JP2010164550A - Infrared radiation element, infrared gas detector equipped with the same, and method of manufacturing infrared radiation element - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an infrared radiation element that has high output, is capable of performing high-frequency drive, and has low power consumption, and to provide a method of manufacturing the infrared radiation element. <P>SOLUTION: The infrared radiation element includes a semiconductor substrate 1; a holding layer 2 formed on one surface of the semiconductor substrate 1; a gas layer 3 consisting of a space surrounded by one surface of the semiconductor substrate 1 and that of the holding layer 2; a support section 4 for connecting one surface of the substrate 1 to that of the holding layer 2 inside the gas layer 3 and supporting the holding layer 2; and an infrared radiation layer 5, that is laminated on the other surface of the holding layer 2 and radiates infrared rays due to the heat generated by electrical input. The thickness of the gas layer 3 is set, according to the frequency of voltage applied to the infrared radiation layer 5, and the gas layer works as a heat-insulating layer and a heat-radiating layer, when the temperature of the infrared radiation layer 5 rises and when the infrared radiation layer 5 is lowered, respectively. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to an infrared radiation element, an infrared gas detector equipped with the infrared radiation element, and a method of manufacturing the infrared radiation element.

  Conventionally, infrared rays are received through an infrared emitting element that emits infrared rays, and a filter that passes only infrared rays having a wavelength that is absorbed by the detection target gas among infrared rays emitted from the infrared emitting elements. There is a gas sensor device including a light receiving element that outputs a detection signal of a level corresponding to the amount of infrared rays. And the said infrared radiation element radiates | emits an infrared ray intermittently in multiple times by one measurement. At that time, in order to increase detection accuracy and save power, it is desirable to stabilize the amount of infrared radiation radiated from the infrared radiation element and to measure it in a short time. It is rare.

  As the infrared radiation element, a bulb-type infrared radiation element 40 as shown in FIG. 11 and a diaphragm-type infrared radiation element 50 as shown in FIG. 12 are provided (for example, see Patent Document 1).

  In the bulb-type infrared radiation element 40, the filament 42 of the light emitting part is formed by winding a wire made of tungsten (W) or platinum (Pt) in a coil shape, or the coil surface is coated with a ceramic such as alumina. It is configured. And when a voltage is applied to the filament 42 and the temperature rises, infrared rays are emitted. In addition, since the infrared radiation element 40 has a large heat capacity of the filament 42 serving as a light emitting unit, the time from when the voltage is applied to the filament 42 until the intensity of the emitted infrared radiation reaches a predetermined intensity (temperature increase time) Is long. Moreover, the time (temperature decrease time) from when the applied voltage of the filament 42 emitting infrared rays is turned off until the emission of infrared rays stops is long. Therefore, in order to increase the amplitude difference between the infrared rays that are intermittently radiated, it is necessary to set the frequency of the voltage applied to the filament 42 to about 0.1 to 10 Hz.

  Further, the diaphragm-type infrared radiation element 50 has a recess 52 formed by etching a semiconductor substrate 51 provided on the back surface of the infrared radiation layer 50 by etching. The infrared radiation layer 50 includes an insulating layer 55 including a heat generating layer 53 connected to an electrode 56 made of metal and a light emitting layer 54 indirectly heated by the heat generating layer 53. The light emitting layer 54 emits infrared rays by being indirectly heated by the heat generated by the heat generating layer 53 to which a voltage is applied via the electrode 56. Moreover, since the diaphragm type infrared radiation element 50 is insulated by the heat insulation effect of the air which the insulating layer 55 contacts in the recessed part 52, the temperature rising time of the light emitting layer 54 is short. However, due to the heat insulation effect, the light emitting layer 54 cannot obtain a sufficient heat dissipation effect, so the temperature drop time is long. Therefore, in order to increase the difference in the amplitude of the infrared rays emitted intermittently, it is necessary to set the frequency of the voltage applied to the electrode 56 to about 200 Hz, for example.

JP-A-9-184757

  Therefore, when the infrared radiating element 40 or the infrared radiating element 50 is used in a gas sensor device or the like, the modulation frequency of the input voltage applied to the infrared radiating element is low, the measurement takes time, and the power consumption is reduced. It was difficult to do.

  The present invention has been made in view of the above-described reasons, and an object of the present invention is to provide an infrared radiation element capable of high output and high frequency driving and low power consumption, and an infrared gas provided with the infrared radiation element. It is in providing a detector and its manufacturing method.

  The invention of claim 1 includes a semiconductor substrate, a thin holding layer formed on one surface of the semiconductor substrate, a gas layer comprising a space surrounded by one surface of the semiconductor substrate and the one surface of the holding layer, and the holding layer. And an infrared radiation layer that emits infrared rays by heat generated by electrical input, and the gas layer has a thickness set based on a frequency of a voltage applied to the infrared radiation layer, and emits infrared radiation. It functions as a heat-insulating layer when the temperature of the layer is raised, and as a heat dissipation layer when the temperature of the infrared radiation layer is lowered.

  According to the present invention, in the infrared radiation element, when the temperature of the infrared radiation layer is increased, the heat transmitted from the infrared radiation layer to the holding layer is insulated by the gas layer. Gas that acts as a heat dissipation layer because the heat transfer time from the infrared radiation layer to the holding layer is dissipated to the semiconductor substrate through the gas layer when the temperature of the infrared radiation layer is lowered and the temperature rise time is shortened. The layer reduces the temperature drop time of the infrared radiation layer. Therefore, the temperature of the infrared radiation layer is raised and lowered at a high speed, and the infrared radiation element can be driven at a high output and a high frequency. Further, the measurement time can be shortened and the power consumption can be reduced.

  The invention of claim 2 is characterized in that, in the invention of claim 1, the gas layer is provided with a support portion for connecting the semiconductor substrate and the holding layer and supporting the holding layer.

  According to the present invention, the retention layer can be prevented from adhering to the semiconductor substrate due to the difference in thermal expansion due to the temperature rise and fall of the infrared radiation layer, the temperature rise inhibition and damage can be prevented, and the drying after the wet treatment during production It is possible to prevent the holding layer from adhering to the semiconductor substrate.

  According to a third aspect of the present invention, in the second aspect of the present invention, the support portion is made of single crystal silicon.

  According to the present invention, by using single crystal silicon having a higher mechanical strength than the porous layer for the support portion, the holding layer adheres to the semiconductor substrate due to the difference in thermal expansion due to the temperature rise and fall of the infrared radiation layer. Further, it is possible to more effectively prevent the holding layer from adhering to the semiconductor substrate during drying after the wet treatment at the time of manufacture. In particular, when the substrate is formed of single crystal silicon and the support portion is formed of single crystal silicon with a part of the support portion remaining, the stress generated at the connection portion between the support portion and the substrate is zero and the strength of the support portion is further increased. Become more effective.

  According to a fourth aspect of the present invention, in the invention of the second or third aspect, an infrared radiation layer is laminated at a plurality of locations on the other surface of the retaining layer, and a support portion is provided on one surface side of the retaining layer exposed between the infrared radiation layers. It is provided.

  According to this invention, since the infrared radiation layer having a higher thermal conductivity than the holding layer is not in direct contact with the support portion, the heat generated in the infrared radiation layer is radiated to the semiconductor substrate side through the support portion. This can be suppressed, and the luminous efficiency of the infrared radiation layer can be increased.

  In addition, since the infrared radiation layer and the support portion are not in direct contact with each other, it is possible to suppress the occurrence of a large temperature gradient between the infrared radiation layer and the support portion, and the infrared radiation is caused by the large thermal stress caused by the temperature gradient. It can prevent that a layer and a support part break.

  According to a fifth aspect of the present invention, in the invention according to any one of the first to fourth aspects, the holding layer comprises a porous layer.

  According to the present invention, since the porous layer has a smaller heat capacity and thermal conductivity than a dense insulating material, the temperature rise time can be shortened without hindering the temperature rise of the infrared radiation layer, and the temperature rises greatly with small energy. By doing so, low power consumption can be achieved.

