JPS61154086A - Semiconductor temperature sensor - Google Patents

Abstract

PURPOSE:To obtain a semiconductor temperature sensor having high sensivity by coating the surface of a compound semiconductor substrate, to which a field-effect transistor is formed, with an insulating material film having a thermal expansion coefficient different from a compound semiconductor in the substrate. CONSTITUTION:The title sensor detects a temperature in such a manner that a FET forming region on a compound semiconductor substrate consisting of GaAs, etc. is coated with a material having a thermal expansion coefficient different from the compound semiconductor substrate, stress depending upon a temperature is generated and the change of carrier concentration due to piezoelectric polarization generated as the result of the generation of stress is utilized. That is, a FET in which currents vary is shaped onto a GaAs(100) face as an n channel FET, the direction of channel length, the direction of drain currents, is formed conformed to the direction of the arrow, and approximately the whole region and the peripheral region of a region in which the FET 3 is shaped is coated with an SiO2 film 2 having thickness of approximately 1mum. Since the film 2 generates stressin the GaAs substrate 1 by utilizing a difference between thermal expansion coefficients, it is desirable that thickness thereof is increased comparatively.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention relates to a semiconductor device used for temperature detection, and in particular to thermal distortion of a field effect transistor (hereinafter abbreviated as PET) formed in a compound semiconductor. The present invention relates to a temperature sensor that utilizes characteristic changes due to

Although there are various types of sensors that detect temperature, semiconductor temperature sensors that utilize the thermal properties of semiconductor materials are widely used for equipment control because they output temperature information as electrical signals.

[Prior art and problems to be solved by the invention] Conventional semiconductor temperature sensors detect temperature through changes in the resistance value of resistance elements formed on semiconductor substrates and changes in the saturation current of transistor elements. In principle, many of them utilize the concentration of thermally excited carriers within a semiconductor substrate and the temperature dependence of their mobility.

In order to improve detection sensitivity, improvements have been made to the shape of the element and the selection of materials, but there are limits to the degree of improvement.

[Means for solving problems]

The above-mentioned problems are solved by the device of the present invention as set forth in the claims, but the present invention can be summarized by the embodiments described below. This device covers the formation region with a material having a coefficient of thermal expansion different from that of the compound semiconductor substrate to generate temperature-dependent stress, and detects temperature by utilizing the resulting change in carrier concentration due to piezoelectric polarization.

[Effect]

Compound semiconductor crystals generate piezoelectric polarization when subjected to elastic deformation due to external force. For this reason, the carrier concentration within the compound semiconductor substrate appears to be epithelialized, and the characteristics of the FET are affected by external forces applied to the substrate.The present invention utilizes this phenomenon.
It utilizes piezoelectric polarization generated through elastic deformation of the substrate surface due to residual stress in an insulating film deposited on the substrate by chemical vapor deposition (CVD) or the like.

The residual stress in this insulating film depends on its deposition conditions and temperature, and is expressed by the following equation.

σ = σ50 (α, -αr) A (T-Ta) where,
σ is the stress value at the temperature T, σ is the true stress value at the stacked state B (temperature T4), α1. α.

are the thermal expansion coefficients of the substrate and the insulating film, respectively, and A is a constant.

Generally, when stress values are compared when deposited near room temperature and at 300 to 500°C, the stress values are often larger at higher temperatures.

Piezoelectric polarization and its effect on FET characteristics depend on the crystal orientation of the compound semiconductor substrate. For example, if an FET is formed on a GaAs (100)-plane substrate with the drain current flowing in the (011) direction, and it is covered with an insulating film (for example, Sing) that has residual stress that applies compressive stress to the substrate. , positive charges are induced in the channel region of the FET. Therefore, when the FET is made into an n-channel, the drain current decreases, and when the FET is made into a p-channel, the drain current increases. Furthermore, if the drain current is in the (OIT) direction, or if an insulating film (e.g. SiN 11) with residual stress that applies tensile stress to the substrate is used, the charge induced in the channel region will be negative. .

