DE102014223962A1 - Sensor pixel for detecting infrared radiation and method for operating the same - Google Patents

Abstract

The invention relates to sensor pixels (100) for detecting infrared radiation (102), wherein the sensor pixel (100) thermally decouples from a substrate (204) of the sensor pixel (100) absorber island (104) for absorbing the infrared radiation (102) and a metal Insulator semiconductor structure (106) which is part of the absorber island (104) and is adapted to image a temperature (112) of the absorber island (104) in an electrical signal (110).

Description

State of the art

The present invention relates to a sensor pixel for detecting infrared radiation, to a method for operating a sensor pixel for detecting infrared radiation, to a corresponding control device and to a corresponding computer program.

To register infrared radiation, there are two sensor principles. The first sensor principle is based directly on the detection of the photon using a cooled detector. As a result, a very high accuracy can be achieved, but the effort and energy consumption, especially for mobile devices is unacceptable and too expensive. The second sensor principle is based on the bolometric principle, ie the absorption of the photons and the detection of the resulting heat.

Disclosure of the invention

Against this background, with the approach presented here, a sensor pixel for detecting infrared radiation, a method for operating a sensor pixel for detecting infrared radiation, a control unit which uses this method, and finally a corresponding computer program according to the main claims are presented. Advantageous embodiments emerge from the respective subclaims and the following description.

According to the Planck Law, each object with a temperature around room temperature, ie in about 300 Kelvin (300 K), emits electromagnetic radiation with a focus in the far infrared range at wavelengths of about 8 microns to 14 microns. In this area, the absorption in the atmosphere is almost negligible, so that sensors can detect the radiation even over long distances and thus a conclusion on the object temperature can be drawn.

The bolometric principle allows uncooled operation of a temperature sensor. The conversion of the temperature signal into an electrically evaluable signal can be resistive, with thermocouples, pyroelectric or with suitable components such. As diodes occur. Since diodes do not require a switching matrix to select a single pixel and are also sensitive to temperature equalization signals, they can be used in microbolometers.

Since diodes block in a voltage direction, the current flows through only one pixel of the array with a suitable connection. Some principles, such as pyroelectric, only react to temperature changes. To create a thermal image, a "chopper" is used, which darkens the pixel again and again.

In order to increase the sensor sensitivity, either the design of the MEMS pixel can be optimized or the sensitivity of the component can be increased. In the case of diodes, the latter is technologically adjustable only within limits. For this reason, several diodes are combined in series to additively increase the temperature sensitivity. This results in a temperature sensitivity of about -2 mV / K per diode at constant current in the order of μA.

This inevitably also limits the miniaturization potential of the sensor. Since the optics, for example of milled germanium lenses, is the main cost driver of the system, there is a great interest in smaller pixels. With the same resolution, ie the same number of pixels, then a smaller and therefore cheaper optics can be used.

The approach presented here shows a possibility of generating the sensor signal by means of metal-insulator-semiconductor capacitances. The great advantage here is a very high miniaturization potential with simultaneously increased by three orders of magnitude temperature sensitivity compared to the previously used pn diodes.

The sensor presented here is based on the temperature-dependent tunnel current of a metal-insulator-semiconductor (Metal-Insulator-Semiconductor, MIS) layer stack. In this case, the insulator can consist of the oxide of the semiconductor and is preferably thinner than approximately 5 nm. The material system is then, for example, Si, SiO 2 and a metal, such as Al, for example. For materials with a higher dielectric constant (high k materials), the layer may be correspondingly thicker. In addition to the trouble-free full integration into the chip is the sensor presented here is characterized by a three orders of magnitude higher temperature sensitivity compared to conventional diodes.

The sensor presented here is predestined for use in far-infrared microbolometers. By using CMOS-compatible materials and the high miniaturization potential, it corresponds to the currently pursued low-cost approach with better performance than the currently used pn-diodes. Due to the significantly lower electrical operating point of less than 1 V compared to n times 0.7 V with n diodes in series, there is also the option to use a low-power ASIC process. This is particularly advantageous for mobile applications with limited energy storage.

