CN113640361A - Grid sensitive FET gas sensor array for trace formaldehyde gas detection and preparation method thereof - Google Patents

Grid sensitive FET gas sensor array for trace formaldehyde gas detection and preparation method thereof Download PDF

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CN113640361A
CN113640361A CN202110813558.1A CN202110813558A CN113640361A CN 113640361 A CN113640361 A CN 113640361A CN 202110813558 A CN202110813558 A CN 202110813558A CN 113640361 A CN113640361 A CN 113640361A
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sensitive
grid
layer
gate
fet
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张勇
刘灿
张志勇
曹觉先
关笑笑
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Xiangtan University
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Xiangtan University
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    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
    • G01N27/00—Investigating or analysing materials by the use of electric, electrochemical, or magnetic means
    • G01N27/26—Investigating or analysing materials by the use of electric, electrochemical, or magnetic means by investigating electrochemical variables; by using electrolysis or electrophoresis
    • G01N27/403—Cells and electrode assemblies
    • G01N27/414—Ion-sensitive or chemical field-effect transistors, i.e. ISFETS or CHEMFETS
    • G01N27/4141—Ion-sensitive or chemical field-effect transistors, i.e. ISFETS or CHEMFETS specially adapted for gases
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
    • G01N27/00—Investigating or analysing materials by the use of electric, electrochemical, or magnetic means
    • G01N27/26—Investigating or analysing materials by the use of electric, electrochemical, or magnetic means by investigating electrochemical variables; by using electrolysis or electrophoresis
    • G01N27/403—Cells and electrode assemblies
    • G01N27/414—Ion-sensitive or chemical field-effect transistors, i.e. ISFETS or CHEMFETS
    • G01N27/4146—Ion-sensitive or chemical field-effect transistors, i.e. ISFETS or CHEMFETS involving nanosized elements, e.g. nanotubes, nanowires
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01L—SEMICONDUCTOR DEVICES NOT COVERED BY CLASS H10
    • H01L21/00—Processes or apparatus adapted for the manufacture or treatment of semiconductor or solid state devices or of parts thereof
    • H01L21/70—Manufacture or treatment of devices consisting of a plurality of solid state components formed in or on a common substrate or of parts thereof; Manufacture of integrated circuit devices or of parts thereof
    • H01L21/77—Manufacture or treatment of devices consisting of a plurality of solid state components or integrated circuits formed in, or on, a common substrate
    • H01L21/78—Manufacture or treatment of devices consisting of a plurality of solid state components or integrated circuits formed in, or on, a common substrate with subsequent division of the substrate into plural individual devices
    • H01L21/82—Manufacture or treatment of devices consisting of a plurality of solid state components or integrated circuits formed in, or on, a common substrate with subsequent division of the substrate into plural individual devices to produce devices, e.g. integrated circuits, each consisting of a plurality of components
    • H01L21/8206—Manufacture or treatment of devices consisting of a plurality of solid state components or integrated circuits formed in, or on, a common substrate with subsequent division of the substrate into plural individual devices to produce devices, e.g. integrated circuits, each consisting of a plurality of components the substrate being a semiconductor, using diamond technology
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01L—SEMICONDUCTOR DEVICES NOT COVERED BY CLASS H10
    • H01L27/00—Devices consisting of a plurality of semiconductor or other solid-state components formed in or on a common substrate
    • H01L27/02—Devices consisting of a plurality of semiconductor or other solid-state components formed in or on a common substrate including semiconductor components specially adapted for rectifying, oscillating, amplifying or switching and having at least one potential-jump barrier or surface barrier; including integrated passive circuit elements with at least one potential-jump barrier or surface barrier
    • H01L27/04—Devices consisting of a plurality of semiconductor or other solid-state components formed in or on a common substrate including semiconductor components specially adapted for rectifying, oscillating, amplifying or switching and having at least one potential-jump barrier or surface barrier; including integrated passive circuit elements with at least one potential-jump barrier or surface barrier the substrate being a semiconductor body
    • H01L27/08—Devices consisting of a plurality of semiconductor or other solid-state components formed in or on a common substrate including semiconductor components specially adapted for rectifying, oscillating, amplifying or switching and having at least one potential-jump barrier or surface barrier; including integrated passive circuit elements with at least one potential-jump barrier or surface barrier the substrate being a semiconductor body including only semiconductor components of a single kind
    • H01L27/085—Devices consisting of a plurality of semiconductor or other solid-state components formed in or on a common substrate including semiconductor components specially adapted for rectifying, oscillating, amplifying or switching and having at least one potential-jump barrier or surface barrier; including integrated passive circuit elements with at least one potential-jump barrier or surface barrier the substrate being a semiconductor body including only semiconductor components of a single kind including field-effect components only
    • H01L27/088—Devices consisting of a plurality of semiconductor or other solid-state components formed in or on a common substrate including semiconductor components specially adapted for rectifying, oscillating, amplifying or switching and having at least one potential-jump barrier or surface barrier; including integrated passive circuit elements with at least one potential-jump barrier or surface barrier the substrate being a semiconductor body including only semiconductor components of a single kind including field-effect components only the components being field-effect transistors with insulated gate

Abstract

The invention provides a grid sensitive FET gas sensor array for detecting trace formaldehyde gas, which comprises: an array substrate; a plurality of formaldehyde gas sensors prepared on the basic surface of the array through a semiconductor process, wherein the formaldehyde gas sensors are grid sensitive sensors and are periodically distributed; wherein, the grid sensitive sensor comprises an FET sensor taking a carbon nano tube as a channel, and sequentially comprises: a channel layer composed of Carbon Nanotubes (CNTs); a dielectric layer over the channel layer; the dielectric layer is positioned between the source electrode and the drain electrode; and the sensitive layer is positioned between the source electrode and the drain electrode and is formed above the dielectric layer and used as a grid electrode, and the sensitive layer is a precious metal sensitive layer which is continuously distributed. The grid sensitive FET gas sensor array can realize accurate detection of trace formaldehyde gas in complex environments with various gases, such as common air environments.

