chip, the first to sixth variations of the manufacturing method of the gas sensor chip can exponentially reduce the number of manufacturing steps of the gas sensor chip. For example, in the manufacturing method of the gas sensor chip described with reference to Figs. 24A to 24F, 1024 lithography steps are required to separately produce 1024 types of gas sensing materials, whereas the first to sixth variations of the manufacturing method of the gas sensor chip require only 11 lithography steps.

<Sensing system using the gas sensor according to the first embodiment>
8B, when the number N of types of detection materials of the sensor FET mounted on the gas sensor chip is compared with the number M of types of gas components contained in the atmosphere, and M≦N, for example, by minimizing ΔVg_Sum in (Equation 4), X_Gas1 to X_GasM can be estimated. On the other hand, when N<M, X_Gas1 to X_GasM cannot be estimated.

However, by changing the temperature of the gas sensor chip, the sensitivity and selectivity of the sensor FET to the gas to be detected can be changed, so that the same sensor FET can be considered as a new sensor FET with different properties by changing the temperature. Even if N sensors on the same gas sensor chip are used, if measurements are performed at two temperatures T1 and T2, information equivalent to that obtained by measuring with 2N different sensor FETs can be obtained. Therefore, even if N<M, if M≦2N, X_Gas1 to X_GasM can be estimated by minimizing ΔVg_Sum(T1, T2), defined by the following equation 5, for the shift in 2N gate threshold voltages.

ΔVg_Sum(T1, T2)=
{ΔVg_Gate1(T1)-ΔVg_Gate1_Calc(T1)} ² +
{ΔVg_Gate2(T1)-ΔVg_Gate2_Calc(T1)} ² +
...
{ΔVg_GateN(T1)-ΔVg_GateN_Calc(T1)} ² +
{ΔVg_Gate1(T2)-ΔVg_Gate1_Calc(T2)} ² +
{ΔVg_Gate2(T2)-ΔVg_Gate2_Calc(T2)} ² +
...
{ΔVg_GateN(T2)-ΔVg_GateN_Calc(T2)} ²
... (Equation 5)

Equation 5 is an example of measurements at two different temperatures, but this equation can be generalized. When P gas sensor chips, each equipped with N sensor FETs with different gas detection material layers, are prepared and each gas sensor chip is used at different temperatures T1 to TP to measure the gas components in the atmosphere, X_Gas1 to X_GasM can be estimated if M≦N×P.

FIG. 31 is a diagram showing an example of a gas sensing system in which multiple gas sensor chips are used at different temperatures. The gas sensing system 2000 shown in FIG. 31 includes multiple gas sensor chips 2001 and a system control unit 2003 that controls them. The gas sensor chip 2001 is equipped with multiple sensor FETs with different gas detection material layers. Each gas sensor chip 2001 is equipped with a heater unit (Heater), such as a heater wire, that can independently heat the gas sensor chip 2001. That is, the gas sensing system 2000 includes multiple gas sensor chips 2001 and multiple heater units. The gas sensor chip 2001 also includes a thermometer unit (Thermometer), such as a diode, that can measure temperature. The system control unit 2003 is a systemized version of the circuit unit 1100 in FIG. 1 that can control multiple gas sensors. The system control unit 2003, like the control unit 1003 in FIG. 1, includes a gas concentration estimation unit 2002, a current detection unit 2004, a power source 2005, and a parameter storage unit 2009.

<Effects of a gas sensing system using multiple gas sensor chips at different temperatures>
31, it is possible to measure the gas components in the atmosphere at multiple temperatures, three temperatures T1 to T3° C. in the example of FIG. 31, so that X_Gas1 to X_GasM can be estimated if M≦N×NC, where NC is the number of gas sensor chips. The temperatures T1, T2, and T3 can be, for example, 100° C., 200° C., and 300° C.

<Modifications of the present invention>
The present invention is not limited to the above-described embodiment, and includes various modified examples. For example, the above-described embodiment has been described in detail to clearly explain the present invention, and is not necessarily limited to those having all of the configurations described. In addition, it is possible to replace a part of the configuration of one embodiment with the configuration of another embodiment, and it is also possible to add the configuration of another embodiment to the configuration of one embodiment. In addition, it is possible to add, delete, or replace a part of the configuration of each embodiment with another configuration.

<Additional Notes>
This application discloses an inexpensive gas sensor chip in which a plurality of gas sensor elements with different sensitivities and selectivities are integrated on a semiconductor substrate, and the amount of each of a plurality of gas species contained in an atmosphere can be measured. For example, a gas detection material layer having at least one of different material types, film thicknesses, and crystal grain sizes is formed on an impurity layer on a semiconductor substrate, thereby forming a plurality (N) of work function type sensors (e.g., sensor FETs) with different gas sensitivities and selectivities. Based on the measurement results of the change in the electrical characteristics of the N sensors in an atmosphere, the amount of each gas component of 1 to M (M≦N) types of gas species can be measured, and it becomes possible to distinguish between atmospheres with different gas species and concentrations of each gas species, for example.