Due to the enormous miniaturization potential of the components, virtually no limits are set for the pixel size apart from the absorption surface. A high temperature sensitivity is not dependent on the size of the component with skillful evaluation. This results in sensors with very small thermal mass, which consequently have very short reaction times. This is particularly advantageous for use in the automotive industry.

A sensor pixel for detecting infrared radiation is presented, wherein the sensor pixel has the following features:
an absorber island thermally decoupled from a substrate of the sensor pixel for absorbing the infrared radiation; and
a metal-insulator-semiconductor structure, which is part of the absorber island and is adapted to image a temperature of the absorber island in an electrical signal.

Furthermore, a method for operating a sensor pixel for detecting infrared radiation is presented, wherein the sensor pixel has an absorber island thermally decoupled from a substrate of the sensor pixel with a metal-insulator-semiconductor structure, the method comprising the following steps:
Evaluating an electrical signal of the metal-insulator-semiconductor structure using a processing rule to determine a temperature of the metal-insulator-semiconductor structure; and
Providing temperature information representing the temperature of the metal-insulator-semiconductor structure.

It can be evaluated with a constant current flow of the electrical signal to increase temperature sensitivity. Alternatively or additionally, can be evaluated with a constant voltage of the electrical signal to increase a temperature measuring range. This can be measured at a sensor pixel according to the approach presented here as needed with adapted measurement sequences.

Infrared radiation can be understood as electromagnetic radiation that has a greater wavelength than visible light. A sensor pixel may be a smallest detector unit of a sensor for the infrared radiation. The sensor may be imaging in conjunction with image forming optics. The sensor can image infrared radiation formed by the optics in image information. An absorber island can provide an absorption surface for the infrared radiation. A metal-insulator-semiconductor structure may be a semiconductor device. The metal-insulator semiconductor structure having stacked layers.

The metal-insulator semiconductor structure may comprise a metal layer, at least one insulator layer, and a semiconductor layer electrically insulated from the metal layer by the insulator layer. As a result, the sensor pixel can be produced inexpensively.

The metal-insulator-semiconductor structure may further comprise at least one further insulator layer. The further insulator layer may comprise a different insulator material than the insulator layer. In this case, the metal layer can be insulated from the semiconductor layer by the insulator layer and the further insulator layer. By the further insulator layer, an improved reliability of the sensor pixel can be achieved.

The absorber island may comprise a semiconductor material, which is formed as a semiconductor layer of the metal-insulator-semiconductor structure. By integrating the metal-insulator-semiconductor structure into the absorber island, a multiple use of the semiconductor material of the absorber island can be achieved. The semiconductor material then provides mechanical properties as a substrate and electrical properties for the metal-insulator-semiconductor structure.

The metal layer of the metal-insulator-semiconductor structure may be formed as a first electrical terminal for tapping the electrical signal of the metal-insulator-semiconductor structure. The metal layer may be referred to as an electrode of the semiconductor device.

The metal-insulator-semiconductor structure may include a second electrical terminal that is separated from the insulator layer by the semiconductor layer. The second electrical connection may be arranged on a side of the absorber island opposite the metal-insulator-semiconductor structure or arranged on the same side of the absorber island as the metal-insulator-semiconductor structure. The electrical signal can be tapped at the electrical terminals of the metal-insulator-semiconductor structure.

The metal-insulator-semiconductor structure can be configured in three dimensions. By structuring an enlarged surface can be provided. Due to the enlarged surface, a signal strength of the electrical signal can be increased.

The approach presented here also creates a control unit which is designed to execute, to control or to implement the steps of a variant of a method presented here in corresponding devices. Also by this embodiment of the invention in the form of a control device, the object underlying the invention can be achieved quickly and efficiently.

In the present case, a control device can be understood as meaning an electrical device which processes sensor signals and outputs control and / or data signals as a function thereof. The control unit may have an interface, which may be formed in hardware and / or software. In the case of a hardware-based design, the interfaces can be part of a so-called system ASIC, for example, which contains various functions of the control unit. However, it is also possible that the interfaces are their own integrated circuits or at least partially consist of discrete components. In a software training, the interfaces may be software modules that are present, for example, on a microcontroller in addition to other software modules.