Description

Grid sensitive FET gas sensor array for trace formaldehyde gas detection and preparation method thereof
Technical Field
The invention relates to the technical field of formaldehyde sensors, in particular to a grid sensitive FET gas sensor array for trace formaldehyde gas detection and a preparation method thereof.
Background
Formaldehyde (HCHO), widely present in building materials, decorative materials, wood furniture and carpets, is one of the most important pollutants in indoor environmental Volatile Organic Compounds (VOCs) and is considered to be the main cause of pathogenic building syndrome (SBS). Formaldehyde is a highly dangerous Volatile Organic Compound (VOC) gas that can cause skin poisoning, leukemia, and respiratory canceration. Urea formaldehyde resins, an important binder in everyday decorative materials, slowly release formaldehyde gas over a period of decades. According to the regulation of the national sanitary Standard for Formaldehyde in the air of the Living room, the maximum allowable concentration of formaldehyde in the air of the Living room is 0.08mg/m3(-80 ppb). With the increasing standard of living, the need for effective detection and degradation of HCHO gas in indoor air has become very urgent.
At present, the resistance type semiconductor gas sensor has become a gas sensor with the largest yield and the widest application range due to the advantages of low cost, simple manufacture, high sensitivity and the like. Research workers at home and abroad develop research work on high-performance resistance type gas sensors aiming at single HCHO and other indoor decoration pollution main harmful gases. However, the research on the accurate detection of trace HCHO gas in a complex gas environment is rarely reported because the resistive gas sensor has the defect of similar response to different gases and has higher cross sensitivity, and the essential reason is that the parameters of the resistive device are too single, the influence of the gases on sensitive materials can be reflected only by means of resistivity, and the change of the gas type and concentration can cause the change of the resistivity, so that the classification identification and the accurate detection of the sensor on the gas type and concentration are restricted.
Although the sensitivity to a single gas can be improved by technologies such as nano-functionalization or surface functionalization of a sensitive material, when ppb-level trace gas is detected, the response signal is small, the interference of factors such as other gases is easy to occur, and the detection of a weak signal can be realized only by a large working current or voltage. The resistance type gas sensor is difficult to improve applicability and reliability in a multi-component complex gas environment in principle, practical application of the gas sensor to detection of trace formaldehyde gas in the complex gas environment is restricted, and the main obstacle is that the resistivity is the only parameter and expression form of gas-sensitive performances such as evaluation selection characteristics, sensitivity characteristics and the like of the sensor.
Disclosure of Invention
The invention aims to provide a grid sensitive FET gas sensor array for detecting trace formaldehyde gas and a preparation method thereof, which can realize accurate detection of the trace formaldehyde gas in complex environments with various gases (such as common air environments).
According to a first aspect of the present invention, there is provided a gate sensitive FET gas sensor array for trace formaldehyde gas detection, comprising:
an array substrate;
a plurality of formaldehyde gas sensors prepared on the basic surface of the array through a semiconductor process, wherein the formaldehyde gas sensors are grid sensitive sensors and are periodically distributed;
wherein, the grid sensitive sensor comprises an FET sensor taking a carbon nano tube as a channel, and sequentially comprises:
a channel layer composed of Carbon Nanotubes (CNTs);
a dielectric layer over the channel layer;
the dielectric layer is positioned between the source electrode and the drain electrode; and
and the sensitive layer is positioned between the source electrode and the drain electrode and formed above the dielectric layer and is used as a grid electrode, the sensitive layer is a precious metal sensitive layer which is continuously distributed, and the thickness of the sensitive layer is 1 nm-10 nm.
Preferably, the dielectric layer is an yttrium oxide dielectric layer, and the thickness of the dielectric layer is between 6nm and 12 nm.
Preferably, the thickness of the channel layer is 1nm to 2 nm.
Preferably, the source electrode and the drain electrode are Ti/Au electrodes, and the thickness is 50 nm-60 nm.
Preferably, the precious metal sensitive layer is a palladium-gold alloy sensitive layer, and comprises a palladium thin film layer in contact with the dielectric layer and a gold thin film layer positioned above the palladium thin film layer.
Preferably, the gate sensitive FET gas sensor array is set to an operating voltage of 10V in operation and is set to detect induced trace formaldehyde gas at room temperature of 25 ℃ or heated to 150 ℃.