  The invention of claim 6 is the invention of claim 5, wherein the porous layer is made of porous silicon or porous polysilicon.

  According to this invention, since it consists of porous layer porous silicon or porous polysilicon, it is possible to ensure heat resistance that can withstand the temperature rise of the infrared radiation layer.

  According to a seventh aspect of the present invention, in the invention according to any one of the first to sixth aspects, the periphery of the holding layer is fixed to a semiconductor substrate.

  According to the present invention, since the holding layer has all the peripheral edge bonded to the semiconductor substrate and the holding strength is increased, the holding layer is deformed by the thermal expansion difference generated when the infrared radiation layer bonded to the holding layer is heated and lowered. Can be prevented from being damaged.

  The invention of claim 8 is characterized in that, in the invention of claim 7, the portion where the semiconductor substrate and the holding layer are joined includes a reinforcing portion for reinforcing the joining of the holding layer and the semiconductor substrate.

  According to this invention, the strength of the joint between the holding layer and the semiconductor substrate can be increased, and damage due to deformation of the holding layer can be further prevented.

According to a ninth aspect of the present invention, in the invention according to any one of the first to eighth aspects, the holding layer has a thermal conductivity smaller than that of the semiconductor substrate, and the heat transfer from the infrared radiation layer accompanying energization of the infrared radiation layer is one. The infrared radiation is emitted in the direction toward the infrared radiation layer by at least one of the temperature rise of the part and the reflection of the infrared radiation incident from the infrared radiation layer, and the infrared radiation layer has a function of passing the infrared radiation radiated from the holding layer It is characterized by having.
According to the present invention, part of the energy radiated from the infrared radiation layer toward the holding layer is used as the energy of the infrared radiation, and the infrared radiation efficiency with respect to the input power can be increased. In other words, it leads to a reduction in input power necessary to emit desired infrared rays.

The invention of claim 10 is the invention according to any one of claims 1 to 9, wherein the thickness dimension of the holding layer is such that when the refractive index is n and the film thickness is d, the optical path length with respect to the infrared ray of the target wavelength is the infrared ray. The optical film thickness nd is set to be a natural number multiple of a half wavelength.
According to the present invention, the resonance condition is established in the holding layer for the infrared ray of the target wavelength, and the relative radiation intensity can be increased for the infrared ray of the target wavelength. In this embodiment, it is desirable to provide the support portion according to claim 2 in order to prevent thermal deformation of the holding layer due to heat generation.

According to an eleventh aspect of the present invention, in the invention according to any one of the first to tenth aspects, the holding layer has macropores that radiate infrared rays by cavity emission during heating formed in a bulk semiconductor, and nanopores are formed in the macropores. It is a structure.
According to the present invention, infrared radiation efficiency can be increased by utilizing cavity radiation by macropores. In addition, since the nanopores are formed in the macropores, it is possible to compensate for the decrease in strength of the holding layer that accompanies the formation of the macropores without inhibiting the cavity radiation by the macropores. Furthermore, by using a porous semiconductor having nanopores in the macropores for the holding layer, high heat insulating performance can be obtained in the holding layer.

According to a twelfth aspect of the present invention, in the invention according to any one of the first to tenth aspects, the holding layer is formed of an electrical insulating film containing a semiconductor oxide.
According to this invention, since the holding layer can be formed by oxidizing the semiconductor by a process such as thermal oxidation or performing CVD of the material containing the oxide, the manufacturing process is relatively simple, The mass productivity can be increased as compared with the case of making it porous.

According to a thirteenth aspect of the present invention, in the invention according to any one of the first to twelfth aspects, the infrared radiation element is formed of a material having a negative resistance temperature coefficient.
According to the present invention, even if the driving voltage is the same, the sheet resistance decreases as the temperature rises and the current flowing through the infrared radiation layer increases, so the input power increases as the temperature rises, and the maximum temperature reached Can be high. In addition, when the power supply voltage is boosted by the booster circuit in order to obtain a voltage to be applied to the heat generating layer, it is possible to control the increase in the booster ratio of the booster circuit while increasing the maximum temperature reached. Can reduce power loss.

A fourteenth aspect of the invention is characterized in that, in the invention of any one of the first to thirteenth aspects, the infrared radiation element is selected from TaN and TiN.
According to this invention, since the oxidation resistance of the infrared radiation layer is high, the infrared radiation layer can be exposed and used in the air. In other words, it is not necessary to use in a vacuum or inert gas, the package structure is simplified, no window material for sealing is required, there is no attenuation of infrared by the window material, Use efficiency can be increased. Furthermore, since the sheet resistance of these materials can be adjusted by adjusting the nitrogen content, an infrared radiation layer having a small heat capacity is formed by adjusting the thickness dimension necessary to obtain a desired sheet resistance. As a result, high-speed response is possible.

  A fifteenth aspect of the present invention is the infrared radiation element according to any one of the first to fourteenth aspects, an infrared transmitter having a driving means for supplying power to the infrared radiation element to emit infrared rays, and an infrared ray having a predetermined wavelength only. A filter that transmits light, infrared light receiving means that receives the infrared light that has passed through the filter and outputs a light reception signal, and outputs a detection signal based on the light reception signal An infrared detector having detection means is provided.

According to the present invention, the infrared gas detector has the effect of any one of claims 1 to 14, and can achieve high accuracy and low power consumption.
According to a sixteenth aspect of the present invention, there is provided a mask process for applying an anodic oxidation mask to a peripheral edge of a predetermined area on one surface of a semiconductor substrate, a porous process for forming a porous layer by anodizing the predetermined area, and the porous An electropolishing step of forming a gas layer by electropolishing the region in the thickness direction of the semiconductor substrate facing the layer by anodic oxidation, and an infrared emitting layer forming step of forming an infrared emitting layer on the other side of the porous layer The thickness of the gas layer is set based on the frequency of the voltage applied to the infrared radiation layer, and the gas layer functions as a heat insulation layer when the infrared radiation layer is heated and functions as a heat dissipation layer when the temperature of the infrared radiation layer is lowered. It is characterized by that.

  According to this invention, the infrared radiation element manufactured by the present manufacturing method is such that the heat transferred from the infrared radiation layer to the holding layer when the temperature of the infrared radiation layer is raised is insulated by the gas layer. The temperature rise of the infrared radiation layer is not hindered by this, and the temperature rise time is shortened. When the temperature of the infrared radiation layer is lowered, the heat transferred from the infrared radiation layer to the holding layer is radiated to the semiconductor substrate through the gas layer. The temperature drop time of the infrared radiation layer is shortened by the gas layer acting as the heat dissipation layer. Therefore, the temperature of the infrared radiation layer is raised and lowered at a high speed, and the infrared radiation element can be driven at a high output and a high frequency. Further, the measurement time can be shortened and the power consumption can be reduced. In addition, by this production method, a low heat capacity and a high heat insulating property by a gas layer are provided by two-step anodic oxidation including formation of a porous layer by anodic oxidation and electrolytic polishing by anodic oxidation performed through the porous layer. A porous layer can be formed on the hollow.

  The invention of claim 17 is the invention of claim 16, further comprising a first doping step of doping impurities into a predetermined portion of the predetermined region before the masking step, and at the portion where the impurity doping is performed. Is formed of a support portion from the dope and a semiconductor substrate that is not made porous by the porosification step and is not polished in the thickness direction of the dope in the electropolishing step, and is not doped with impurities. The location is characterized in that a porous layer is formed by the porous step, and a gas layer is formed in a region of the semiconductor substrate facing the thickness direction of the porous layer in the electrolytic polishing step.

  According to the present invention, it is not necessary to separately perform an anodic oxidation mask on the holding layer by performing impurity doping on the portion of the surface on which the holding layer is to be formed, so that the infrared layer laminated on the holding layer. The step of the radiation layer and the non-uniform resistance portion can be eliminated, and an infrared radiation element capable of stable operation can be manufactured. Further, by forming the support portion, it is possible to prevent the support layer from adhering to the semiconductor substrate after the electrolytic polishing step and before the holding layer is dried.