Also of advantage is a computer program product or computer program with program code which can be stored on a machine-readable carrier or storage medium such as a semiconductor memory, a hard disk memory or an optical memory and for carrying out, implementing and / or controlling the steps of the method according to one of the embodiments described above is used, especially when the program product or program is executed on a computer or a device.

Tunnel-based CMOS-compatible temperature sensors are currently being used mainly in highly integrated circuits (ICs), such as B. processors used to detect spatially resolved overheating of the chip. Mainly due to the ongoing trend of miniaturization and the associated higher power density, thermal management is required.

The approach presented here will be explained in more detail below with reference to the accompanying drawings. Show it:

1 a block diagram of a sensor pixel for detecting infrared radiation according to an embodiment of the present invention;

2 Illustrations of a sensor pixel for detecting infrared radiation according to an embodiment of the present invention;

3 Illustrations of an absorber island with a metal-insulator-semiconductor structure according to an embodiment of the present invention;

4 an evaluation scheme for operating a sensor pixel according to an embodiment of the present invention;

5 a band diagram of a metal-insulator-semiconductor structure according to an embodiment of the present invention;

6 a characteristic field for evaluating an electrical signal of a metal-insulator semiconductor structure according to an embodiment of the present invention;

7 Representations of embodiments of a metal-insulator-semiconductor structure on an absorber island; and

8th a flowchart of a method for operating a sensor pixel for detecting infrared radiation according to an embodiment of the present invention.

In the following description of favorable embodiments of the present invention, the same or similar reference numerals are used for the elements shown in the various figures and similar acting, with a repeated description of these elements is omitted.

1 shows a block diagram of a sensor pixel 100 for detecting infrared radiation 102 according to an embodiment of the present invention. The sensor pixel 100 has a thermally decoupled absorber structure 104 and a temperature sensor 106 on. The sensor pixel 100 is designed to be an intensity 108 the infrared radiation 102 in an electrical signal 110 map. The absorber structure 104 is adapted to the infrared radiation 108 (after being focused on the array by optics, for example). By a thermal decoupling of the absorber structure 104 turns one from the intensity 108 dependent temperature 112 the absorber structure 104 one. The temperature sensor 106 is designed to the temperature 112 in the electrical signal 110 map. The temperature sensor 106 is as a layer stack 106 from a metal layer 114 , an insulator layer 116 and a semiconductor layer 118 formed, in which a tunnel current through the insulator layer is temperature dependent.

To the infrared radiation 102 on the absorber structure 104 can focus in an optical path of the sensor pixel 100 an optic 120 arranged here, for example, by a converging lens 120 is represented.

The electrical signal 110 the metal-insulator-semiconductor structure 106 has a stepless course within a predetermined value range. The electrical signal 110 can be referred to as analog signal. The electrical signal 110 is from a control unit 122 for operating the sensor pixel 100 read according to an embodiment of the present invention. In the control unit 122 becomes the electrical signal 110 evaluated to the temperature of the metal-insulator-semiconductor structure 106 and thus to the temperature 112 the absorption structure 104 zurückzuschließen. A value of temperature 112 is in a temperature information 124 from the controller 122 provided. The temperature information 124 is provided in the form of a digital signal in this embodiment.

In other words shows 1 a signal path at a bolometer 100 for Far Infrared Thermal Imaging Applications. It falls infrared radiation 102 (Incident IR) through an optic 120 (Optics) with an intensity 108 (P _th ) on a MEMS structure of the bolometer 100 , The infrared radiation 102 meets a mechanical absorption structure 104 (Mechanical IR Absorber MEMS Structure) and calls a temperature change 112 (ΔT). The temperature change 112 is based on a product of the intensity 108 and a thermal resistance of the absorbent structure 104 (ΔT = R _th P _th ). The temperature change 112 is due to a temperature-sensitive electrical component 106 (Electrical temperature sensitive device (TSD)) detected and in an electrical voltage change 110 (ΔV). The component 106 is a metal-insulator-semiconductor structure 106 (MIS Tunneling Capacitor). The voltage change 110 becomes an evaluation circuit 122 (ASIC) evaluated (read-out) and as digital temperature information 124 provided.

