JPH0227826B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Application Field] The present invention focuses on three characteristics of an amorphous semiconductor thin film with high conductivity, namely, a p ⁺ type thin film,
Concerning ^a thin film p + -n ⁺ junction type amorphous semiconductor thermocouple element constructed by focusing on the large thermoelectric power of the n + type thin film, the ohmic properties of the p ⁺ -n ⁺ junction, the ease of thin film formation, and the microfabricability ^. . To explain in more detail, the p ⁺ type and n ⁺ type are different from the conventional p type, n
with higher conductivity than amorphous semiconductors,
In other words, the inventor found that σ is at least 1 (Ω cm) ^-1 or more,
The present invention relates to a p ⁺ -n ⁺ junction type amorphous semiconductor thermocouple element made of this amorphous semiconductor. In particular, the present invention relates to power detection elements ranging from direct current to light waves constructed by applying this thermocouple element.

[Conventional technology]

Traditionally, a bolometer has been used as a detection element to measure power (especially high-frequency power), but recently, thin film thermocouple elements such as Bi-Sb and Si
- A semiconductor-thin film thermocouple element represented by Ta ₂ N is used. A method that uses a bolometer such as a thermistor or barrette as a detection element indirectly measures the incident power from the change in resistance value that occurs when high-frequency energy is absorbed, and the resistance value is sensitive to changes in the surrounding temperature. As a result, the zero point fluctuates, and a circuit to compensate for this zero point drift is required. Furthermore, in the case of a thermistor, the input standing wave ratio increases as the frequency increases, and in the case of a barrette, there are drawbacks such as being susceptible to overcurrent. In the method using a thin film thermocouple element or a semiconductor-thin film thermocouple element as a detection element, the thin-film thermocouple element or semiconductor-thin film thermocouple element absorbs incident high-frequency power and generates a direct current thermal wave proportional to the incident power. It is measured by converting it into electric power.

This method has a small zero point drift due to changes in ambient temperature, but it is difficult to measure small amounts of power below 1 μW. In particular, in the case of thin-film thermocouple elements such as Bi-Sb, the thermoelectromotive force per pair is as small as 120 μV/℃ at most, and the melting point of the metal is low. When a vapor-deposited film is formed on the substrate, the adhesion to the substrate becomes weak. Moreover, since the film quality is damaged by water or organic solvents, microfabrication techniques such as photo-etching cannot be used, resulting in a large element shape, which limits the detectable frequency range and reduces the response speed. There are drawbacks such as the fact that it takes several seconds to complete. On the other hand, in a semiconductor-thin film thermocouple element represented by Si-Ta ₂ N, the thermal conductivity of the Si supporting substrate is approximately 1.45 W/cm. ℃ and large. Therefore, in order to increase the detection sensitivity of thermocouple elements, it is necessary to make the Si substrate thinner.
It is 5 μm. Since a selective etching technique is normally used to thin a part of a chip-shaped Si substrate, it is necessary to form an etching stopper diffusion layer on the Si substrate in advance.

In addition, a method of using a semiconductor thin film with high thermoelectric power instead of a metal thin film has been considered, but the film lacks stability and cannot be microfabricated, and silicon thin films require a substrate deposition temperature of 700°C or higher. Since it is necessary, there is little practical merit.

As described above, the semiconductor-thin film thermocouple element has a complicated structure and is also difficult to manufacture.

On the other hand, with the progress of thin film formation technology, various methods of constructing thermocouples using semiconductor thin films have been studied (for example, Japanese Patent Laid-Open No. 53-143180 and Japanese Patent Laid-Open No. 57-7172). It is true that when a semiconductor thin film is formed using the vacuum evaporation method, sputtering method, or plasma CVD method, the crystallinity is lost and it becomes amorphous, resulting in a thermoelectromotive force of 1 mV/℃. A fairly large value was obtained. However, the electrical conductivity also decreases at the same time, and when a pn junction type thermocouple element is constructed, a pn junction is formed and it no longer exhibits ohmic properties. Therefore, when used as a power detection element, due to the rectification effect, a proportional relationship between the detection level and the output does not hold, and a correction circuit is required. Also, in order to eliminate this rectification effect, p-
Attempts have also been made to insert or cover the n-junction with a metal film, but in this case, a new Schottky junction is formed. Furthermore, in order to eliminate this Schottky junction, it is necessary to dope the carrier at the junction with the metal film to a high concentration using ion implantation or the like, making the device fabrication method extremely complicated. Furthermore, since the element resistance increases, thermal noise due to the resistance increases, limiting the minimum detection level.