  According to an eighteenth aspect of the present invention, in the invention of the sixteenth or seventeenth aspect, before the masking step, an impurity is applied to both the anodized mask and the predetermined region at the boundary between the anodized mask and the predetermined region on one surface of the semiconductor substrate. A second dope process for applying a dope is provided, and the portion subjected to the impurity doping is not made porous by the dope and the porosification process and is not polished in the thickness direction of the dope by the electrolytic polishing process. A porous silicon layer is formed by the porosification step in a portion where the reinforcing portion is formed from the remaining semiconductor substrate and is not doped with impurities, and is opposed to the thickness direction of the porous silicon layer in the electropolishing step. A gas layer is formed in a region of the semiconductor substrate to be processed.

  According to the present invention, when the gas layer is formed by the electropolishing process, the process proceeds isotropically. Therefore, when the impurity doped is not applied to the connection portion between the holding layer and the semiconductor substrate. The connection portion is removed, and the periphery of the holding layer is supported only by the anodic oxidation mask. However, the holding layer and the semiconductor are doped by doping impurities in the connection portion between the holding layer and the semiconductor substrate. Since the mask region by doping remains in the connection portion with the substrate, the strength of the connection portion can be increased, and the holding layer is prevented from being deformed and damaged due to the thermal expansion difference of the infrared radiation layer at the time of raising and lowering the temperature. be able to.

  The invention according to claim 19 is a sacrificial layer forming step of forming a sacrificial layer in a predetermined region of one surface of the semiconductor substrate, and a polysilicon layer forming step of forming an impurity-doped polysilicon layer on the surface of the sacrificial layer; A porous step of forming a porous layer by anodizing the polysilicon layer; and removing the sacrificial layer by etching the sacrificial layer through the porous layer, and one surface of the porous layer and the semiconductor substrate An etching step for forming a gas layer between the first surface and an infrared radiation layer forming step for forming an infrared radiation layer on the other surface of the porous layer, wherein the gas layer is applied to the infrared radiation layer. The thickness is set based on the frequency of the voltage, and it functions as a heat insulating layer when the infrared radiation layer is heated and as a heat radiation layer when the infrared radiation layer is cooled.

  According to this invention, the infrared radiation element manufactured by the present manufacturing method is such that the heat transferred from the infrared radiation layer to the holding layer when the temperature of the infrared radiation layer is raised is insulated by the gas layer. The temperature rise of the infrared radiation layer is not hindered by this, and the temperature rise time is shortened. When the temperature of the infrared radiation layer is lowered, the heat transferred from the infrared radiation layer to the holding layer is radiated to the semiconductor substrate through the gas layer. The temperature drop time of the infrared radiation layer is shortened by the gas layer acting as the heat dissipation layer. Therefore, the temperature of the infrared radiation layer is raised and lowered at a high speed, and the infrared radiation element can be driven at a high output and a high frequency. Further, the measurement time can be shortened and the power consumption can be reduced. Further, by providing a sacrificial layer to be removed by etching according to this manufacturing method, the polysilicon overlying the sacrificial layer is made into a porous layer by anodization, and the sacrificial layer is etched through the porous layer. The porous layer can be easily formed on the hollow.

  According to a twentieth aspect of the invention, in the invention of the nineteenth aspect, a predetermined region of the polysilicon layer facing the sacrificial layer in the thickness direction of the polysilicon layer is formed between the polysilicon layer forming step and the porous step. A portion where the impurity doping is performed is not anodized by the porosification step, and the portion where the doping is performed and the portion where the doping is performed are sacrificed. A part of the layer remains without being removed in the etching process to form a support part, and a portion not subjected to impurity doping forms a porous layer by a porous process, and the support process is performed by an etching process. The gas layer is formed by removing the sacrificial layer except for the portion to be a part.

  According to the present invention, by doping impurities into the polysilicon layer, a region that is not anodized in the polysilicon can be formed, and the sacrificial layer is etched after the polysilicon is anodized, so that the support portion can be easily formed simultaneously. be able to.

  As described above, the present invention provides an infrared radiation element capable of high output and high frequency drive and low power consumption, a manufacturing method thereof, and an infrared gas detector including the infrared radiation element. There is an effect that can be.

It is a cross-sectional schematic diagram of the infrared radiation element in Embodiment 1 of this invention. It is a top view of the infrared radiation element in the same as the above. It is explanatory drawing of the manufacturing method of the infrared radiation element in the same as the above. (A)-(d) shows the voltage waveform or temperature waveform of the infrared radiation element in the same as above, (a) is an applied voltage waveform, (b) is a temperature waveform when Expression 2 is satisfied, (c) Indicates a temperature waveform when the gas layer is not provided, and (d) indicates a temperature waveform when Equation 2 is not satisfied. It is a figure which shows the temperature characteristic in the holding layer of the infrared rays radiating element same as the above. In the infrared radiation element same as the above, a schematic view in the case where impurity doping is not applied to the periphery of the holding layer is shown. It is sectional drawing which shows the structure of the holding layer of the infrared rays radiating element same as the above. It is a top view of the infrared radiation element in Embodiment 2 of the present invention. It is explanatory drawing of the manufacturing method of the infrared rays radiating element in Embodiment 3 of this invention. The schematic of the infrared type gas detector in Embodiment 4 of this invention is shown. It is a front view of a light bulb type infrared radiation element provided with a coiled filament in a conventional example. It is a cross-sectional schematic diagram of a diaphragm type infrared radiation element in the same as above.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings.

(Embodiment 1)
The infrared radiating element A of the present embodiment will be described with reference to FIGS. 1 and 2, and then the manufacturing method of the infrared radiating element A will be described with reference to FIGS. In addition, let the direction orthogonal to the up-down left-right direction on the basis of the up-down-left-right in FIG.

  As shown in FIG. 1, the infrared radiation element A of the present embodiment includes a semiconductor substrate 1, a thin-film holding layer 2 formed on the upper surface of the semiconductor substrate 1, an upper surface of the semiconductor substrate 1, and a lower surface of the holding layer 2. A thin gas layer 3 composed of a space surrounded by the substrate, a support part 4 for connecting the upper surface of the semiconductor substrate 1 and the lower surface of the holding layer 2 in the gas layer 3 and supporting the holding layer 2, and the holding layer 2 And an infrared radiation layer 5 that emits infrared rays by heat generated by energization, and a pair of electrodes 6 for energization formed on the infrared radiation layer 5.

  As the semiconductor substrate 1, a substantially rectangular single crystal silicon substrate is used, and a predetermined region on the upper surface thereof is anodized in an aqueous hydrogen fluoride solution to form a porous silicon layer (porous) having a porosity of 70%. A substantially rectangular holding layer 2 made of a silicon layer is formed. The conductivity type of the silicon substrate used in the semiconductor substrate 1 may be either p-type or n-type. However, the p-type silicon substrate has a higher porosity when it is made porous by anodic oxidation. Since it tends to be easy, a p-type silicon substrate is preferably used as the semiconductor substrate 1. In addition, what is necessary is just to set suitably the current density at the time of anodizing a part of semiconductor substrate 1 according to the conductivity type and conductivity of the semiconductor substrate 1. The porous layer forming the holding layer 2 may be a porous polysilicon layer. Further, in order to provide an effect of suppressing electrical insulation and heat conduction in the front-rear and left-right directions, part or all of porous silicon or porous polysilicon may be oxidized or nitrided.

  The holding layer 2 is composed of a porous silicon layer, and its thermal conductivity and volumetric heat capacity decrease as the porosity increases.