2 shows representations of a sensor pixel 100 for detecting infrared radiation 102 according to an embodiment of the present invention. Shown is a plan view of the sensor pixel 100 and a sectional view through the sensor pixel 100 , The sensor pixel 100 essentially corresponds to the sensor pixel in 1 , Here is the absorption structure 104 as absorber island 104 or absorption island 104 executed. When the infrared radiation 102 on the absorber island 104 falls, it is absorbed there. As long as through the infrared radiation 102 on the absorber island 104 incoming heat flow 200 is greater than one from the absorber island 104 outgoing total heat flow, increases a temperature of the absorber island 104 , When the incoming heat flow 200 is smaller than the outgoing total heat flow, the temperature of the absorber island is reduced 104 ,

The absorber island 104 is by a beam structure 202 on a substrate 204 of the sensor pixel 100 suspended. The beam structure 202 bridges a gap 206 between the substrate 204 and the absorber island 104 , The gap 206 is, for example, gas-filled with air or a noble gas. This decouples the gap 206 due to the low thermal conductivity of gas the absorber island 104 thermally from the substrate 204 , About the gap can only a very small first heat flow 208 from the absorber island 104 flow away.

The beam structure 202 has two little arms 210 . 212 with a great thermal resistance. This can cause a very low second heat flow 214 from the absorber island 104 in the direction of the substrate 204 or in the opposite direction.

In this embodiment, the arms are 210 . 212 spiral around the absorber island 104 executed. The little arms 210 . 212 can also be designed meandering. Due to the spiral or meandering design, the arms show 210 . 212 a long length relative to its cross-sectional area. This results in the large thermal resistance.

A third heat flow 216 flows due to direct radiation from the absorber island 104 from. All three outgoing heat flows 208 . 214 . 216 give the total heat flow and are in equilibrium with the incoming heat flow 200 through the infrared radiation 102 when the temperature of the absorber island 104 is constant.

In the arms 210 . 212 are electrical leads 218 for the metal-insulator-semiconductor structure 106 integrated. The metal-insulator-semiconductor structure 106 is part of the absorber island 104 ,

In one embodiment, the microbolometer has pixels 100 a SiO2 absorber 104 on a silicon island (Si Island). The silicon island and the absorber 104 are from the substrate 204 (Bulk Si) thermally isolated.

The metal-insulator-semiconductor structure 106 can be applied to a pixel made with MEMS processes 100 be applied, which additionally contains an infrared absorber. The MEMS process is based on standard available semiconductor industry process steps. The process may involve a special procedure for cutting thin retainer sleeves 210 . 212 be supplemented, at which the pixel 100 is suspended.

The arrangement of individual pixels 100 in a matrix is easily possible. Manufacturing tolerances can be compensated by calibration at a reference temperature, for example, when the system is turned on. By calibration, for example, it is no longer the absolute current that acts as the measurement signal, but the current gain, based on the calibrated value.

3 shows representations of an absorber island 104 with a metal-insulator-semiconductor structure 106 according to an embodiment of the present invention. Shown is a sectional view through the absorber island 104 and a plan view of the absorber island 104 , The absorber island 104 corresponds essentially to the absorber island in 2 , In addition, here is an embodiment of the metal-insulator-semiconductor structure 106 with their layers 114 . 116 . 118 and the electrical leads 218 shown. The metal-insulator-semiconductor structure 106 extends over a large part of a surface of the absorber island 104 , The metal layer 114 is the first electrical connection 300 the metal-insulator-semiconductor structure 106 directly with one of the supply lines 218 connected. A second electrical connection 302 the metal-insulator-semiconductor structure 106 is in a corner of the absorber island 104 arranged and with the other electrical supply line 218 connected. The second electrical connection 302 is on the same side of the absorber island 104 arranged as the metal-insulator-semiconductor structure 106 , The second electrical connection 302 is designed as a further metal layer and by a gap 304 from the metal-insulator-semiconductor structure 106 separated.