Therefore, in order to improve the above-mentioned drawbacks of amorphous thin film semiconductors as thermoelectric materials, that is, the thermoelectromotive force is large but the electrical conductivity is low, it is necessary to increase the electrical conductivity by changing the composition of the material. For example, by adding Ni to an amorphous semiconductor material such as As, they succeeded in increasing the conductivity to 3 × 10 ⁰ [Ω cm] ^-1 , but unfortunately, The Seebeck coefficient, or thermoelectric power, was only 50 μV/°C, which is as low as that of metals (for example, JP-A No. 53-
143180).

[Problem to be solved by the invention]

In view of the above points, since both electrical conductivity and thermoelectric power are high, and the p ⁺ -n ⁺ junction has ohmic characteristics, there is no need to interpose an ohmic electrode between the p-n junction, and in addition p ⁺ type and n ⁺ type, which are easy to form thin films and have fine processing properties.
It is an object of the present invention to discover amorphous semiconductor thin films and to realize thermocouple elements that combine them, especially power detection elements that are inexpensive, small, have a wide measurable frequency range, have fast response, and are highly sensitive. This is a challenge.

[Means to solve the problem]

In the present invention ^, amorphous semiconductor thin films with ^high conductivity are newly discovered by the inventor. Focusing on microfabrication, we developed a high-performance, inexpensive thermocouple element with a new structure that does not require an ohmic electrode between p-n junctions, and a compact thermocouple element that uses this thermocouple element, has low element resistance, and has a wide measurement frequency range. This problem is solved by realizing a wide-ranging, fast-responsive, and highly sensitive power detection element.

〔Example〕

Figures 1 and 2 show the thermoelectric power - conductivity characteristics and temperature difference - of p ⁺ type and n ⁺ type semiconductor thin films newly discovered by the inventor that have large thermoelectric power and high conductivity.
FIG. 3 is a diagram showing thermoelectromotive force characteristics. It is characterized by being composed of an amorphous Si thin film (a-Si-F-H) synthesized from a mixed gas of SiF ₄ and H ₂ by the DC glow discharge method ^. Also,
The + mark indicates the characteristics of the n ⁺ shape. Thermopower α is positive in p ⁺ form,
Negative in n ⁺ form. Doping gases for forming p ⁺ type thin films and n ⁺ type thin films include B ₂ H ₆ and
_PH3 was used. As for the thermoelectric power, the absolute value is p ⁺ type.
200μV/℃ or more, n ⁺ type shows 150μV/℃ or more,
The p ⁺ and n ⁺ forms exhibit opposite polarities.

The thermopower (α) of p ⁺ −n ⁺ junction type is 350μV/
℃ has been obtained. Also, the conductivity (σ) at this time
is as large as 20 (Ω・cm) ^-1 or more.

Figure 2 shows metal electrodes provided at both ends of the p ⁺ type and n ⁺ type thin films, the cold junction side being at room temperature, the hot junction being at high temperature, and the temperature difference ΔT between the hot junction and the cold junction (room temperature).
The graph shows the relationship between thermoelectromotive force Vth and thermoelectromotive force Vth. In FIG. 2, the solid line indicates the characteristics of the p ⁺ type, and the dashed line indicates the characteristics of the n ⁺ type, with the p ⁺ type indicating positive and the n ⁺ type indicating negative.
As will be described later, good linearity can be obtained even without providing an ohmic electrode between the p ⁺ -n ⁺ junctions.