  On the other hand, instead of making it porous by anodic oxidation, a semiconductor oxide film may be formed by thermal oxidation, and this semiconductor oxide film may be used as the holding layer 2. In the case where a semiconductor oxide film is used as the holding layer 2, if the holding layer 2 is formed by thermally oxidizing the semiconductor substrate 1 or if the holding layer 2 is formed by CVD using a material containing an oxide, the porous layer can be obtained. In comparison, the manufacturing process is simplified, and mass productivity can be improved. When the holding layer 2 is formed by CVD, it is possible to use an oxide with high thermal insulation such as alumina or a material containing this kind of oxide. Furthermore, a porous body of this type of material can be formed as the holding layer 2.

  The infrared radiation layer 5 is preferably selected from those made of TaN or TiN. These materials are excellent in heat resistance and oxidation resistance. Therefore, the infrared radiation layer 5 can be used in an air atmosphere, and the infrared radiation element A can be mounted on the substrate as a bare chip without being housed in a package. Further, even when housed in a package, it is not necessary to seal a window hole formed in the package in order to transmit infrared rays, and there is no attenuation of infrared rays by a window member attached to the window hole, so that infrared radiation efficiency is increased. be able to.

  Further, these materials have a physical property that the sheet resistance becomes a desired value to be described later in a thickness dimension (several tens of nm) suitable for forming the infrared radiation layer 5. Moreover, it can be controlled by the partial pressure of nitrogen gas during film formation of the sheet resistance. However, the material for forming the infrared radiation layer 5 can be other than TaN and TiN, and other metal nitrides or metal carbides may be used.

  The electrodes 6 are formed of a metal material (for example, aluminum) and are laminated on both the left and right ends of the infrared radiation layer 5, respectively, and a substantially sinusoidal voltage shown in FIG.

  When the input voltage is applied to the infrared radiation layer 5 via the pair of electrodes 6, the infrared radiation element A raises the temperature of the infrared radiation layer 5 to emit infrared light, and when the input voltage is turned off, the infrared radiation layer A emits infrared light. The radiation layer 5 cools down and stops emitting infrared rays. It is possible to increase the temperature during the voltage increase period and decrease the temperature during the voltage decrease period not only when the voltage applied to the infrared radiation layer 5 is interrupted but also when a voltage that changes sinusoidally is applied. is there. That is, the intensity of infrared light can be modulated according to the voltage applied to the electrode 6.

By the way, assuming that a sinusoidal voltage is applied to the electrode 6 of the infrared radiation element A having the above-described configuration, the thermal conductivity of the holding layer 2 is α _p [W / mK], and the volumetric heat capacity (specific heat capacity and density) of the holding layer 2. ) Is C _p [J / m ³ K], and the frequency at which the infrared radiation layer 5 can respond (twice the frequency of the applied voltage) is f [Hz], the thermal diffusion length μ of the holding layer 2 Is expressed by the following equation.
μ = (2α _p / ωC _p ) ^1/2 (Expression 1)
However, ω = 2πf.

When the heat which changes alternatingly from the infrared radiation layer 5 is given to the retention layer 2, the infrared rays radiated from the infrared radiation layer 5 toward the retention layer 2 are applied to the gas layer 3 on the lower surface of the retention layer 2. It is necessary to set the thickness dimension L _p of the holding layer 2 so as to come into contact. That is, it is desirable that the thickness dimension L _p of the holding layer 2 is set to a value that is at least smaller than the thermal diffusion length μ (L _p <μ).

Now, it is assumed that the holding layer 2 is formed of porous silicon, and the frequency f at which the infrared radiation layer 5 can respond, the volumetric heat capacity C _{p of} the holding layer 2 and the thermal conductivity α _p of the holding layer 2 are f = 10, respectively. When [kHz], C _p = 1.1 [W / mK], and thermal conductivity α _p = 1.05 × 10 ⁶ [J / m ³ K] are substituted into Equation 1 above, μ = 5.8 × 10 ⁻⁶ [m], and the thickness dimension L _p of the holding layer 2 needs to be smaller than 5.8 [μm].

Further, in order to increase the infrared radiation efficiency, it is desirable to satisfy the resonance condition represented by the following equation, where λ [m] is the desired infrared wavelength in vacuum and the refractive index of the holding layer 2 is n. .
n × L _p = m × λ / 2 (Formula 2)
However, m is a natural number.

The thickness dimension L _p of the holding layer 2 formed of porous silicon in the present embodiment is such that the desired infrared wavelength is 4 [μm], and if n = 1.35 and m = 1 in the above formula 2, L _p = 1.5 [μm]. That is, since L _p = 1.5 [μm] <5.8 [μm] = μ, the above formula 1 is also satisfied, and the conditions required in the present embodiment can be satisfied.

  That is, the holding layer 2 does not hinder the temperature rise of the infrared radiation layer 5 and can reduce the volumetric heat capacity of the infrared radiation layer 5 and the holding layer 2 as a whole. Therefore, the infrared radiation layer 5 can respond to the change of the applied voltage at high speed, and can increase the modulation frequency of the applied voltage.

  Further, by forming the holding layer 2 from a porous silicon layer, the volume heat capacity is reduced materially and the thermal response time is shortened compared to the case of forming it from a dense insulating material, and the temperature rising efficiency of the infrared radiation layer 5 is reduced. Can be further enhanced. Moreover, since the lower surface of the holding layer 2 is in contact with the gas layer 3 and gas generally has a lower thermal conductivity than the holding layer 2, the insulating layer 2 is thermally insulated from the holding layer 2 to the infrared radiation layer 5. This reduces the heat conduction path to the periphery of the infrared radiation layer and suppresses heat radiation to the periphery of the infrared radiation layer 5. Therefore, as shown by the curve b in FIG. 5, the temperature of the holding layer 2 supporting the infrared radiation layer 5 rises so that a large temperature difference does not occur in the depth direction when the infrared radiation layer 5 generates heat. become. 5 indicates a change in temperature in the depth direction of the holding layer 2 when the gas layer 3 is not provided.

Next, the gas layer 3 is formed between the upper surface of the semiconductor substrate 1 and the lower surface of the holding layer 2, and the thickness _Lg is desirably set under the following conditions. The applied voltage to the infrared radiation layer 5 is sinusoidal, the frequency of the applied voltage is f [Hz], the thermal conductivity of the gas layer 3 is α _g [W / mK], and the volumetric heat capacity of the gas layer 3 is C _g [J / M ³ K], the thickness dimension L _g of the gas layer 5 is set to a range represented by the following formula.
0. 05L _g '<L _g <3L _g ' (Formula 3)
However, L _g ′ = (2α _g / ωC _g ) ^1/2 and ω = 2πf.

For example, the voltage applied to the infrared radiation layer 5 is a sine wave having a frequency f = 10 [kHz], and the volumetric heat capacity C _{g of} the gas layer 3 and the thermal conductivity α _g of the gas layer 3 are respectively α _g = 0.0254. If [J / m ³ K] and C _g = 1.21 × 10 ³ [J / mK], from the above formula 3, 1.3 [μm] <L _g <77.5 [μm]. the thickness L _g of the gas layer 3, for example, by setting the 25 [μm], can satisfy the above equation 5. Desirably, the thickness is set so that the temperature amplitude ratio is maximized within this range.

Further, the gas layer. 3, since depending the temperature of the semiconductor substrate 1 in the thickness L _g between the temperature and the gas layer 3 of the holding layer 2 if constant with any of the functions of the heat dissipation and heat insulation Further, by adjusting the thickness dimension L _g of the gas layer 3 appropriately within the condition range of the above formula 3, the gas layer 3 is provided with heat insulation during the period when the applied voltage to the infrared radiation layer 5 is increased, and infrared radiation is emitted. During the period when the voltage applied to the layer 5 is lowered, the heat dissipation of the gas layer 3 can be provided.

  That is, it is possible to make the timing of using the heat insulation and heat dissipation of the gas layer 3 substantially coincide with the timing of increase / decrease of the voltage applied to the infrared radiation layer 5, and the voltage applied to the infrared radiation layer 5 is high frequency. Even when modulated by the above, it is possible to change the temperature of the infrared radiation layer 5 so as to be substantially synchronized with the frequency of the voltage. That is, it is possible to improve the responsiveness by providing the gas layer 3.