The absorber island 104 has a semiconductor material 306 on. The semiconductor material 306 is for the most part weakly positively endowed. In one area 308 below the second electrical connection 302 is the semiconductor material 306 positively endowed. The insulator layer 116 the metal-insulator-semiconductor structure 106 is directly on the semiconductor material 306 the absorber island 104 arranged. The semiconductor material 306 So is the semiconductor layer 118 the metal-insulator-semiconductor structure 106 , This is the absorber island 104 integral part of the metal-insulator-semiconductor structure 106 ,

The metal-insulator-semiconductor structure 106 here has another insulator layer 310 on. The further insulator layer 310 is made of a different insulator material than the insulator layer 116 , In this embodiment, the insulator layer 116 of silicon dioxide, while the further insulator layer 310 from hafnia. The further insulator layer 310 is between the insulator layer 116 and the metal layer 114 arranged.

In the approach presented here will be at least one metal-insulator-semiconductor (MIS) tunnel capacitance 106 as a temperature-sensitive element 106 on a microbolometer pixel 100 used. For making one or more thin oxide layers 116 to the particular lightly predoped epi-silicon 118 and an overlying metallization 114 applied. The cropping of the pixels 100 takes place, for example, chemically. Sensiergröße is either the tunnel current or the current gain based on the tunnel current at a reference temperature or the voltage at a constant impressed current. This achieves a high miniaturization potential and a signal which is temperature-sensitive by three orders of magnitude compared to the sensor principle currently based on pn diodes.

The MIS tunnel capacity 106 becomes in the epitaxially grown silicon 306 brought in. This is done by implantation of the bulk contact 308 into the weakly p-doped Epi-Si 306 , The insulator layer results from a standard gate oxidation or by deposition of one or more oxide layers 116 and 310 , The formation of the second contact is effected by full-surface metal deposition and metal structuring.

In 3 an exemplary layout is shown in cross-section and plan view. In other words shows 3 a cross section and a top view of the tunnel MIS structure 106 , The bulk contact (B) 308 is highly doped to make an ohmic contact 302 provide. The gate contact (G) 300 With its surface automatically determines the height of the tunnel current and is accordingly larger.

In the illustrated embodiment, a SiO 2 / HfO 2 layer system is used to prevent leakage currents through the very thin SiO 2. This results in the end increased reliability. Physically, a simple SiO 2 layer is sufficient to implement the sensor principle.

Unlike diodes, the MIS tunnels are capacities 106 not self-locking, so an extra switch matrix is needed to make one pixel 100 from a plurality of pixels 100 select. However, this can save space as a pn diode in series either on the pixel 100 even realized, which is possible due to the very small sensor element or in one below the MEMS element 104 level on the ASIC. Then, the switching matrix may be constructed, for example, of MOSFETs.

4 shows an evaluation scheme 400 for operating a sensor pixel 100 according to an embodiment of the present invention. The evaluation scheme 400 is on a control unit 122 for operating the sensor pixel 100 executed. The control unit 122 has a facility 402 to evaluate and a device 404 to deploy. The device 402 for evaluation is designed to be an electrical signal 110 the metal-insulator-semiconductor structure 106 evaluate to a temperature 112 the metal-insulator-semiconductor structure 106 to determine. The device 404 for providing is adapted to a temperature information 124 provide a value of the temperature 112 the metal-insulator-semiconductor structure 106 represents. In one embodiment, the temperature information becomes 124 provided as a digital signal.

The illustrated evaluation scheme 400 has two different evaluation paths 406 . 408 on. The evaluation paths 406 . 408 are each connected by a switch between the electrical supply line 218 and the respective path 406 . 408 switchable.

In the first evaluation path 406 becomes a value of electric current flow 410 (I _G ) of the electrical signal 110 at a constant voltage 412 (V _GB ) of the electrical signal 110 evaluated. Thereby the value of the electric current flow becomes 410 measured while the sensor pixel 100 the constant electrical voltage 412 is imprinted.

In the second evaluation path 408 becomes a value of electrical voltage 412 at a constant electric current flow 410 evaluated. This is the value of the electrical voltage 412 measured while the sensor pixel 100 the constant electric current flow 410 is impressed.