Preferably, the periodic distribution comprises an array periodic distribution, that is, a plurality of grid sensitive sensors are distributed in a horizontal row and a vertical row, and a grid of each grid sensitive sensor is connected to a common grid PAD to form a signal transmission layer for leading out a sensing signal.
Preferably, the periodic distribution includes that even number N of gate-sensitive sensors form a combination and are sequentially arranged in a straight line in four crossed directions; the grid electrode and the drain electrode of the grid electrode sensitive sensor in each direction are led out independently and are arranged in a direction vertical to the arrangement line of the grid electrode sensitive sensors along the line; the grid electrodes of the grid electrode sensitive sensors in each direction are led out together and extend to the positions of the lead-out directions of the grid electrodes and the drain electrodes; a plurality of said combinations are distributed in an array to form an array of gate sensitive FET gas sensors.
According to the second aspect of the invention, a method for preparing a grid sensitive type FET gas sensor array for detecting trace formaldehyde gas is also provided, which comprises the following steps:
step 1, cleaning a carbon nanotube film substrate;
step 2, forming a source electrode and a drain electrode of each grid sensitive type sensor in the grid sensitive type FET gas sensor array on the cleaned carbon nano tube film substrate, and preparing a Pd/Au source electrode and a drain electrode with certain thickness on the carbon nano tube film substrate through an evaporation process respectively;
step 3, etching the carbon nanotube film substrate, and removing redundant carbon nanotubes by etching on the premise of keeping the carbon nanotubes of each grid sensitive sensor as a channel layer;
step 4, preparing an yttrium oxide dielectric layer with a double-layer structure on the carbon nano tube channel layer of each grid sensitive sensor and between the source electrode and the drain electrode;
step 5, preparing a precious metal sensitive layer which is continuously distributed between the drain electrode and the source electrode and above the yttrium oxide dielectric layer to be used as a grid electrode; the precious metal sensitive layer comprises one of metal simple substances Pd, Au and Cr, or one of alloy alloys Pd/Au, Pd/Cr, Au/Cr and Pd/Au/Cr; and
and 6, connecting the grid of each grid sensitive type sensor to a public grid PAD to form a signal transmission layer for leading out a sensing signal, and thus preparing the grid sensitive type FET gas sensor array for detecting the trace formaldehyde gas.
Preferably, the thickness of the yttrium oxide dielectric layer is controlled to be 6 nm-12 nm, and the thickness of the carbon nano tube channel layer is controlled to be 1 nm-2 nm; the thickness of the noble metal sensitive layer is controlled to be 1 nm-10 nm.
It should be understood that all combinations of the foregoing concepts and additional concepts described in greater detail below can be considered as part of the inventive subject matter of this disclosure unless such concepts are mutually inconsistent. In addition, all combinations of claimed subject matter are considered a part of the presently disclosed subject matter.
The foregoing and other aspects, embodiments and features of the present teachings can be more fully understood from the following description taken in conjunction with the accompanying drawings. Additional aspects of the present invention, such as features and/or advantages of exemplary embodiments, will be apparent from the description which follows, or may be learned by practice of specific embodiments in accordance with the teachings of the present invention.
Drawings
The drawings are not intended to be drawn to scale. In the drawings, each identical or nearly identical component that is illustrated in various figures may be represented by a like numeral. For purposes of clarity, not every component may be labeled in every drawing. Embodiments of various aspects of the present invention will now be described, by way of example, with reference to the accompanying drawings, in which:
FIG. 1a is a schematic flow chart of a process for preparing a gate sensitive FET gas sensor array for trace formaldehyde gas detection according to an exemplary embodiment of the present invention.
FIG. 1b is a schematic structural diagram of a gate-sensitive sensor in a gate-sensitive FET gas sensor array for trace formaldehyde gas detection according to an exemplary embodiment of the present invention.
Fig. 2a, 2b are schematic diagrams of gate sensitive FET gas sensor arrays for trace formaldehyde gas detection according to exemplary embodiments of the invention.
FIG. 3 is a schematic diagram of a gate sensitive FET gas sensor array for trace formaldehyde gas detection in accordance with an exemplary embodiment of the invention in accordance with another embodiment of the invention.
FIG. 4 is a schematic representation of atomic force microscopy characterization of a gate sensitive FET gas sensor array.
FIG. 5 is a schematic diagram of an electrical performance test of a gate sensitive FET gas sensor array.
FIG. 6 is a schematic diagram of a gas sensing performance test of a gate sensitive FET gas sensor array.
Fig. 7 is a schematic diagram of the transient response of a gate sensitive FET gas sensor array at different operating voltages.
FIG. 8 is a schematic diagram of transient response at different operating temperatures of an array of gate sensitive FET gas sensors.
FIG. 9 is a graph showing the results of a gas selectivity test of an array of gate sensitive FET gas sensors.
FIG. 10 is a schematic diagram of a response performance test of a gate sensitive FET gas sensor array.
FIG. 11 is a schematic diagram of a moisture resistance test of a gate sensitive FET gas sensor array.
FIG. 12 is a schematic diagram of a transfer curve for a gate sensitive FET gas sensor array.
FIG. 13 is a graph showing transient response test results of an array of gate sensitive FET gas sensors at different sensitive layer thicknesses.