From the above experimental results, it was found that both the amorphous semiconductor thin film and the a·Si-F-H thin film exhibit excellent properties as thermocouple element materials.

3 and 4 are diagrams showing the configuration of an embodiment of a thermocouple element according to the present invention, and FIG. 3 shows a plan view.
FIG. 4 shows a sectional view taken along line X-X'. FIG. 3 and FIG. 4 show an insulating substrate 1, a first amorphous semiconductor 2 provided on the substrate, and a part of the insulating substrate 1 that is partially ohmic with respect to the first amorphous semiconductor provided on the substrate. a second amorphous semiconductor 4 forming a junction 3 having a characteristic, and a pair of ohmic electrodes 5 provided in contact with parts of the first and second amorphous semiconductors, isolated from the junction. , 6 and each amorphous semiconductor 2, 4
2 is a diagram showing a thermocouple element 9 composed of a contact portion 7, 8 with each ohmic electrode 5, 6. FIG. In this thermocouple element 9, the junction 3 between the first amorphous semiconductor and the second amorphous semiconductor is hot (cold).
Since each contact portion 7, 8 between each amorphous semiconductor and each ohmic electrode forms a cold (hot) contact, the temperature difference ΔT (°C) between the hot (cold) contact and the cold (warm) contact is DC thermoelectromotive force Vth (mv) proportional to
occurs between the pair of ohmic electrodes 5 and 6. The thermoelectromotive force Vth generated at this time is determined by the thermoelectric capacities α ₁ and α ₂ of the first and second amorphous semiconductor thin films and the temperature difference ΔT, and is given by the following equation.

Vth = (α ₁ + α ₂ ) ΔT ………(1) From the experimental results shown in Figure 1, p ⁺ type and n ⁺ type a・Si−F−H thin films were used as the first and second amorphous semiconductor thin films. If used, p ⁺ form and n ⁺
Since the shapes have thermoelectric powers with opposite polarities, a thermoelectromotive force Vth of 0.35 mv or more can be obtained per temperature difference ΔT=1°C.

5 and 6 are diagrams showing other embodiments of the thermocouple element according to the present invention, with FIG. 5 showing a plan view and FIG. 6 showing a front view. 5 and 6 show an insulating substrate 10, a first amorphous semiconductor 11 provided on the substrate, and a first amorphous semiconductor 11 provided on the substrate,
A second amorphous semiconductor 13 that forms a junction 12 with the first amorphous semiconductor, a portion of which has ohmic characteristics, and a second amorphous semiconductor 13 that is separated from the junction and is connected to the first and second amorphous semiconductors. A pair of ohmic electrodes 14, 15 provided in contact with the respective amorphous semiconductors 11,
13 and contact portions 16 and 17 with respective ohmic electrodes 14 and 15. FIG. In this thermocouple element 18, the junction between the first amorphous semiconductor and the second amorphous semiconductor forms a hot (cold) contact, and the contact areas 16 and 17 between each amorphous semiconductor and each ohmic electrode form a cold (hot) contact. form a contact point. As the first and second amorphous semiconductors, p ⁺ type and n ⁺ type a/Si-
If F-H thin film is used, temperature difference ΔT = approx.
A thermoelectromotive force Vth of 0.35 mv is obtained.

Since the thermocouple element 18 having the structure shown in this embodiment can be miniaturized by photoetching technology, it can be used for temperature measurement in a narrow space or as an element for measuring the surface temperature of an IC. 7 and 8 are diagrams showing an embodiment of a power detection element according to the present invention, particularly a power detection element in a microwave band. Show the diagram. 7th
8 and 8 show the thermocouple element 9 shown in FIGS. 3 and 4, a resistor 19 that absorbs the measured power and generates heat, and an input terminal 20 that supplies the measured power to the resistor 19. , is a diagram showing a power detection element 22 having a structure in which a ground terminal 21 is added, and the resistor 19 is
Opposite insulating substrate 1 corresponding to p ⁺ −n ⁺ junction 3
It is characterized by being provided on the top.