Incidentally, the carrier concentration due to thermal excitation increases at high temperatures, and the mobility tends to decrease slightly, resulting in an increase in the current value of the transistor element. Therefore, if an FET is formed in the direction in which the majority carriers in the channel region increase due to piezoelectric polarization, the carrier concentration due to piezoelectric polarization increases and decreases in the same direction as the carrier concentration due to temperature changes. The range of change in output becomes larger relative to the range of change in . That is, the sensitivity of the temperature sensor can be improved.

〔Example〕

- are a plan view and a sectional view showing the structure of an embodiment of the present invention.

In this embodiment, F, which is an element that generates a current change,
The ET has the structure shown in the top view (a) and its x-x' cross-sectional view (bl), and the FET is made of GaAs.
It is formed as an n-channel FET on the (10G) plane, and the channel length direction, that is, the drain current direction is shown in Figure (a).
As shown in (01 block) direction, the F
Approximately the entire area where ET3 is formed and the surrounding area are 1
It is covered with a Sing film 2 having a thickness of about μm. Since this film generates a substrate force on the GaAs substrate by utilizing the difference in thermal expansion coefficient, it is desirable to make the film relatively thick.The reason why such a structure is effective for temperature detection will be described below. .

As mentioned above, when a FET formed so that the drain current flows in the (OIT) direction is coated with a SiO film, negative charges are induced in the channel by piezoelectric polarization, and the temperature change is caused by an increase or decrease in carriers due to thermal excitation. The same tendency occurs, and therefore, the temperature change in current value becomes larger compared to a conventional type that does not utilize piezoelectric polarization, and a highly sensitive temperature sensor is realized.

GaAs used as a temperature sensitive element in the present invention
The FET 3 is an FET (hereinafter abbreviated as MESFET) having a Schottky barrier gate with a gate length of approximately 11 m, and is manufactured using tungsten silicide (WSi), a highly heat-resistant alloy, after forming the channel region 4 by ion implantation and annealing. ) etc. to form the gate electrode 5, and then ion implantation and annealing again to form the source and drain N regions 6.
．． 7 and forming the source and drain electrodes 8.9 by depositing and alloying the AuGe/Au layers can be applied without any disadvantage.

What is different from normal FETs is the insulating coating of SiO□
The method for forming the film 2 is that after forming the FET, the temperature of the substrate is raised to about 500° C., and the film is deposited to a thickness of about 1 μm by CVD. As mentioned above, this is to effectively generate current changes due to thermal strain, so from this point of view it is better to raise the formation temperature as high as possible and generate larger stress. but,
If the formation temperature is too high, disadvantages such as destruction of sirotchivalry due to GaAs substrate/gate electrode interface reaction and abnormal increase of impurities in the channel region due to re-diffusion will occur. 5
The value of 00° C. is close to the upper temperature limit at which such disadvantages do not occur in the high temperature state for about 10 minutes required to deposit 111 m of S i Ot.

In this example, an n-channel MESFET is formed on a GaAs (100)-plane substrate, but this can be made into a p-channel with the drain current direction parallel to the (011) direction, or SiN* can be used as an insulating film. It is possible to obtain the same effect with any method, and the manufacturing method is not limited to the Selfaline type.
It is also possible to form a temperature sensor with a similar effect using a substrate such as a surface.

〔Effect of the invention〕

As explained above, the present invention realizes a semiconductor temperature sensor with higher sensitivity than conventional devices.

[Brief explanation of the drawing]

FIG. 1 is a plan view and a cross-sectional view showing the structure of a sensor according to the present invention, in which l indicates a GaAs substrate 2 is a thick SiOx film 3 and a Schitt Kibarya FET.

Claims (3)

[Claims] (1) A semiconductor temperature sensor characterized in that a compound semiconductor substrate surface on which a field effect transistor is formed is covered with an insulating material film having a coefficient of thermal expansion different from that of the compound semiconductor. (2) The structure is formed so that stress generated in the compound semiconductor substrate due to residual stress in the insulating film material induces piezoelectric polarization that increases the majority carrier concentration in the channel region of the field effect transistor. A semiconductor temperature sensor according to claim 1, characterized in that: (3) The semiconductor temperature sensor according to claim 2, wherein the compound semiconductor is gallium arsenide.