Detailed Description
In order to better understand the technical content of the present invention, specific embodiments are described below with reference to the accompanying drawings.
In this disclosure, aspects of the present invention are described with reference to the accompanying drawings, in which a number of illustrative embodiments are shown. Embodiments of the present disclosure are not necessarily intended to include all aspects of the invention. It should be appreciated that the various concepts and embodiments described above, as well as those described in greater detail below, may be implemented in any of numerous ways, as the disclosed concepts and embodiments are not limited to any one implementation. In addition, some aspects of the present disclosure may be used alone, or in any suitable combination with other aspects of the present disclosure.
With reference to fig. 1a, an exemplary embodiment of the present invention provides a gate-sensitive FET gas sensor array for trace formaldehyde gas detection, which includes an array substrate and a plurality of formaldehyde gas sensors prepared by a semiconductor process on a basic surface of the array, wherein the formaldehyde gas sensors are gate-sensitive sensors, and the plurality of formaldehyde gas sensors are periodically distributed.
With reference to the example shown in fig. 1b, the gate-sensitive sensor comprises a FET sensor with a carbon nanotube as the channel, comprising in sequence: a channel layer composed of Carbon Nanotubes (CNTs); a dielectric layer over the channel layer; the dielectric layer is positioned between the source electrode and the drain electrode; and the sensitive layer is positioned between the source electrode and the drain electrode and formed above the dielectric layer and is used as a grid electrode, the sensitive layer is a precious metal sensitive layer which is continuously distributed, and the thickness of the sensitive layer is 1 nm-10 nm.
Preferably, the precious metal sensitive layer comprises one of Pd, Au and Cr of simple metal or one of the alloy of Pd/Au, Pd/Cr, Au/Cr and Pd/Au/Cr of the alloy. Therefore, through the selected metal simple substance or the selected alloy of the common body, the formaldehyde gas molecules are catalyzed into small molecules, the charge density of the surface of the grid electrode is easy to change, and the formaldehyde gas is easy to detect.
In the following examples, an exemplary Pd/Au alloy is exemplified. In an alternative embodiment, the noble metal sensitive layer is a palladium-gold alloy sensitive layer (Pd/Au) including a palladium thin film layer in contact with the dielectric layer and a gold thin film layer over the palladium thin film layer.
Wherein the CNT channel layer of each sensor cell (i.e., one gate-sensitive sensor) has an aspect ratio of 2, wherein in the following examples, the length is 25 microns and the width is 50 microns.
Preferably, the dielectric layer is a yttria dielectric layer, i.e. Y2O3The film has a thickness of 6nm to 12 nm.
Preferably, the CNT channel layer is made of semiconductor carbon nanotubes with a thickness of 1nm to 2nm and a CNT purity of 99.9% or more, and a commercially available high-purity CNT thin film substrate can be used, for example.
Preferably, the source electrode and the drain electrode are Ti/Au electrodes, and the thickness is 50 nm-60 nm.
Preferably, the gate sensitive FET gas sensor array is set to an operating voltage of 10V in operation and is set to detect induced trace formaldehyde gas at room temperature of 25 ℃ or heated to 150 ℃.
Preferably, the periodic distribution includes an array periodic distribution, that is, a plurality of gate-sensitive sensors are distributed in a row and column manner, and a gate of each gate-sensitive sensor is connected to a common gate PAD to form a signal transmission layer for leading out a sensing signal, as shown in fig. 2a and 2 b.
Preferably, the periodic distribution includes that even number N of gate-sensitive sensors form a combination and are sequentially arranged in a straight line in four crossed directions; the grid electrode and the drain electrode of the grid electrode sensitive sensor in each direction are led out independently and are arranged in a direction vertical to the arrangement line of the grid electrode sensitive sensors along the line; the grid electrodes of the grid electrode sensitive sensors in each direction are led out together and extend to the positions of the lead-out directions of the grid electrodes and the drain electrodes; a plurality of said combinations form an array of gate sensitive FET gas sensors in an arrayed distribution, as shown in figure 3.
According to the second aspect of the invention, the invention also provides a preparation method of the grid sensitive type FET gas sensor array for detecting the trace formaldehyde gas, which comprises the following steps:
step 1, cleaning a carbon nanotube film substrate;
step 2, forming a source electrode and a drain electrode of each grid sensitive type sensor in the grid sensitive type FET gas sensor array on the cleaned carbon nano tube film substrate, and preparing a Pd/Au source electrode and a drain electrode with certain thickness on the carbon nano tube film substrate through an evaporation process respectively;
step 3, etching the carbon nanotube film substrate, and removing redundant carbon nanotubes by etching on the premise of keeping the carbon nanotubes of each grid sensitive sensor as a channel layer;
step 4, preparing an yttrium oxide dielectric layer with a double-layer structure on the carbon nano tube channel layer of each grid sensitive sensor and between the source electrode and the drain electrode;
step 5, preparing a precious metal sensitive layer which is continuously distributed between the drain electrode and the source electrode and above the yttrium oxide dielectric layer to be used as a grid electrode;
and 6, connecting the grid of each grid sensitive type sensor to a public grid PAD to form a signal transmission layer for leading out a sensing signal, and thus preparing the grid sensitive type FET gas sensor array for detecting the trace formaldehyde gas.