In both evaluation paths 406 . 408 is calculated using its own processing rule from the measured value 410 . 412 to the temperature 112 the metal-insulator-semiconductor structure 106 closed. In the first evaluation path 406 The first processing specification describes a temperature-current characteristic of the metal-insulator-semiconductor structure 106 , In the second evaluation path 408 The second processing specification describes a temperature-voltage characteristic of the metal-insulator-semiconductor structure 106 ,

In one embodiment, the first processing rule represents a relationship between the electrical current flow 410 the electrical signal 110 and the temperature 112 at constant voltage 412 , The second processing rule represents a relationship between the voltage 412 the electrical signal 110 and the temperature 112 at constant current flow 410 , Using the first processing protocol, high sensitivity is achieved. Using the second processing instruction, a large measurement range is achieved.

In one embodiment, a common processing rule represents a family of characteristics of the metal-insulator-semiconductor structure 106 , The characteristic field forms the electrical voltage 412 the electrical signal 110 , the electric current flow 410 the electrical signal 110 and the temperature 112 from.

The construction can be done with slight modifications using epi-silicon 306 respectively. Instead of operating several diodes in series as before, a single sensor element is sufficient due to the high temperature sensitivity 106 off to a sufficiently large electrical signal 110 to create. Because it is a bipolar device 100 are acting on each pixel 100 two electrical lines 218 led to the outside to the component 100 with the ASIC 122 connect to. This is particularly advantageous because of the low number of lines 218 the thermal decoupling of the pixel 100 minimized and thus the sensor performance is positively influenced.

In other words shows 4 an evaluation concept for an ASIC 122 with switchable signal evaluation. In the first evaluation path 406 becomes the electricity 412 as evaluation signal at constant voltage 410 used. In the second evaluation path 408 becomes the tension 410 as evaluation signal at constant current 412 used.

5 shows a band diagram 500 a metal-insulator-semiconductor structure according to an embodiment of the present invention. In the band diagram 500 are different energy levels 502 . 504 . 506 . 508 (E _FM , E _C , E _F , E _V ) of electrons within the metal-insulator-semiconductor structure. In this case, the electrons are on a first side of the insulator layer 116 a low energy level 502 on. On an opposite second side of the insulator layer 116 the electrons have higher energy levels 504 . 506 . 508 on. The electrons tunnel through the insulator layer 116 why they have jumps in energy level.

In principle, the temperature effect is as follows: An applied electric field between gate electrode and bulk Si causes an inversion charge under the oxide 116 generated, as indicated by the electron shown in the band diagram. The oxide 116 is so constructed or is so thin that each carrier through the oxide 116 can tunnel to the electrode. Tunneling is a quantum mechanical process that describes the passage of a charge carrier through classically forbidden states of energy. This includes, for example, a thin, non-conductive layer 116 , If the current is limited in this case by the provision of the charge carriers and not by the tunneling probability, results in a quadratically increasing with the temperature saturation current, which can be used as a temperature signal.

In other words shows 5 a band diagram of the system Al / SiO2 / Si (p-doped) with tunneling electrons through the oxide 116 ,

6 shows a characteristic field 600 for evaluating an electrical signal of a metal-insulator-semiconductor structure according to an embodiment of the present invention. The characteristic field 600 is plotted on a graph plotted on the abscissa voltage in volts (V) and plotted on the ordinate a charge density in ampere per square centimeter (A / cm2). In this case, the electrical voltage represents the voltage between the electrical terminals of the metal-insulator-semiconductor structure, as shown in the 1 to 4 is shown. As the temperature of the metal-insulator-semiconductor structure increases, the charge density increases. This is due to a variety of characteristics 602 expressed as associated with a temperature of the metal-insulator-semiconductor structure as shown.

