JPH04356979A - Infrared ray sensor - Google Patents

Abstract

PURPOSE:To provide a thermistor type thermal conversion infrared ray sensor which has high sensitivity, a low resistance value and low noise, and which is easily realized. CONSTITUTION:An infrared ray sensor 1 having a thin film 6 which has thermistor characteristics for detecting an infrared ray according to a temperature rise of the film 6, wherein the film 6 is a thin amorphous semiconductor film and electrodes 5, 7 are laminated to be formed on the front and rear surfaces of the film.

Description

[Detailed description of the invention]

0001

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a thermistor type heat conversion type infrared sensor.

0002

[Prior technology] Thermistor type heat conversion type infrared sensor (
As an infrared detection element), the inventors used a polycrystalline silicon thin film with an average grain size of 0.01 to 1.0 μm and a thickness of 0.1 to 5.0 μm as a thin film having thermistor characteristics, and a plurality of An infrared sensor with electrodes formed was developed and investigated. This infrared sensor has a smaller heat capacity, higher sensitivity, and faster response speed than conventional ceramic sensors.
Furthermore, it has been found that it has many features, such as being able to be integrated with an IC and being formed on the same substrate as a signal processing circuit.

0003

[Problems to be Solved by the Invention] However, as a result of study, it has been found that the above-mentioned infrared sensor has the following points to be improved. One is, as shown in Figure 3.
Only a comb-shaped electrode structure in which all the electrodes 31 are provided evenly on the surface of the polycrystalline silicon thin film 30 can be adopted. Since the temperature during formation of the polycrystalline silicon thin film 30 is 700° C. or higher, electrodes cannot be provided in advance before the polycrystalline silicon thin film is formed, so the polycrystalline silicon thin film is first formed on the substrate 32. After that, all the electrodes 31 have to be arranged on the surface of the thin film 30. In the case of a comb-shaped electrode structure in which all the electrodes 31 are aligned on the same side, there are the following problems.

The first problem is that if high sensitivity is desired, it is virtually impossible to bring the resistance value of the polycrystalline silicon thin film resistor into an appropriate range. Infrared rays are detected by the rise in temperature of the thin film due to infrared absorption, and in order to achieve high sensitivity, the resistance value change (usually expressed as the "B constant") with respect to temperature changes of the polycrystalline silicon thin film is large. is necessary. In the case of polycrystalline silicon thin films, the B constant corresponds to the activation energy (hereinafter referred to as "Ea"), and as can be seen from Figure 5, in order to obtain a large Ea, it is necessary to use an intrinsic semiconductor to which no impurities are added. good. However, as shown in FIG. 4, since the dark conductivity σRT of an intrinsic semiconductor is extremely small, the resistance value of the thin film resistor becomes extremely large. The resistance value required by an infrared sensor is approximately 1 MΩ.

[0005] In order to achieve 1 MΩ with the above-mentioned intrinsic semiconductor with extremely low dark conductivity σRT, it is necessary to: 1) make the thin film extremely thick (10 μm or more), 2) make the gap between the electrodes very narrow (~ 1μm) ■It will be necessary to take measures such as making the width of the resistor much wider (several mm or more). However, considering constraints such as thin film quality, microfabrication capability, and element size, the above three measures are hardly realistic. This is because even if a polycrystalline silicon thin film with a thickness of 1 μm and a width of 16 mm has an interelectrode gap of 20 μm, which can be said to be within a realistically possible range at present, the resistance value will be 40 M or more.

The second problem is that of noise. When obtaining high sensitivity, it is important to have a high S/N ratio as well as a high B constant. In other words, the noise of the polycrystalline silicon thin film resistor must be kept low. Normally, noise includes thermal noise and excessive noise, but in this case, the excess noise accounts for a larger proportion than the thermal noise, and the excess noise is the main problem. Excessive noise in semiconductors such as polycrystalline silicon is
NOISE(ALDERT VAN DER ZIEL
), under certain conditions it is inversely proportional to the volume of the resistor. In the MSD and comb-shaped electrode structure, as shown in Figure 3, the electrode forming part of the diagonal lattice does not fit into the above volume and is considered to be only between the parts of the diagonal lattice, so there is a large loss in terms of excessive noise reduction. This makes it difficult to achieve a low noise level.

SUMMARY OF THE INVENTION In view of the above circumstances, it is an object of the present invention to provide a thermistor type thermal conversion type infrared sensor which is highly sensitive, has a low resistance value, has low noise, and is easy to implement.

[0008]

[Means for Solving the Problems] In order to solve the above problems, an infrared sensor according to the present invention includes a thin film having thermistor characteristics, and detects infrared rays by increasing the temperature of the thin film due to infrared absorption. The thin film is an amorphous semiconductor thin film, and electrodes are laminated on each of its front and back surfaces.

In the case of the infrared sensor (infrared element) of the present invention, a back side electrode is usually formed on an insulating film, then an amorphous semiconductor thin film is laminated, then a front side electrode is formed, and finally the back side electrode is formed on the insulating film. It has a laminated structure in which an infrared absorbing film is laminated on top. An appropriate example of the insulating film is an insulating film spanning the trenched space of the silicon substrate. In this case, the sensor portion on the insulating film is thermally and electrically insulated from the silicon substrate by the insulating film. Since the contact area between the silicon substrate and the insulating film is small, there is sufficient heat isolation between the silicon substrate and the insulating film, and in other parts, the space plays the role of heat isolation. Therefore, the infrared absorbed heat is effectively used to raise the temperature of the sensor section without being dissipated to the outside.