Preferably, the thickness of the yttrium oxide dielectric layer is controlled to be 6 nm-12 nm, and the thickness of the carbon nano tube channel layer is controlled to be 1 nm-2 nm; the thickness of the noble metal sensitive layer is controlled to be 1 nm-10 nm.
We take Pd/Au gate sensitive layer as an example to describe more specifically the preparation process of the gate sensitive FET gas sensor array of the present invention.
(1) And cleaning the carbon nano tube film substrate by adopting an electron beam evaporation and oxidation process. The 4-inch carbon nanotube film substrate was purchased from Beijing Hua carbon core electronics, Inc.
The detailed steps are as follows: in an ultraclean room environment (the air contains dust particles with the diameter of 0.5 mu m less than 1000), a diamond pen is used for dividing the 4-inch carbon nanotube film substrate into two 2-inch substrates. And evaporating 3nm yttrium metal on a 2-inch carbon nanotube film substrate by adopting an electron beam evaporation process (an electron beam coating instrument DE400 DHL).
In the ultra-clean compartment (air contains dust particle number less than 100 with diameter of 0.5 μm), the substrate is placed on a hot plate heated to 270 deg.C, and the metal yttrium on the surface of the carbon nanotube film substrate is oxidized in air atmosphere for 30min to form yttrium oxide (Y)2O3)。
Removing redundant metal yttrium and Y on the surface of the carbon nano tube film substrate2O3Adhering impurities.
The detailed steps are as follows: in the ultra-clean compartment region, the surface contains Y2O3Soaking the carbon nanotube film substrate in hydrochloric acid solution H for 1min2O: the HCl ratio is 20: 1. and respectively washing the surface of the carbon nano tube film substrate by using ethanol, acetone, deionized water and an isopropyl acetone solution in the front and the back. And finally blowing the mixture by using nitrogen.
(2) And forming a source electrode and a drain electrode of each FET unit in the array on the cleaned carbon nano tube film substrate by adopting laser direct writing and electron beam evaporation processes (namely, first photoetching).
The detailed steps are as follows: in the ultra-clean ten-thousand-level yellow light region, photoresists LOR and S1813 are coated on the carbon nanotube film substrate in a front-back rotating mode, a laser direct writing machine (model MicroWriter ML) is used for exposing the source electrode region and the drain electrode region of each FET unit, and the used layout is shown in figure 3. The exposed carbon nanotube film substrate was then kept in a DEVELOPER solution (model MICROPOSIT MF-39 DEVELOPER) for 1min and fixed in deionized water for 1 min. And finally blowing the mixture by using nitrogen.
And respectively evaporating Ti/Pd/Au with the thickness of 0.3-1nm/20nm/60nm on the carbon nano tube film substrate subjected to photoetching by adopting an electron beam evaporation process in an ultraclean room environment.
In the ultra-clean spacer region, the carbon nanotube film substrate plated with the Ti/Pd/Au metal film is soaked in a PG solution (model G0502004000L 1PE) for about 12 hours and then is washed with IPA for 2 minutes. And finally blowing the mixture by using nitrogen.
(3) Using laser direct writing and O2And a plasma etching process for etching away redundant carbon nanotubes so as to ensure that the carbon nanotubes exist in the channel of each FET unit.
The detailed steps are as follows: photoresist LOR and S1813 are coated on the carbon nano tube film substrate in a ten thousand-level yellow light area in an ultraclean way in a front-back spin mode, and the area except the channel area of each FET unit is exposed by a laser direct writing machine. And then strictly keeping the exposed carbon nanotube film substrate in a developing solution for 1min, and strictly keeping the exposed carbon nanotube film substrate in deionized water for 1 min. And finally blowing the mixture by using nitrogen.
In an ultra-clean room environment, O is adopted2Plasma etching (RIE) process (plasma etcher model LIVELL PLASMA), and subjecting the carbon nanotube film substrate to O etching2The plasma reacts with the exposed areas of carbon nanotubes for 60s, etching the redundant carbon nanotubes to ensure that carbon nanotubes remain only in each channel.
And in a ten thousand-level area between ultra-clean rooms, putting the etched carbon nanotube film substrate into a PG solution to be soaked for about 0.5-1h, and respectively washing the surface of the carbon nanotube film substrate with ethanol, acetone, deionized water and an isopropanol solution from front to back. And finally blowing the mixture by using nitrogen.
(4) Forming Y on the carbon nanotube film in the channel region by direct laser writing, electron beam evaporation and oxidation2O3A dielectric layer.
The detailed steps are as follows: photoresist LOR and S1813 are coated on the carbon nano tube film substrate in a ten thousand-level yellow light area in an ultraclean way in a front-back spin mode, and the area except the channel area of each FET unit is exposed by a laser direct writing machine. And then strictly keeping the exposed carbon nanotube film substrate in a developing solution for 1min, and strictly keeping the exposed carbon nanotube film substrate in deionized water for 1 min. And finally blowing the mixture by using nitrogen.
And evaporating 3nm metal yttrium on the carbon nanotube film substrate after photoetching by adopting an electron beam evaporation process in an ultra-clean room environment.