  Further, when the infrared radiation intensity is controlled by the drive voltage applied to the infrared radiation layer 5, if the power supplied to the infrared radiation layer 5 is the same, the drive voltage is reduced as the infrared radiation layer 5 has a lower sheet resistance. be able to. If the driving voltage is low, loss due to boosting can be reduced and the electric field strength in the infrared radiation element A can be reduced to reduce the possibility of breakage. Therefore, the sheet resistance is preferably small.

  Further, the infrared radiation layer 5 has a negative resistance temperature coefficient in which the sheet resistance decreases with increasing temperature. Therefore, even if the drive voltage is the same, the sheet resistance decreases as the temperature rises, and the current flowing through the infrared radiation layer 5 increases. That is, as the temperature rises, the input power increases, and the ultimate temperature can be increased.

Incidentally, the resistance temperature coefficient is set to −0.001 [° C. ⁻¹ ] using TaN for the infrared radiation layer 5, the maximum temperature reached during driving is set to 500 [° C.], and the sheet resistance at that temperature is set to 300 [° C. Ωsq], the sheet resistance at room temperature is 571 [Ωsq].

  As described above, when the infrared radiation layer 5 has a negative resistance temperature coefficient, when the power supply voltage is boosted by a booster circuit in order to obtain a voltage to be applied to the infrared radiation layer 5, the maximum temperature reached is reached. While increasing the voltage, the increase in the boost ratio of the booster circuit can be suppressed, and power loss in the booster circuit can be suppressed.

  Here, when the gas layer 3 is not provided, the heat insulation performance is insufficient and the heat radiation performance exceeds the heat insulation performance. Therefore, when an input voltage modulated at 10 kHz is applied, the temperature of the infrared radiation layer 5 is raised to a temperature at which a predetermined infrared intensity can be obtained at the temperature rise time T1, as shown in FIG. In other words, since the heat is dissipated in the temperature lowering time T2 and the low temperature state is maintained, the above effect cannot be obtained.

In addition, in the diaphragm type infrared radiation element 50 of the conventional example shown in FIG. 12, when the recess 52 is the gas layer 3, the thickness of the substrate 51 (525 μm) and the depth of the recess 52 are substantially equal. L _g becomes L _g = 525 μm, and the above formula 2 is not satisfied and the heat dissipation performance is insufficient. Therefore, when an input voltage modulated at 10 kHz is applied, the temperature of the infrared radiation layer 5 increases as the gas layer 3 acts as a heat insulating layer during the temperature rise time T1, as shown in FIG. 4 (d). However, since the heat dissipation performance is insufficient during the temperature lowering time T2, the temperature of the light emitting layer 54 increases each time the temperature rises and falls repeatedly, and becomes overheated and the above effect cannot be obtained.

  Next, the support part 4 is formed in a substantially truncated cone shape whose diameter is increased from the bottom to the top by single crystal silicon having higher mechanical strength than the porous layer, and the four support parts 4 are the gas layers 3. The upper surface of the semiconductor substrate 1 and the lower surface of the holding layer 2 are connected to each other and the holding layer 2 is supported. Therefore, it is possible to prevent the holding layer 2 from adhering to the semiconductor substrate 1 due to the difference in thermal expansion caused by the temperature rise and fall of the infrared radiation layer 5, and it is possible to prevent the infrared radiation layer 5 from being hindered in temperature rise and damaged due to deformation. In the present embodiment, the support portion 4 supports the lower surface of the holding layer 2, but the support portion 4 may support the holding layer 2 in a penetrating state.

  In particular, when the semiconductor substrate 1 is made of single crystal silicon and the support portion 4 is made of single crystal silicon with a part thereof remaining, the stress generated at the connection portion between the support portion 4 and the semiconductor substrate 1 becomes zero. The strength of the support part 4 is further increased and is more effective.

By the way, in the infrared radiation element A of the present embodiment, the peak wavelength of infrared radiation emitted from the infrared radiation layer 5 depends on the temperature of the infrared radiation layer 5, the peak wavelength is λ (μm), and the absolute temperature of the infrared radiation layer 5. Is T (K), the peak wavelength is
λ = 2898 / T (Formula 3)
Thus, the relationship between the absolute temperature T of the infrared radiation layer 5 and the peak wavelength λ of the infrared radiation emitted from the infrared radiation layer 5 satisfies the displacement side of Vienna. In short, the Joule heat generated per unit time in the infrared radiation layer 5 is changed by adjusting the amplitude and waveform of the voltage applied between the pair of electrodes 6 from an external power source (not shown) (that is, the infrared radiation layer 5 Temperature) and the peak wavelength λ of infrared rays emitted from the infrared emitting layer 5 can be changed.

  For example, it is possible to emit infrared rays having a peak wavelength λ of 3 μm to 4 μm by applying a voltage of about 100 V between the pair of electrodes 6, and by adjusting the voltage applied between the electrodes 6 appropriately, It is also possible to emit infrared rays having a wavelength λ of 4 μm or more.

  Further, in the configuration of the present embodiment, when the infrared radiation layer 5 is energized by the voltage mark applied to the electrode 6, infrared rays are emitted upward from the infrared radiation layer 5 as indicated by E1 in FIG. The holding layer 2 is heated by heat transfer from the infrared radiation layer 5 to the holding layer 2, and infrared rays are also emitted from the holding layer 2 due to a temperature rise of a part of the holding layer 2, as indicated by E 2 in FIG. Is done. Since the holding layer 2 supports the infrared radiation layer 5, heat is directly transferred from the infrared radiation layer 5, and it can be said that the infrared radiation layer 5 is used as a heat source to constitute a direct heat type infrared radiation source. .

  Here, the infrared radiation layer 5 has infrared transparency, and the infrared radiation radiated from the holding layer 2 in the direction toward the infrared radiation layer 5 passes through the infrared radiation layer 5 and is above the infrared radiation layer 5. Radiated. That is, from the infrared radiation element A, the infrared radiation E1 emitted upward from the infrared radiation layer 5 and the infrared radiation E2 transmitted from the holding layer 2 through the infrared radiation layer 5 and emitted above the infrared radiation layer 5 are combined. As a result, the infrared radiation efficiency with respect to the input power can be increased.

  The infrared radiation element A of the present embodiment configured as described above is a gas layer that acts as a heat insulation layer because the heat transmitted from the infrared radiation layer 5 to the holding layer 2 when the temperature of the infrared radiation layer 5 is increased is insulated by the gas layer 3. 3 does not inhibit the temperature rise of the infrared radiation layer 5 and the temperature rise time T1 is shortened. When the temperature is lowered, the heat transferred from the infrared radiation layer 5 to the holding layer 2 is radiated to the semiconductor substrate 1 through the gas layer 3. Therefore, the temperature lowering time T2 of the infrared radiation layer 5 can be shortened by the gas layer 3 serving as a heat dissipation layer. Therefore, the temperature change of the infrared radiation layer 5 shown in FIG. 4B rises and falls in synchronization with the waveform of the input voltage shown in FIG. 4A, and the infrared radiation element A emits high-power infrared light. High frequency driving can be achieved, and power consumption can be reduced.

  Hereinafter, the manufacturing method of the infrared radiation element A of this embodiment is demonstrated using Fig.3 (a)-(e). In addition, in the said infrared radiation element A, although the four support parts 4 are formed, in the description of this manufacturing method, it demonstrates as what the support part 4 is one.

First, as shown in FIG. 3A, for example, a doping is performed by applying P ⁺ impurity doping 8 surrounding a predetermined rectangular region on the upper surface of a substantially rectangular plate-shaped p-type semiconductor substrate 1 having a specific resistance of about 80 to 120 Ωcm. The process is performed, and a doping process is performed in which P ⁺ impurity doping 7 is applied to the approximate center in the left-right direction of the rectangular region. At that time, the impurity dope 7 is applied so that the diameter of the impurity dope 7 is larger than the diameter of the support portion 4, and further, has a thickness comparable to the thickness of the gas layer 3.