[0010] The insulating film is preferably a multilayer film in which silicon oxide films and silicon nitride films are laminated. This is because warpage can be reduced by appropriately combining thin films with tensile and compressive properties. However, it goes without saying that the insulating film may be a single silicon oxide film or a single silicon nitride film. The back side electrode provided on the surface of the insulating film is made of Al
Although a metal thin film electrode such as NiCr or Cr may be used, a NiCr metal thin film electrode with good thermal insulation properties is preferable.

[0011] As the amorphous semiconductor thin film having thermistor characteristics, an amorphous silicon-based material, specifically,
Suitable examples include amorphous silicon and amorphous silicon alloys such as SiC and SiN. The surface-side electrode provided on the amorphous semiconductor thin film is also a metal thin film electrode made of Al, Cr, NiCr, or the like.

For example, gold black (
Gold and black) are used. Note that if another film, for example, the electrode thin film itself has an infrared absorbing film function, there is no need to provide an infrared absorbing film.

[0013]

[Operation] In the infrared sensor of the present invention, since the thin film having thermistor characteristics is an amorphous semiconductor thin film, a sandwich type electrode structure can be adopted in which electrodes are formed on each of the front and back surfaces of the thin film. Since an amorphous semiconductor thin film can be formed at a low temperature of about 300° C., even if it is formed on a metal thin film for an electrode, it will not be contaminated by metal diffusion from below. The sandwich type electrode structure is a structure that can easily achieve a low resistance value, and as a result, it is not only possible to achieve both high sensitivity and low resistance value within a practical range that is easy to realize, but also to completely eliminate the thin film between the electrodes. Since it is a resistor, there is almost no loss and excess noise is reduced.

[0014] Thus, the infrared sensor of the present invention has
It is highly sensitive and has low noise, making it possible to detect weak outside lines.Moreover, its low resistance makes it compatible with signal processing circuits, making it easy to use and easy to implement, making it extremely practical. Highly sexual.

[0015]

[Example] Hereinafter, an example of an infrared sensor of the present invention will be described.
This will be explained in detail with reference to the drawings. Of course, the present invention is not limited to the following embodiments. FIG. 1 shows a cross section of a main part of an infrared sensor with a sandwich-type electrode structure according to an example, and FIG. (not shown).

In the infrared sensor 1 of the embodiment, a thin sensor section is provided on an insulating film 3 that spans a digging space 2a of a silicon substrate 2. The dug space 2a of the silicon substrate 2 is formed by etching from the back surface toward the front surface using an HF-HNO3 or KOH-based etching solution. The insulating film 3 has a five-layer structure in which silicon oxide films and silicon nitride films are alternately laminated, and plays the role of thermal insulation and electrical insulation. In addition, in order to further improve thermal insulation properties of the insulating film 3,
The slit 3a is provided to reduce the contact area with the silicon substrate side.

On the other hand, the sensor section is formed by laminating a back side thin film electrode 5, an amorphous semiconductor thin film 6, a front side thin film electrode 7, and an infrared absorbing film (thin film) 8 in this order, and the insulating film 3 absorbs the necessary heat. Insulation and electrical insulation are ensured. The infrared rays incident on the sensor section are converted into heat in the absorption film 8 and then increase the temperature of the amorphous semiconductor thin film 6 without being dissipated. The sensor of the present invention can be used, for example, to detect infrared emitters (eg, humans).

The configuration of the embodiment has a dark conductivity of 10-9 (Ω/c
It was confirmed that an electrode with an area of 1 mm 2 was formed on a 1 μm thick non-doped thin film 6 with a B constant of 8000 and a resistance value of about 1 MΩ. Furthermore, by actually injecting infrared rays, it was confirmed that the noise level was low and had a good S/N ratio.

[0019]

[Effects of the Invention] As described above, the infrared sensor of the present invention has a configuration in which electrodes are formed on each of the front and back surfaces of an amorphous semiconductor thin film having thermistor characteristics, and is easy to realize and practical. It is capable of detecting weak infrared rays with high sensitivity and low noise within a certain range, and has low resistance and good compatibility with signal processing circuits, making it easy to use and extremely practical.

[Brief explanation of drawings]

FIG. 1 is a partial cross-sectional view showing the main part configuration of an infrared sensor according to an embodiment.

FIG. 2 is a partially cutaway perspective view showing the main structure of the infrared sensor according to the embodiment.

FIG. 3 is a sectional view showing the main part configuration of a conventional infrared sensor.

FIG. 4 is a graph showing the doping level dependence of dark conductivity at room temperature in a semiconductor.

FIG. 5 is a graph showing the doping level dependence of activation energy of dark conductivity in a semiconductor.

[Explanation of symbols]

1 Infrared sensor 2 Silicon substrate 3 Insulating film 5　Back side thin film electrode 6 Amorphous semiconductor thin film 7 Surface side thin film electrode 8 Infrared absorption film

Claims (2)

[Claims] [Claim 1] A thin film having thermistor characteristics,
An infrared sensor that detects infrared rays by increasing the temperature of the thin film due to infrared absorption, wherein the thin film is an amorphous semiconductor thin film, and electrodes are laminated on each of the front and back surfaces of the infrared sensor. sensor. 2. The infrared sensor according to claim 1, wherein the amorphous semiconductor thin film is formed of an amorphous silicon-based material.