In a super clean spacer region, the carbon nano tube film substrate plated with the metal yttrium is placed into a PG solution to be soaked for about 0.5-1h, and then is washed for 2 minutes by IPA. Blow-drying with nitrogen. Placing the blow-dried substrate on a hot plate heated to 270 deg.C, oxidizing metal yttrium on the surface of the carbon nanotube film substrate in air atmosphere for 30min to form yttrium oxide (Y)2O3)。
(5) In this embodiment, the dielectric layer of the gate-sensitive carbon-based FET array uses a double layer Y2O3. And (4) repeating the step (4).
(6) And forming a sensitive layer between the source electrode and the drain electrode and above the dielectric layer by adopting laser direct writing and electron beam evaporation processes.
The detailed steps are as follows: photoresist LOR and S1813 are coated on the carbon nano tube film substrate in a ten thousand-level yellow light area in an ultraclean way in a front-back spin mode, and the area except the channel area of each FET unit is exposed by a laser direct writing machine. And then strictly keeping the exposed carbon nanotube film substrate in a developing solution for 1min, and strictly keeping the exposed carbon nanotube film substrate in deionized water for 1 min. And finally blowing the mixture by using nitrogen.
And evaporating a 1-10 nm metal sensitive layer on the carbon nano tube film substrate subjected to photoetching by adopting an electron beam evaporation process in an ultra-clean room environment. The metal sensitive layer comprises metal simple substances Pd, Au and Cr and alloys Pd/Au, Pd/Cr, Au/Cr and Pd/Au/Cr.
In a super clean room ten thousand-level area, the carbon nano tube film substrate plated with the metal sensitive layer is placed into a PG solution to be soaked for about 0.5 to 1 hour, and then is washed for 2 minutes by IPA. Blow-drying with nitrogen.
(7) The gate of each FET cell is connected to a common gate Pad for forming a signal transmission layer using laser direct writing and electron beam evaporation processes.
The detailed steps are as follows: photoresist LOR and S1813 are coated on the carbon nano tube film substrate in a ten thousand-level yellow light area in an ultraclean way in a front-back spin mode, and the area except the channel area of each FET unit is exposed by a laser direct writing machine. And then strictly keeping the exposed carbon nanotube film substrate in a developing solution for 1min, and strictly keeping the exposed carbon nanotube film substrate in deionized water for 1 min. And finally blowing the mixture by using nitrogen.
And (3) evaporating 40nm Au on the carbon nano tube film substrate subjected to photoetching by adopting an electron beam evaporation process in an ultra-clean room environment.
And finally, putting the carbon nanotube film substrate plated with the signal transmission layer into a PG solution to be soaked for about 12 hours, and then washing the substrate for 2 minutes by using IPA. Blow-drying with nitrogen.
And finally obtaining the gate sensitive type carbon-based FET array.
In the embodiment of the invention, the thickness of the used carbon nanotube film substrate is 2nm, the purity reaches more than 99.9%, and the carbon nanotubes in the carbon nanotube film substrate are overlapped and randomly distributed to assemble a network film.
FIG. 4 is an atomic force microscope characterization diagram of the sensor array, wherein (a) is the surface topography of the Au thin film layer in the sensitive layer; (b) the height distribution diagram of the source and drain electrodes Ti/Au; (c) the height distribution diagram of the grid sensitive layer Pd/Au; (d) gate dielectric layer Y2O3The height profile of (a). In the embodiment of the invention, the grid sensitive layer is evaporated to form a continuous noble metal film by an electron beam, and the surface topography of the top sensitive layer Au is shown in the figure. As can be seen from the figure, the surface of the sensor has a certain roughness, which is tested to be 0.79nm, and can provide adsorption sites for gas molecules, so that the reaction of the material and the gas molecules is facilitated, and the response of the gas sensor is improved. As can be seen from (b) to (d) of FIG. 4, the source and drain electrodes, and the sensitive layers Pd/Au and Y2O3The thicknesses of the dielectric layers were 50, 20, 6.03nm, respectively.
FIG. 5 is an exemplary representation of the electrical performance of a sensor array, wherein (a) is a schematic diagram of the electrical connections of a sensor device under test; (b) is a dielectric layer Y2O3Transfer curves of devices after processing; the inset is the transfer curve of the device with only carbon nanotubes in the channel; (c) the transfer curve of the device after the Pd/Au process is carried out on the grid of the sensitive layer; (d) the output curve of the device is the output curve when only the carbon nano tube exists in the channel; (e) is an output curve of the device after the Pd/Au process of the sensitive layer grid; (f) in order to introduce 800ppb formaldehyde gasAnd the output curve pair (Vgs is 0V, Vds is 10V) of the front and back devices. From the test results, it can be seen that the transfer characteristic of the p-type transistor characteristic is maintained throughout the sensor during the continuous fabrication process, which has little effect on the channel material characteristics. Note that, with the dielectric layer Y2O3Due to the introduction of the film and the sensitive layer Pd/Au film, the working voltage of a single sensor device is reduced by one order of magnitude from-1V to-0.1V, and the power consumption of the device is effectively reduced. FIG. 4(d-e) shows the output characteristics of the sensor devices before and after the introduction of the Pd/Au thin film as the sensitive layer. After the Pd/Au thin film is introduced, the device presents a very obvious Schottky contact, and the Schottky contact is favorable for obtaining a larger response of the sensor. The effect of gas injection on the electrical properties of the devices was further investigated and fig. 4(f) shows the output characteristics of FET devices exposed to 800ppb HCHO. The conductance of the device changes after the HCHO gas is exposed, which shows that the device is sensitive to HCHO gas molecules and has the possibility and performance basis of being applied to a formaldehyde gas sensor.