In this case, the heat generating part where the shape of the resistor is tapered is highest at the p ⁺ −n ⁺ junction 3 that forms the hot junction.
Each ohmic electrode 5, 6 forming a cold contact and each contact portion 7, 8 of each amorphous semiconductor 2, 4 are arranged so as to be at the lowest level. Since heat is generated in the resistor 19 in proportion to the magnitude P of the measured power,
The temperature difference ΔT between the hot junction Th and the cold junction Tc is proportional to the power P to be measured. On the other hand, when the temperature ^difference ΔT is given, the DC thermoelectromotive force Vth is expressed as ( _α ^p _{+ α o} ) and the temperature difference ΔT.

From the above, the DC thermal power Vth brought between the ohmic electrode pair 5 and 6 due to absorption and heat generation of the measured power P by the resistor 19 is given by the following equation.

Vth = (α _p + α _o ) ΔT∝ (α _p + α _o ) P ......(2) From equation (2), the magnitude of the measured power P is calculated between the ohmic electrode pair 5 and 6 of the thermocouple element. Obtained by measuring DC voltage.

When the magnitude P of the power to be measured is constant, the hot junction of the thermocouple element is given by the temperature Th of the p ⁺ -n ⁺ junction 3, and in order to increase the temperature of the p ⁺ -n ⁺ junction 3, In addition to reducing the shape of the heat generating portion of the resistor, it is necessary to suppress the amount of heat dissipated through the insulating substrate 1, the p ⁺ type and n ⁺ type thin films 2 and 4, and the surrounding air. Therefore, it is desirable for the insulating substrate 1 to be made of a material that has low thermal conductivity and can be processed into a thin material, such as Corning 7059 or fused silica glass. In order to speed up the response of the power detection element, a material with a small specific heat, that is, a material with a small heat capacity, such as sapphire, is used for the insulating substrate.

In addition, the p ⁺ -n ⁺ junction type a/Si-F-H thin film has ohmic properties and does not exhibit rectification properties, so p ⁺ -
Since there is no need to provide an ohmic electrode metal between the n ⁺ junctions, there is no increase in parasitic reactance when measuring microwave power, so the input standing wave ratio can be kept low even in the ultra-high frequency band. has advantages.

9 and 10 are views showing an embodiment of an optical power detection element to which the present invention is applied, with FIG. 9 showing a plan view and FIG. 10 showing a sectional view taken along line X-X'.

9 and 10 show optical power detection having the same cross-sectional structure as that of the thermocouple element shown in FIGS. 3 and 4, in which a light absorption film 31 is provided over the p ⁺ -n ⁺ junction. 3 is a diagram showing an element 32. FIG. However, in this case, the beam diameter of the object to be measured is about 1.5 to 2.0 mmφ, so the size of the light receiving surface needs to be about 3 to 5 mmφ, and the detection sensitivity remains the same even if the light receiving position moves within the light receiving surface. Requires characteristics. For this reason, it is advantageous to have a circularly symmetrical structure. Light absorption film 31
is composed of gold black, carbon black, or amorphous semiconductor thin films with different composition ratios.

The thermocouple element, the power detection element applying the thermocouple element, and the optical power detection element described in the above embodiments each have a configuration of a pair of thermocouple elements, but as can be easily imagined in terms of structure, 2
It is possible to construct a multi-pair thermocouple element in which more than one pair is connected in a cascade, a power detection element, and an optical power detection element by applying them, and in this case, the output voltage (thermoelectromotive force) between ohmic electrodes
Since Vth and output impedance each increase in proportion to the number of thermocouple elements, it is possible to design according to measurement accuracy and desired output impedance. Next, we will discuss the manufacturing method. A low-resistance amorphous semiconductor thin film is produced by applying a mixed gas of SiF ₄ and H ₂ .
It is common to add B ₂ H ₆ , AsH ₃ , PH _{3 ,} etc. as a doping gas and fabricate using the DC glow discharge method or plasma CVD method, but SiH ₄ gas
A low-resistance amorphous semiconductor thin film having similar characteristics can also be produced using a plasma CVD method in which B ₂ H ₆ , PH ₃ , AsH _{3 ,} etc. are added and a magnetic field or high power is applied. In the above amorphous semiconductor thin film, a part becomes microcrystals and becomes a microcrystalline semiconductor film, but since it has characteristics such as high electrical conductivity and high thermoelectric power, it can be used as a thermocouple element as described in the present invention. The characteristics are not lost. After depositing an amorphous semiconductor thin film on an insulating substrate, devices can be easily manufactured using photoetching techniques, metal vacuum evaporation methods, and the like. NiCr, Ta ₂ N, W, etc. are used as the resistance material.