mit der Boltzmann Konstante k, der effektiven Elektronenmasse m_eff, der Elementarladung q, der reduzierten Planck Konstante h, der absoluten Temperatur T, der Tunnelwahrscheinlichkeit T_n, der Schottky Barrierenhöhe ϕ_B, dem Dioden Idealitätsfaktor m und der Bulk-Gate-Spannung V_BG. Bei negativem Gatepotenzial (also V_BG > 0 V) entspricht diese Formel nahezu der klassischen Diodengleichung. Es kommt hier zu einer Anreicherung von Löchern unter dem Oxid. Weder die Löcherkonzentration im Si noch die Elektronenkonzentration im Metall sind temperaturabhängig. Daher eignet sich dieser Arbeitspunkt auch nicht zur Temperaturmessung.The current-voltage characteristic 600 can be done in principle by solving the Schrödinger equation using the Wentzel-Kramer-Brillouin (WKB) method with rectangular potential barrier. It turns out

with the Boltzmann constant k, the effective electron mass m _eff , the elementary charge q, the reduced Planck constant h, the absolute temperature T, the tunneling probability T _n , the Schottky barrier height φ _B , the diode ideality factor m, and the bulk gate voltage V _BG . With a negative gate potential (ie V _BG > 0 V), this formula corresponds almost to the classical diode equation. It comes here to an accumulation of holes under the oxide. Neither the hole concentration in the Si nor the electron concentration in the metal are temperature-dependent. Therefore, this operating point is not suitable for temperature measurement.

Only in the case of an inversion, ie an accumulation of minority charge carriers and V _BG <0 V, which corresponds to a positive gate potential, is the quadratic temperature dependence usable for a temperature measurement.

By way of example, the temperature-dependent measurement shown here results. How to get in 6 shown, a temperature increase by 10 K leads to about a doubling of the current.

In other words shows 6 a temperature-dependent current-voltage characteristic of an MIS tunnel structure with 2 nm thick SiO2.

An evaluation of the current at constant voltage as shown by the vertical arrow is particularly suitable when a large temperature variation is expected. This can be the case in the case of a microbolometer application, for example, for very high signals, such as in the monitoring of a laser beam or the fire detection of the case. With only low temperature strokes it is more suitable to measure the voltage at constant current, as shown by the horizontal arrow. This results in temperature sensitivities of up to -5.5 V / K. Thus, a sensor pixel according to the approach presented here by the factor 2750 is more sensitive than a single pn junction.

Since only temperature strokes of the order of magnitude of μK can be expected on the pixel in micro-bolometric images of scenes around 300 K, for example for thermal images in night vision systems, a second evaluation concept is to be preferred for these applications. To cover both applications, the control unit presented here can switch between "constant current" and "constant voltage". Either solution may be sufficient and is still significantly better than established systems.

7 shows illustrations of embodiments of a metal-insulator-semiconductor structure 106 on an MIS structure 104 according to the approach presented here. The metal-insulator-semiconductor structure 106 with the MIS structure 104 is essentially the same as in 3 , In contrast, the second electrical connection 302 each on one, the metal-insulator-semiconductor structure 106 opposite side of the absorber island 104 arranged. The absorber would be on top or below. The reference number 104 here denotes weakly doped Si, which is only very weakly absorbing IR.

In the embodiment shown on the right side, the metal-insulator-semiconductor structure is 106 structured in three dimensions to provide a larger surface for generating the electrical signal and thus a larger signal amplitude of the electrical signal.

The technically interesting area of the device 106 As a gate stack can be realized in many design variants. There are implementation possibilities of the Gatestapels 106 on the Epi-Si 104 shown. The right structure 106 has an increased tunneling current due to the larger interface of Si and SiO2.

8th shows a flowchart of a method 800 for operating a sensor pixel for detecting infrared radiation according to an embodiment of the present invention. The method can be used on a control unit, such as in 4 is shown to be executed. The method has one step 802 the evaluation and a step 804 of providing. In step 802 of the evaluation, an electrical signal of the metal-insulator-semiconductor structure is evaluated using a processing instruction. The evaluation determines a temperature of the metal-insulator-semiconductor structure. In step 804 the provision of temperature information is provided which represents the temperature of the metal-insulator-semiconductor structure.

The embodiments described and shown in the figures are chosen only by way of example. Different embodiments may be combined together or in relation to individual features. Also, an embodiment can be supplemented by features of another embodiment.

Furthermore, the method steps presented here can be repeated as well as executed in a sequence other than that described.

If an exemplary embodiment comprises a "and / or" link between a first feature and a second feature, then this is to be read so that the embodiment according to one embodiment, both the first feature and the second feature and according to another embodiment either only first feature or only the second feature.