Fig. 6 shows the gas sensitivity test results of the grid-sensitive carbon-based sensor array to formaldehyde gas under different working conditions. Wherein graph (a) is a dynamic response curve of the gas sensor at room temperature; the inset is a concentration-response fit of the gas sensor at room temperature; (b) is a repeatability curve of the gas sensor at room temperature; (c) is the dynamic response curve of the gas sensor at 150 ℃; the inset is a fit of the response of the gas sensor in different formaldehyde concentrations; (d) the repeatability curve of the gas sensor at 150 ℃ is shown. From the surface of the test results, in conjunction with fig. 5(a), in the absence of heating (i.e., at room temperature of 25 ℃), the resistance of the gas sensor gradually increased with an increase in the formaldehyde concentration, showing P-type response behavior. Under the heating condition of 150 ℃, as shown in fig. 5(c), the resistance of the gas sensor gradually increases with the increase of the formaldehyde concentration, and an N-type response behavior is shown, in the process, the increase of the temperature causes the change of the material carrier concentration, so that the gas sensitivity of the device to the formaldehyde gas is improved. Therefore, the common baseline drift problem under the room-temperature working condition is effectively solved by heating, the detection limit of the HCHO is as low as 10ppb, and the response-concentration linear correlation coefficient is greatly improved from 0.86 (at room temperature) to 0.99 (after heating). The repetitive tests of fig. 5(b) and 5(d) further illustrate that heating improves its sensing performance, increasing recovery of HCHO from 80% to 97%.
Fig. 7 shows the transient response test results of the gate-sensitive carbon-based sensor array at different operating voltages. The gas-sensitive performance of the device under different working voltage registration is compared and tested, and the result of the graph shows that the grid-sensitive carbon-based formaldehyde gas sensor array has the best gas-sensitive response when the working voltage is 10V, and the optimal working voltage is determined to be 10V.
Fig. 8 shows a graph of the transient response of the gate-sensitive carbon-based sensor array at different operating temperatures. As shown, the test temperature conditions for each of the figures are: (a)25 ℃; (b)50 ℃; (c)75 ℃; (d)100 ℃; (e) at 150 ℃. Graph (f) is a temperature-response comparison graph.
From the test results, the gate sensitive carbon-based FET array gas sensor has the best transient response at an operating temperature of 150 ℃, and the optimal operating temperature is determined to be 150 ℃.
FIG. 9 shows results of selective testing of gate-sensitive carbon-based sensor arrays for different gases. We performed comparative tests at 25 degrees celsius and 150 degrees celsius. Wherein the test temperature conditions for each of the figures are: (a)25 ℃; (b) at 150 ℃. From the test results, the selectivity of different gases has the best gas sensitive response to formaldehyde gas at 25 ℃ and 150 ℃. Therefore, the sensor shows high selectivity to formaldehyde gas and does not change with the change of external conditions.
FIG. 10 is a schematic diagram of a response performance test of a gate sensitive FET gas sensor array. The graph (a) and the graph (b) are response values, response times/recovery times of the gate-sensitive formaldehyde gas sensor in 3 dynamic response/recovery processes at 25 ℃ and 150 ℃, respectively. It can be seen from the figure that, by changing the working conditions, the gas-sensitive response, the response time and the recovery time of the device to formaldehyde gas are basically consistent, and the stability is good.
FIG. 11 is a schematic diagram of a moisture resistance test of a gate-sensitive carbon-based sensor array. Panel (a) is a moisture resistance test; (b) is a long term stability test result. According to long-term test results, the sensor array prepared by the method has better moisture resistance and long-term stability.
FIG. 12 is a graph illustrating transfer curves for a gate-sensitive carbon-based sensor array. Wherein, the graph (a) is the transfer curve of 90 sensor units in the grid-sensitive carbon-based formaldehyde gas sensor array when only the carbon nanotube film is in the channel before the process; (b) is at Y2O3Transfer curve of 90 cells after dielectric layer process. It can be seen that in increasing Y2O3After the dielectric layer process, the consistency of the electrical performance of the device is obviously improved.
Fig. 13 is a schematic diagram of transient response test results of the gate-sensitive carbon-based sensor array at different sensitive layer thicknesses. Wherein graph (a) is a graph of the transient response of a FET array gas sensor with different sensitive materials of 10nm thickness as the sensitive gate; graph (b) is a graph of the transient response of a FET array gas sensor with different sensitive materials of 1nm thickness as the sensitive gate; graph (c) is a repeated plot of FET devices with different sensitive materials of 10nm thickness as the sensitive gate; graph (d) is a repeated plot of different sensitive materials as sensitive gate FET devices at 1nm thickness. As can be seen from the test of fig. 13, the transient response of the gate-sensitive carbon-based sensor array shows better consistency under the condition of the sensitive layers with the thicknesses of 1nm and 10 nm.