  Next, annealing treatment is performed to diffuse and activate the impurity dopes 7 and 8. Thereby, the region to which the impurity dopings 7 and 8 are applied becomes an n-type anodic oxidation mask. Thereafter, as shown in FIG. 3B, an oxidation treatment (pyro-oxidation) is performed on a region covering the impurity dope 8 formed in a rectangular frame shape on the upper surface of the semiconductor substrate 1 and a region outside the impurity dope 8. A mask process for applying the anodic oxidation mask 11 made of a silicon oxide film is performed. Then, after removing the silicon oxide film on the back surface of the semiconductor substrate 1, an aluminum electrode 9 for back contact is formed by sputtering.

And as shown in FIG.3 (c), the area | region except the part to which the impurity doping 7 and 8 was given in the said rectangular area | region is performed by performing the porosification process which anodizes the said rectangular area | region. The porous layer is formed to form a porous layer holding layer 2. Here, in the anodic oxidation treatment, a 30% hydrogen fluoride solution obtained by mixing a hydrogen fluoride aqueous solution and ethanol is used as the electrolytic solution, and only the surface to be anodized is brought into contact with the electrolytic solution. A platinum electrode (not shown) is arranged on the upper surface, set in a jig that can be energized from the lower surface, and a porous material having a thickness of 1 μm by flowing a current of a predetermined current density (for example, 100 mA / cm ² ) for a predetermined time. Form a quality layer.

  Further, the thickness of the holding layer 2 is formed based on the above formula 1, so that the infrared radiation layer 5 is heated at a high speed corresponding to the frequency of the applied voltage, and a large infrared intensity amplitude is obtained. be able to.

Subsequently, as shown in FIG. 3D, an electropolishing step of performing electropolishing of the region in the thickness direction of the semiconductor substrate 1 facing the holding layer 2 through the holding layer 2 made of the porous layer is performed. The gas layer 3 is formed. At this time, the substantially frustoconical support portion 4 is simultaneously formed by leaving the semiconductor substrate 1 below the portion where the impurity doping 7 has been applied. Here, in the electrolytic polishing treatment, a 15% hydrogen fluoride solution obtained by mixing an aqueous hydrogen fluoride solution and ethanol is used as the electrolytic solution, and only the surface to be anodized is brought into contact with the electrolytic solution. A gas having a thickness of 25 μm is arranged by placing a platinum electrode (not shown) on the upper surface, setting it on a jig that can be energized from the lower surface, and flowing a current of a predetermined current density (for example, 1000 mA / cm ² ) for a predetermined time. Layer 3 is formed.

  Here, the thickness of the gas layer 3 is formed on the basis of the above formula 2, so that the timing at which the gas layer 3 is switched from the heat insulation layer to the heat dissipation layer, and the voltage applied to the infrared radiation layer 5 is reduced from step-up to step-down. The switching timing can be made substantially coincident, and even when the voltage applied to the infrared radiation layer 5 is subjected to high frequency modulation, the infrared radiation layer 5 can be raised and lowered substantially in synchronization with the frequency of the voltage. In addition, a large infrared radiation amplitude can be obtained.

  In addition, since the process proceeds isotropically in the porosification process and the electropolishing process, when the impurity doping 8 is not performed, the periphery of the holding layer 2 is an anodizing mask 11 as shown in FIG. Therefore, the mechanical strength is small. However, in the present embodiment, since the impurity doping 8 is applied to the boundary between the holding layer 2 and the semiconductor substrate 1, the holding layer 2 has a periphery through the n-type silicon substrate formed by the impurity doping 8. It is connected to the semiconductor substrate 1 and has high mechanical strength.

  And as shown in FIG.3 (e), the infrared radiation layer formation process which laminates | stacks the infrared radiation layer 5 which consists of noble metal (Ir) which generate | occur | produces with electricity by about 100 nm in the area | region enclosed by the anodic oxidation mask 11 is performed, Thereafter, an electrode forming step is performed in which a pair of electrodes 6 are provided on both left and right ends of the infrared radiation layer 5. Here, the electrode 6 is provided by an evaporation method using a metal mask or the like. In this embodiment, the infrared radiation layer 5 is made of Ir, a noble metal, but the material is not limited to this, and may be a heat-resistant material that generates heat when energized, such as a heat-resistant metal, metal nitride, or metal carbide. The high emissivity is desirable.

  As described above, according to the manufacturing method of the infrared radiation element A shown in FIGS. 3A to 3E, by performing the two-step anodic oxidation of the porous step by anodic oxidation and the electrolytic polishing step by anodic oxidation, A porous layer (holding layer 2) having a low volumetric heat capacity and high heat insulation can be easily formed on the hollow.

  In addition, since the impurity doping 7 is applied to the portion where the support portion 4 is formed on the upper surface of the semiconductor substrate 1, it is not necessary to apply an anodic oxidation mask with a separate step to the portion where the support portion 4 is formed in the mask process. Infrared radiation element A capable of stable operation can be manufactured without causing step breakage or generation of non-uniform resistance in the infrared radiation layer 5 laminated on the upper surface.

  Furthermore, by forming the support portion 4, it is possible to prevent the holding layer 2 from adhering to the semiconductor substrate 1 in the drying process performed after the electropolishing process.

  In the present embodiment, a substantially sinusoidal voltage is applied as the input voltage. However, the input voltage is not limited to this and may be a substantially rectangular pulse voltage.

  In the present embodiment, as described above, a porous semiconductor obtained by making the semiconductor substrate 1 porous by anodic oxidation is used as the holding layer 2, and in addition to generating infrared rays by heat generation of the infrared emission layer 5, the infrared emission layer Infrared rays are generated by heating the holding layer 2 in 5 to increase the infrared radiation efficiency. However, by adopting the following structure as the holding layer 2, it is possible to further increase the infrared radiation efficiency. .

That is, as shown in FIG. 7, the holding layer 2 has a thickness of several nanometers within a macropore of several μm made of bulk silicon (not shown, but the surface of the bulk silicon is microscopically undulated). The nanopore is formed. This configuration is formed by adjusting the conductivity type, specific resistance, and anodic oxidation conditions (electrolyte composition, current density, processing time) of the semiconductor substrate 1 during anodic oxidation. For example, a p-type silicon substrate having a high resistance of about 100 Ωcm is used as the semiconductor substrate 1 and a hydrofluoric acid solution having a high concentration of hydrofluoric acid of about 25% is used as an anodic oxidation condition. The comparison is about 100 mA / cm ^2. It can be processed with a large current density.

  When the structure shown in FIG. 7 is adopted as the holding layer 2, when the holding layer 2 is heated by the heat from the infrared radiation layer 5, cavity radiation is generated by macropores, and the infrared emissivity can be further increased. In addition, since nanopores are formed in the macropores, only nano-sized fine irregularities are generated on the surface of the holding layer 2, and the surface state of the holding layer 2 has little influence on the infrared radiation layer 5. The infrared radiation layer 5 can be formed to a thickness of about several tens of nanometers.

  In order for the holding layer 2 to contribute to infrared radiation, the thickness dimension of the holding layer 2 needs to be set to 0.5 μm or more. This thickness dimension is set according to the relationship with the frequency of the voltage applied to the infrared radiation layer 5 using the formula 1.

(Embodiment 2)
The infrared radiation element B in the present embodiment is different from the infrared radiation element A of the first embodiment only in the arrangement of the infrared radiation layer 5. In addition, about the thing which has the function similar to the infrared radiation element A of Embodiment 1, the same code | symbol is attached | subjected and description is abbreviate | omitted.

  In the first embodiment, the infrared radiation layer 5 is laminated on the entire upper surface of the holding layer 2. However, in this embodiment, as shown in FIG. The two support portions 4 are respectively provided at predetermined intervals in the left-right direction on the lower surface side of the two holding layers 2 exposed between the three infrared radiation layers 5. Yes. In addition, in this embodiment, although the infrared radiation layer 5 is divided | segmented into three places, the division | segmentation number is not limited to this, Two places or four or more places shall be sufficient.