Claims (13)

Sensor pixel ( 100 ) for detecting infrared radiation ( 102 ), where the sensor pixel ( 100 ) has the following features: a thermal from a substrate ( 204 ) of the sensor pixel ( 100 ) decoupled absorber island ( 104 ) for absorbing the infrared radiation ( 102 ); and a metal-insulator-semiconductor structure ( 106 ), which are part of the absorber island ( 104 ) and is adapted to a temperature ( 112 ) of the absorber island ( 104 ) in an electrical signal ( 110 ). Sensor pixel ( 100 ) according to claim 1, wherein the metal-insulator-semiconductor structure ( 106 ) a metal layer ( 114 ), at least one insulator layer ( 116 ) and one through the insulator layer ( 116 ) of the metal layer ( 114 ) electrically insulated semiconductor layer ( 118 ). Sensor pixel ( 100 ) according to claim 2, wherein the metal-insulator-semiconductor structure ( 106 ) further at least one further insulator layer ( 310 ), which comprises a different insulator material, than the insulator layer ( 116 ), wherein the metal layer ( 114 ) through the insulator layer ( 116 ) and the further insulator layer ( 310 ) from the semiconductor layer ( 118 ) is isolated. Sensor pixel ( 100 ) according to one of the preceding claims, wherein the absorber island ( 104 ) a semiconductor material ( 306 ), which as semiconductor layer ( 118 ) of the metal-insulator-semiconductor structure ( 106 ) is trained. Sensor pixel ( 100 ) according to one of the preceding claims, in which the metal layer ( 114 ) of the metal-insulator-semiconductor structure ( 106 ) as a first electrical connection ( 300 ) for picking up the electrical signal ( 110 ) of the metal-insulator-semiconductor structure ( 106 ) is trained. Sensor pixel ( 100 ) according to claim 5, wherein the metal-insulator-semiconductor structure ( 106 ) a second electrical connection ( 302 ) passing through the semiconductor layer ( 118 ) of the insulator layer ( 116 ), the second electrical connection ( 302 ) on one, the metal-insulator-semiconductor structure ( 106 ) opposite side of the absorber island ( 104 ) is arranged. Sensor pixel ( 100 ) according to claim 5, wherein the metal-insulator-semiconductor structure ( 106 ) a second electrical connection ( 302 ) passing through the semiconductor layer ( 118 ) of the insulator layer ( 116 ), the second electrical connection ( 302 ) on the same side of the absorber island ( 104 ), such as the metal-insulator-semiconductor structure ( 106 ). Sensor pixel ( 100 ) according to one of the preceding claims, in which the metal-insulator-semiconductor structure ( 100 ) is executed three-dimensionally structured. Procedure ( 800 ) for operating a sensor pixel ( 100 ) for detecting infrared radiation ( 102 ), where the sensor pixel ( 100 ) thermally from a substrate ( 204 ) of the sensor pixel ( 100 ) decoupled absorber island ( 104 ) with a metal-insulator-semiconductor structure ( 106 ), the method ( 800 ) has the following steps: evaluating ( 802 ) of an electrical signal ( 110 ) of the metal-insulator-semiconductor structure ( 106 ) using a processing protocol to obtain a temperature ( 112 ) of the metal-insulator-semiconductor structure ( 106 ) to determine; and Provide ( 804 ) a temperature information ( 124 ), which determines the temperature ( 112 ) of the metal-insulator-semiconductor structure ( 106 ). Procedure ( 800 ) according to claim 9, wherein in step ( 802 ) of the evaluation with a constant current flow ( 410 ) of the electrical signal ( 110 ) is evaluated in order to increase a temperature sensitivity and / or with a constant voltage ( 412 ) of the electrical signal ( 110 ) is evaluated to increase a temperature measuring range. Control unit ( 122 ), which is designed to handle all steps of a process ( 800 ) for operating a sensor pixel ( 100 ) according to one of the preceding claims. Computer program adapted to perform all the steps of a method according to any one of the preceding claims. A machine-readable storage medium having a computer program stored thereon according to claim 12.

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