An example of a gas sensor according to an embodiment of the present application is formed on a semiconductor substrate, and a gas detection material layer is mounted on the gate, the gas detection material layer being composed of at least one metal oxide layer having different material types, film thicknesses, or polycrystalline grain sizes, and at least one catalytic metal layer having different material types, film thicknesses, or polycrystalline grain sizes. The metal oxide layer and the catalytic metal layer have a plurality of catalytic metal gate FET type sensor elements in which the catalytic metal layer is formed on the upper layer of the metal oxide layer and exposed to the atmosphere. The catalytic metal gate FET type sensors can be formed as either N-type or P-type, or may be formed using both N-type and P-type. A catalytic metal gate FET type sensor circuit can be formed by combining a plurality of catalytic metal gate FET type sensors in the array. A selection transistor for accessing a specific sensor from an array consisting of a plurality of catalytic metal gate FET type sensors can be formed separately from the catalytic metal gate FET type sensor using a normal gate material that does not react with gas. Furthermore, the catalytic metal layer and metal oxide layer of the gate layer may be the same as any of the plurality of catalytic metal gate FET type sensors, and one or more reference FETs may be mounted, the gate of which is covered with a protective film and not exposed to the atmosphere. A heater wire for heating and controlling the temperature of the catalytic metal gate FET sensor element, and a diode element that serves as a thermometer for estimating the temperature of the catalytic metal gate FET sensor element can also be mounted on the semiconductor substrate. Power can be supplied to the catalytic metal gate FET sensor element, the reference FET, the heater wire, the diode, etc. from an external power source via wire bonds, or TSV technology can be used to supply power by forming a hole penetrating the substrate.

An example of an embodiment of the present invention is described below.
[Appendix 1]
A semiconductor substrate;
a plurality of gas-sensing material layers each formed at a different location on the semiconductor substrate;
Equipped with
the gas sensing material layer has a metal oxide layer and a catalytic metal layer formed on the metal oxide layer, the catalytic metal layer being exposed to the atmosphere;
the plurality of gas detection material layers are different from one another in combination of the type of material, thickness, and crystal grain size of the metal oxide layer, and the type of material, thickness, and crystal grain size of the catalytic metal layer;
Gas sensor chip.

[Appendix 2]
In the gas sensor chip according to [Appendix 1],
a gate insulating film layer and a well are provided between the metal oxide layer and the semiconductor substrate, and the gas detection material layer is used as a gate layer for each of the gas detection material layers, thereby forming a plurality of sensor capacitors.
Gas sensor chip.

[Appendix 3]
In the gas sensor chip according to [Appendix 1],
a plurality of sensor diodes are formed by using each of the plurality of gas detection material layers as a gate layer and providing a well between the metal oxide layer and the semiconductor substrate, for each of the plurality of gas detection material layers;
Gas sensor chip.

[Appendix 4]
In the gas sensor chip according to [Appendix 1],
a heater wire capable of raising the temperature of the gas sensor chip from an environmental temperature by supplying electric power via an electrode terminal;
Gas sensor chip.

[Appendix 5]
In the gas sensor chip according to [Appendix 1],
a diode capable of measuring a temperature of the gas sensor chip by measuring a current through an electrode terminal;
Gas sensor chip.

1: Semiconductor substrate 2, 12: Well 3, 13: Source layer 4, 14: Drain layer 5, 15: Gate insulating

film layer

6, 16, 106:

Metal oxide layer

7, 17, 107: Catalyst metal layer 40: Opening in resist 50: Opening in interlayer insulating film 1000, 2000: Gas sensing system 1001, 2001: Gas sensor chip 1001H: Heater section (Heater)
1001R...Reference FET (RFET)
1001S...Sensor FET (SFET)
1001SA: Sensor FET array 1001T: Thermometer
1002, 2002... Gas concentration estimation unit 1003... Control unit 2003...

System control unit

1004, 2004...

Current detection unit

1005, 1006, 1007, 1008, 2005...

Power supply

1009, 2009... Parameter storage unit 1010... I/O unit 1020... Semiconductor device 1201S... Sensor capacitor (SCAP)
1201R...Reference capacitor (RCAP)
1301S...Sensor diode (SDIODE)
1301R...Reference diode (RDIODE)
ILD: Interlayer insulating film X, _X0 : Gas concentration X_Gas1, X_GasM: Gas concentration RHL: Heater wire resistance VD: Drain voltage VSS: Source, well voltage Ic, Ic(X): Current VGS, VGS(X), VGS(0), VGS(X,Y): Voltage VGR, VGRS: Voltage A: Ammeter ID(SFET): Drain current of sensor FET ID(RFET): Drain current of reference FET IS(SFET): Source current of sensor FET C0: Capacitance C(SCAP): Capacitance of sensor capacitor C(RCAP): Capacitance of reference capacitor I(SDIODE) .. Current of sensor diode I (RDIODE)... Current of reference diode ΔVg, ΔVg(X)... Threshold voltage shift of gas sensor ΔVgmax... Maximum value of threshold voltage shift of gas sensor ΔVg_Gate1, ΔVg_Gate5, ΔVg_GateN: Measured value of threshold voltage shift of gas sensor ΔVg_Gate1_Calc, ΔVg_GateN_Calc: Calculated value of threshold voltage shift of gas sensor Vsig... Amplitude of AC voltage MOX1, MOX2, MOX3... Metal oxide layers CATAL1, CATAL2... Catalyst metal layers M1, M2, M3... Metal layer Z... Composition