  As described above, since the infrared radiation layer 5 having higher thermal conductivity than the holding layer 2 does not directly contact the support portion 4, heat generated in the infrared radiation layer 5 is radiated to the semiconductor substrate 1 side through the support portion 4. That can be suppressed, and the luminous efficiency of the infrared radiation layer 5 can be increased.

  In addition, since the infrared radiation layer 5 and the support portion 4 are not in direct contact with each other, it is possible to suppress the occurrence of a large temperature gradient between the infrared radiation layer 5 and the support portion 4, and a large amount of heat caused by the temperature gradient. It can prevent that the infrared rays radiation layer 5 and the support part 4 are damaged by stress.

(Embodiment 3)
The manufacturing method of the infrared radiation element C in this embodiment is demonstrated using FIG. 9 (a)-(f). In addition, about the thing which has the function similar to the infrared radiation element A of Embodiment 1, the same code | symbol is attached | subjected and description is abbreviate | omitted. In addition, a direction orthogonal to the vertical and horizontal directions with reference to the vertical and horizontal directions in FIG.

  First, as shown in FIG. 9A, a sacrificial layer forming step is performed in which a sacrificial layer 13 having a thickness of about 5 μm is laminated by plasma CVD at a location where the gas layer 3 is formed on the upper surface side of the semiconductor substrate 1. .

  Next, as shown in FIG. 9B, an aluminum electrode 9 used for back contact at the time of anodizing is formed on the lower surface of the semiconductor substrate 1, and then a polysilicon layer having a thickness of 1 μm to which the impurity doping 7 is applied. A polysilicon layer forming step of covering the sacrificial layer 13 with the (holding layer) 2 is performed.

  Here, the thickness of the polysilicon layer 2 is formed based on the above formula 1, so that the infrared radiation layer 5 is heated at a high speed corresponding to the frequency of the applied voltage, and a large infrared intensity amplitude. Can be obtained.

Then, as shown in FIG. 9C, P ⁺ impurity doping 7 is ion-implanted into the region in the thickness direction of the polysilicon layer 2 substantially facing the sacrificial layer 13 with a predetermined spacing in the left-right direction. The dope process performed to two places is performed.

Subsequently, as shown in FIG. 9D, a porosification step is performed in which the polysilicon layer 2 is anodized to make it porous. Thereby, the portion where the impurity dope 7 is applied is not made porous, and the portion where the impurity dope 7 is not made is made porous. Here, in the anodic oxidation treatment, a 30% hydrogen fluoride solution obtained by mixing a hydrogen fluoride aqueous solution and ethanol is used as the electrolytic solution, and only the surface to be anodized is brought into contact with the electrolytic solution, so that the polysilicon layer 2 A platinum electrode (not shown) is disposed on the upper surface of the substrate, set in a jig that can be energized from the lower surface, and a porous layer is formed by flowing a current of a predetermined current density (for example, 100 mA / cm ² ) for a predetermined time. .

  Further, as shown in FIG. 9 (e), in the sacrificial layer 13, the portion facing the impurity dope 7 in the thickness direction of the polysilicon layer 2 remains without being removed by etching to form a support portion. The portion not facing the impurity dope 7 is removed by etching to perform an etching process for forming the gas layer 3. Here, an HF solution is used for the etching.

  Here, the thickness of the gas layer 3 is formed on the basis of the above formula 2, so that the timing at which the gas layer 3 is switched from the heat insulation layer to the heat dissipation layer, and the voltage applied to the infrared radiation layer 5 is reduced from step-up to step-down. The switching timing can be made substantially coincident, and even when the voltage applied to the infrared radiation layer 5 is subjected to high frequency modulation, the infrared radiation layer 5 can be raised and lowered substantially in synchronization with the frequency of the voltage. In addition, a large infrared radiation amplitude can be obtained.

  And as shown in FIG.9 (f), the infrared radiation layer formation process which laminates | stacks the infrared radiation layer 5 which consists of noble metal (Ir) which heat | fever-generates by electricity supply about 100 nm is performed on the upper surface of the holding layer 2, and the said An electrode forming step is performed in which a pair of electrodes 6 are provided on the left and right ends of the infrared radiation layer 5. Here, the electrode 6 is provided by an evaporation method using a metal mask or the like. In the present embodiment, the infrared radiation layer 5 is made of noble metal Ir, but the material is not limited to this, and may be a heat-resistant metal, metal nitride, metal carbide or the like.

  As described above, according to the method for manufacturing the infrared radiation element C shown in FIGS. 9A to 9F, after providing the sacrificial layer 13 removed by etching, the polysilicon layer 2 covering the sacrificial layer 13 is formed. By forming a porous layer by anodic oxidation and etching the sacrificial layer 13 through the porous layer, the gas layer 3 can be formed and the porous layer can be easily formed on the hollow.

  In addition, by applying the impurity doping 7 to the polysilicon layer 2 in advance, a region that is not anodized can be formed in the polysilicon layer 2, and when the sacrificial layer 13 is etched, a portion facing the impurity doping 7 in the thickness direction remains. By doing so, the gas layer 3 and the support part 4 can be easily formed simultaneously.

(Embodiment 4)
An embodiment of the present invention will be described with reference to FIG.

  As shown in FIG. 10, the infrared gas detector in the present embodiment includes an infrared transmitter 20 having an infrared radiation element A, an infrared detector 30 that receives infrared rays transmitted from the infrared transmitter 20, and infrared transmission. The light guide tube 40 that guides infrared rays transmitted from the vessel 20 to the infrared detector 30 is used, for example, for gas leak detection. In addition, in this embodiment, although the infrared radiation element A shown in Embodiment 1 is used, the infrared radiation element B shown in Embodiment 2 or the infrared radiation element C shown in Embodiment 3 may be used. .

  The infrared transmitter 20 includes an infrared radiation element A, a driving circuit (driving means) 21 that periodically supplies a single pulse power to the infrared radiation element A to emit infrared rays, and a hollow box type that houses the infrared radiation element A. The first casing 22 and a lens 23 that penetrates one surface of the first casing 22 and transmits infrared rays emitted from the infrared radiation element A and introduces them into the light guide tube 40. . The pulse power may be a single pulse or a plurality of continuous pulses.

  The infrared detector 30 has a hollow box-type second case 31 and a wavelength band that is penetrated through one surface of the second case 31 and is absorbed by a detection gas, which will be described later, in the infrared rays that are incident from the light guide tube 40. A filter 32 that transmits only the component, a pyroelectric infrared light receiving element (infrared light receiving means) 33 that is disposed in the second case 31 and receives infrared light transmitted through the filter 32, and light reception by the infrared light receiving element 33 It is comprised from the detection circuit (detection means) 34 which outputs a detection signal based on a result.

  The filter 32 includes two band pass filters 321 and 322 that transmit infrared rays having different wavelength bands, and are arranged in parallel. Here, the band-pass filters 321 and 322 determine the wavelength of infrared rays to be passed depending on the type of gas (detection gas) to be detected.

  The band-pass filters 321 and 322 are provided with infrared light receiving elements 331 and 332 so as to face each other. Note that the infrared light receiving elements 331 and 332 are referred to as infrared light receiving elements 33 when they are not distinguished.

  The light guide tube 40 is formed in a cylindrical shape in which a metal thin film such as gold is formed on the entire inner surface by sputtering, one end faces the lens 23 of the infrared transmitter 20, and the other end is a filter 32 of the infrared detector 30. It is provided in the atmosphere opposite to. The cylindrical wall of the light guide tube 40 is formed with a plurality of inflow / outflow holes 40a through which the detection target gas flows in or out, and when there is gas in the atmosphere, the inflow / outlet holes 40a are interposed. The gas also flows into the light guide tube 40.

  When infrared rays are sent from the infrared transmitter 20 into the light guide tube 40 in a state where gas flows into the light guide tube 40, the infrared rays are transmitted through the atmosphere containing the gas through the light guide tube 40. The detector 30 is reached.