Although the present invention has been described with reference to the preferred embodiments, it is not intended to be limited thereto. Those skilled in the art can make various changes and modifications without departing from the spirit and scope of the invention. Therefore, the protection scope of the present invention should be determined by the appended claims.

Claims (10)

1. A gate-sensitive FET gas sensor array for trace formaldehyde gas detection, comprising:
an array substrate;
a plurality of formaldehyde gas sensors prepared on the basic surface of the array through a semiconductor process, wherein the formaldehyde gas sensors are grid sensitive sensors and are periodically distributed;
wherein, the grid sensitive sensor comprises an FET sensor taking a carbon nano tube as a channel, and sequentially comprises:
a channel layer composed of carbon nanotubes;
a dielectric layer over the channel layer;
the dielectric layer is positioned between the source electrode and the drain electrode; and
and the sensitive layer is positioned between the source electrode and the drain electrode and formed above the dielectric layer and is used as a grid electrode, the sensitive layer is a precious metal sensitive layer which is continuously distributed, and the thickness of the sensitive layer is 1 nm-10 nm.
2. The gate-sensitive FET gas sensor array for trace formaldehyde gas detection according to claim 1, wherein the dielectric layer is a yttria dielectric layer having a thickness of between 6nm and 12 nm.
3. The gate-sensitive FET gas sensor array for trace formaldehyde gas detection according to claim 1, wherein the thickness of the channel layer is 1nm to 2 nm.
4. The gate-sensitive FET gas sensor array for trace formaldehyde gas detection according to claim 1, wherein the source and drain electrodes are Ti/Au electrodes and have a thickness of 50nm to 60 nm.
5. The gate-sensitive FET gas sensor array for trace formaldehyde gas detection according to claim 1, wherein the noble metal sensitive layer is a palladium-gold alloy sensitive layer comprising a palladium thin film layer in contact with a dielectric layer and a gold thin film layer over the palladium thin film layer.
6. The gate-sensitive FET gas sensor array for trace formaldehyde gas detection as claimed in claim 1, wherein the gate-sensitive FET gas sensor array is set to an operating voltage of 10V during operation and is set to detect induced trace formaldehyde gas at room temperature of 25 ℃ or heated to 150 ℃.
7. The gate sensitive FET gas sensor array for trace formaldehyde gas detection according to any one of claims 1-6, wherein the periodic distribution comprises an array periodic distribution, that is, a plurality of gate sensitive sensors are arranged in a row and column, and the gate of each gate sensitive sensor is connected to a common gate PAD to form a signal transmission layer for leading out a sensing signal.
8. The grid-sensitive FET gas sensor array for trace formaldehyde gas detection according to any one of claims 1-6, wherein the periodic distribution comprises an even number N of grid-sensitive sensors forming a combination, and the grid-sensitive FET gas sensors are sequentially arranged in a straight line in four crossed directions; the grid electrode and the drain electrode of the grid electrode sensitive sensor in each direction are led out independently and are arranged in a direction vertical to the arrangement line of the grid electrode sensitive sensors along the line; the grid electrodes of the grid electrode sensitive sensors in each direction are led out together and extend to the positions of the lead-out directions of the grid electrodes and the drain electrodes; a plurality of said combinations are distributed in an array to form an array of gate sensitive FET gas sensors.
9. A method for preparing a gate sensitive FET gas sensor array for trace formaldehyde gas detection as claimed in claim 1, comprising the steps of:
step 1, cleaning a carbon nanotube film substrate;
step 2, forming a source electrode and a drain electrode of each grid sensitive type sensor in the grid sensitive type FET gas sensor array on the cleaned carbon nano tube film substrate, and preparing a Pd/Au source electrode and a drain electrode with certain thickness on the carbon nano tube film substrate through an evaporation process respectively;
step 3, etching the carbon nanotube film substrate, and removing redundant carbon nanotubes by etching on the premise of keeping the carbon nanotubes of each grid sensitive sensor as a channel layer;
step 4, preparing an yttrium oxide dielectric layer with a double-layer structure on the carbon nano tube channel layer of each grid sensitive sensor and between the source electrode and the drain electrode;
step 5, preparing a precious metal sensitive layer which is continuously distributed between the drain electrode and the source electrode and above the yttrium oxide dielectric layer to be used as a grid electrode; the precious metal sensitive layer comprises one of metal simple substances Pd, Au and Cr, or one of alloy alloys Pd/Au, Pd/Cr, Au/Cr and Pd/Au/Cr;
and 6, connecting the grid of each grid sensitive type sensor to a public grid PAD to form a signal transmission layer for leading out a sensing signal, and thus preparing the grid sensitive type FET gas sensor array for detecting the trace formaldehyde gas.
10. The method for preparing the gate-sensitive FET gas sensor array for trace formaldehyde gas detection according to claim 9, wherein the thickness of the dielectric layer of yttrium oxide is controlled to be 6 nm-12 nm, and the thickness of the channel layer of carbon nanotubes is controlled to be 1 nm-2 nm; the thickness of the noble metal sensitive layer is controlled to be 1 nm-10 nm.
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