Claims

A semiconductor substrate;
a plurality of gas-sensing material layers each formed at a different location on the semiconductor substrate;
Equipped with
the gas sensing material layer has a metal oxide layer and a catalytic metal layer formed on the metal oxide layer, the catalytic metal layer being exposed to the atmosphere;
the plurality of gas detection material layers are different from one another in combination of the type of material, thickness, and crystal grain size of the metal oxide layer, and the type of material, thickness, and crystal grain size of the catalytic metal layer;
Gas sensor chip.
2. The gas sensor chip according to claim 1,
a gate insulating film layer, a drain layer, a source layer, and a well are provided between the metal oxide layer and the semiconductor substrate, and the gas detection material layer is used as a gate layer for each of the plurality of gas detection material layers, thereby forming a plurality of sensor FETs.
Gas sensor chip.
3. The gas sensor chip according to claim 2,
In addition to the plurality of sensor FETs, a first FET having a gate layer configured to be isolated from the atmosphere.
Gas sensor chip.
3. The gas sensor chip according to claim 2,
A part of the plurality of sensor FETs is formed of an N-type FET, and another part of the plurality of sensor FETs is formed of a P-type FET.
Gas sensor chip.
3. The gas sensor chip according to claim 2,
each of the plurality of sensor FETs includes a silicon oxide film between the semiconductor substrate and the gate layer;
The thickness of the silicon oxide film in the plurality of sensor FETs is made to have a plurality of different thicknesses.
Gas sensor chip.
3. The gas sensor chip according to claim 2,
The plurality of sensor FETs include elements in which sensor FETs are connected in parallel or in series to each other.
Gas sensor chip.
3. The gas sensor chip according to claim 2,
the sensor FET includes a source terminal, a drain terminal, a well terminal, and a gate terminal;
At least one of the source terminal and the drain terminal is connected to an external power supply terminal for the gas sensor chip via a second FET having a gate layer isolated from the atmosphere.
Gas sensor chip.
3. The gas sensor chip according to claim 2,
In at least some of the plurality of sensor FETs, at least one of the metal oxide layer and the catalytic metal layer is formed of a plurality of layers.
Gas sensor chip.
3. The gas sensor chip according to claim 2,
At least some of the sensor FETs have a metal oxide layer doped with a catalytic metal or a catalytic metal layer doped with a metal oxide.
Gas sensor chip.
A gas sensor chip;
a heater section for heating and increasing the temperature of the gas sensor chip;
a control unit that controls the gas sensor chip and the heater unit;
Equipped with
The gas sensor chip includes:
A semiconductor substrate;
a plurality of gas-sensing material layers each formed at a different location on the semiconductor substrate;
Equipped with
the gas sensing material layer has a metal oxide layer and a catalytic metal layer formed on the metal oxide layer, the catalytic metal layer being exposed to the atmosphere;
the plurality of gas detection material layers are different from one another in combination of the type of material, thickness, and crystal grain size of the metal oxide layer, and the type of material, thickness, and crystal grain size of the catalytic metal layer;
the control unit controls the heater unit so that the gas sensor chip is at a predetermined temperature, and detects a gas in an atmosphere based on information obtained using the plurality of gas detection material layers.
Gas sensing systems.
11. The gas sensing system according to claim 10,
the gas sensor chip and the heater portion are each provided in a plurality of portions,
the heater units are disposed on the gas sensor chips, respectively;
the control unit controls the heater units so that the gas sensor chips have temperatures different from one another, and detects a gas in an atmosphere based on information obtained using the gas detection material layers in each of the gas sensor chips.
Gas sensing systems.
forming an impurity layer on a semiconductor substrate;
forming a first gas sensing material layer on the semiconductor substrate, the first gas sensing material layer including a catalytic metal layer;
forming a second gas sensing material layer including a catalytic metal layer on the semiconductor substrate at a position different from the first gas sensing material layer;
Including,
the first gas detection material layer and the second gas detection material layer are different from each other in at least one of the type of material constituting the gas detection material layer, the film thickness, and the crystal grain size;
A method for manufacturing a gas sensor chip.
13. The method for producing a gas sensor chip according to claim 12,
At least one of the steps of forming the first gas sensing material layer and the step of forming the second gas sensing material layer includes a step of forming a metal oxide layer.
A method for manufacturing a gas sensor chip.
13. The method for producing a gas sensor chip according to claim 12,
The steps of forming the first gas sensing material layer and forming the second gas sensing material layer include:
This is done in multiple deposition steps using masks.
A method for manufacturing a gas sensor chip.
14. The method for producing a gas sensor chip according to claim 13,
The step of forming the metal oxide layer includes a step of forming a metal layer and a step of oxidizing the formed metal layer.
A method for manufacturing a gas sensor chip.