  By the way, as detection gases, for example, carbon monoxide, carbon dioxide, and methane gas are targeted, and the wavelength band of infrared rays that are absorbed differs depending on the type of gas (for example, when detecting carbon dioxide, 4 .25 μm). Therefore, when the gas is present in the light guide tube 40, the infrared rays incident on the infrared detector 30 through the light guide tube 40 are compared with the case where no gas is present in the light guide tube 40. The wavelength band component absorbed by the gas decreases.

  Of the infrared rays that reach the infrared detector 30, only infrared rays that pass through the bandpass filters 321 and 322 are received by the infrared light receiving elements 331 and 332, respectively. Subsequently, the infrared light receiving elements 331 and 332 output a light reception signal to the detection circuit 34 based on the amount of received infrared light, and the detection circuit 34 detects gas based on the difference between the light reception signals input from the infrared light reception elements 331 and 332. The presence or absence of this is determined and a detection signal is output.

  And since the said infrared type gas detector is equipped with the infrared radiation element A which can drive high output and high frequency, it can achieve high precision and low power consumption.

  In the present embodiment, the filter 32 includes two bandpass filters 321, 322, but the number of bandpass filters may be three or more.

DESCRIPTION OF SYMBOLS 1 Semiconductor substrate 2 Holding layer 3 Gas layer 4 Support part 5 Infrared radiation layer 6 Electrode 21 Drive circuit (drive means)
32 Filter 33 Infrared light receiving element (infrared light receiving means)
34 Detection circuit (detection means)
A to C Infrared radiation element

Claims (20)

A semiconductor substrate;
A thin-film holding layer formed on one surface of the semiconductor substrate;
A gas layer composed of a space surrounded by one surface of the semiconductor substrate and one surface of the holding layer;
An infrared radiation layer that is laminated on the other surface of the holding layer and emits infrared rays by heat generated by electrical input;
The gas layer has a thickness set based on the frequency of the voltage applied to the infrared radiation layer, and functions as a heat insulating layer when the infrared radiation layer is heated, and as a heat dissipation layer when the infrared radiation layer is cooled. Infrared emitting element.   The infrared radiation element according to claim 1, wherein the gas layer is provided with a support portion that connects the semiconductor substrate and the holding layer and supports the holding layer.   The infrared radiation element according to claim 2, wherein the support portion is made of single crystal silicon.   The infrared radiation layer is laminated | stacked in multiple places on the other surface of the said retention layer, and the support part is provided in the one surface side of the retention layer exposed between infrared radiation layers. Infrared radiation element.   The infrared radiation element according to claim 1, wherein the holding layer is made of a porous layer.   6. The infrared radiation element according to claim 5, wherein the porous layer is made of porous silicon or porous polysilicon.   The infrared radiation element according to claim 1, wherein a peripheral edge of the holding layer is fixed to a semiconductor substrate.   The infrared radiation element according to claim 7, wherein a portion where the semiconductor substrate and the holding layer are joined includes a reinforcing portion that reinforces the joining between the holding layer and the semiconductor substrate. The holding layer has a thermal conductivity smaller than that of the semiconductor substrate, and at least one of a temperature rise due to heat transfer from the infrared radiation layer accompanying energization of the infrared radiation layer and reflection of infrared rays incident from the infrared radiation layer Radiates infrared rays in the direction toward the infrared radiation layer,
The infrared radiation element according to any one of claims 1 to 8, wherein the infrared radiation layer has a function of passing infrared radiation radiated from the holding layer.   The infrared radiation element according to any one of claims 1 to 9, wherein a thickness dimension of the holding layer is set to a dimension in which an optical path length with respect to an infrared ray having a target wavelength is a natural number multiple of a half wavelength of the infrared ray. .   11. The infrared radiation according to claim 1, wherein the holding layer has a structure in which macropores that emit infrared rays by cavity emission during heating are formed in a bulk semiconductor, and nanopores are formed in the macropores. element.   The infrared radiation element according to claim 1, wherein the holding layer is formed of an electrical insulating film containing a semiconductor oxide.   The infrared radiation element according to any one of claims 1 to 12, wherein the infrared radiation element is formed of a material having a negative resistance temperature coefficient.   The infrared radiation element according to claim 1, wherein the infrared radiation element is selected from TaN and TiN. An infrared transmitter having an infrared radiation element according to any one of claims 1 to 14, and a driving unit that supplies electric power to the infrared radiation element to emit infrared rays;
A filter that transmits only infrared light having a predetermined wavelength, an infrared light receiving means that has the highest sensitivity to infrared light having the wavelength, receives infrared light that has passed through the filter, and outputs a light reception signal; and An infrared gas detector comprising: an infrared detector having detection means for outputting a detection signal based thereon. A mask process for applying an anodizing mask to the periphery of a predetermined region on one surface of the semiconductor substrate;
A porous step for forming a porous layer by anodizing the predetermined region;
An electropolishing step of forming a gas layer by electropolishing the region in the thickness direction of the semiconductor substrate facing the porous layer by anodic oxidation;
An infrared radiation layer forming step of forming an infrared radiation layer on the other surface side of the porous layer,
The gas layer has a thickness set based on the frequency of the voltage applied to the infrared radiation layer, and functions as a heat insulating layer when the infrared radiation layer is heated, and as a heat dissipation layer when the infrared radiation layer is cooled. A method for manufacturing an infrared radiation element.   Before the masking step, a first doping step is performed in which a predetermined portion of the predetermined region is doped with an impurity, and the portion where the impurity doping is performed is not made porous by the porosification step and the electrolysis In the polishing step, a support portion is formed from the semiconductor substrate remaining without being polished in the thickness direction of the dope, and a porous layer is formed in the porosification step at a portion not subjected to impurity doping, and the electrolytic polishing 17. The method of manufacturing an infrared radiation element according to claim 16, wherein a gas layer is formed in a region of the semiconductor substrate facing the thickness direction of the porous layer in the process.   Prior to the masking step, a second doping step is performed in which impurity doping is applied to both the anodization mask and the predetermined region at the boundary between the anodization mask and the predetermined region on one surface of the semiconductor substrate. A reinforcing portion is formed in the formed portion from the dope and the remaining semiconductor substrate that is not made porous by the porosification step and is not polished in the thickness direction of the dope by the electropolishing step, and is doped with impurities. A porous silicon layer is formed in the porous region by the porous step, and a gas layer is formed in a region of the semiconductor substrate facing the thickness direction of the porous silicon layer in the electrolytic polishing step. The method for manufacturing an infrared radiation element according to claim 16 or 17. A sacrificial layer forming step of forming a sacrificial layer in a predetermined region on one surface of the semiconductor substrate;
Forming a polysilicon layer doped with impurities on the surface of the sacrificial layer; and
A porosification step of forming a porous layer by anodizing the polysilicon layer;
An etching step of removing the sacrificial layer by etching the sacrificial layer through the porous layer and forming a gas layer between one surface of the porous layer and one surface of the semiconductor substrate;
An infrared radiation layer forming step of forming an infrared radiation layer on the other surface of the porous layer,
The gas layer has a thickness set based on the frequency of the voltage applied to the infrared radiation layer, and functions as a heat insulating layer when the infrared radiation layer is heated, and as a heat dissipation layer when the infrared radiation layer is cooled. A method for manufacturing an infrared radiation element. A doping step of doping impurities in a predetermined position in a region facing the sacrificial layer of the polysilicon layer in the thickness direction of the polysilicon layer between the polysilicon layer forming step and the porous step; The doped part is not anodized by the porous process, and the part where the dope is applied and the part of the sacrificial layer facing the doped part remain without being removed by the etching process. By forming the support part, the part where the impurity is not doped is formed by forming the porous layer by the porous process, and removing the sacrificial layer except the part that becomes the support part by the etching process. The method for manufacturing an infrared radiation element according to claim 19, wherein a gas layer is formed.

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