〔Effect of the invention〕

Next, the effects of the present invention will be described.

(1) An inexpensive and highly sensitive thermocouple element that uses an amorphous semiconductor thin film with high thermoelectric power and high conductivity, eliminating the need for an ohmic electrode between the p-n junction, and thus simplifying the manufacturing process; A power detection element and an optical power detection element can be constructed by applying this thermocouple element. Particularly when measuring power higher than microwaves, the p ⁺ -n ⁺ junction type thin film structure power detection element does not require a metal electrode to take ohmic contact at the p ⁺ -n ⁺ junction, so parasitic reactance is small.
As a result, it is possible to manufacture a power detection element with a low input standing wave ratio, that is, a power detection element that can be used up to ultra-high frequency bands.

(2) When p ⁺ type and n ⁺ type a・Si−F−H (and a・Si−H) thin films are used as amorphous semiconductor thin films, the p ⁺ −n ⁺ junction exhibits ohmic properties, and moreover, Since the polarity of the thermoelectromotive force is opposite, the p ⁺ −n ⁺ junction type is given by the sum of the absolute values of the p ⁺ type and n ⁺ type thermoelectromotive force, so it is possible to construct a thermocouple element with a large thermoelectromotive force.

(3) Since microfabrication technology represented by photoetching technology can be used, it is possible to construct thermocouple elements etc. that are ultra-small and have a fast response speed (about 1 msec).

(4) Since the manufacturing method is easy, inexpensive thermocouple elements etc. can be manufactured.

As described above, the thermocouple element according to the present invention and the power detection element and optical power detection element to which this thermocouple element is applied have many advantages over conventional ones.

[Brief explanation of drawings]

FIG. 1 shows the thermoelectric power-conductivity characteristics of p ⁺ type and n ⁺ type a.Si-F-H thin films. FIG. 2 shows the temperature difference-thermoelectromotive force characteristics of p ⁺ type and n ⁺ type a-Si-F-H thin films. 3 and 4 are views showing one embodiment of a thermocouple element according to the present invention, with FIG. 3 showing a plan view and FIG. 4 showing a sectional view taken along line X-X' in FIG. 3. Fifth
6 are views showing another embodiment of the thermocouple element, FIG. 5 is a plan view, and FIG. 6 is a front view. 7th
8 are diagrams showing an embodiment of a power detection element to which a thermocouple element according to the present invention is applied, FIG. 7 is a plan view, and FIG. 8 is a sectional view taken along line X-X' in FIG. show.
9 and 10 are diagrams showing an embodiment of an optical power detection element to which a thermocouple element according to the present invention is applied. FIG. 9 is a plan view, and FIG. A cross-sectional view is shown. In the drawing, 1 , 10, 23 are insulating substrates, 2, 1
1, 24 are first amorphous semiconductors, 3 , 1
2, 25 are ohmic joints, 4 , 13, 26
is the second amorphous semiconductor, 5 , 6 , 14, 1
5, 27, 28 are each Ohmic electrodes, and 7 , 8 ,
16, 17, 29, and 30 are contact portions between each amorphous semiconductor and each ohmic electrode, 9 and 18 are respective thermocouple elements, 19 is a resistor, 20 is an input terminal, and 21
2 is a ground terminal, 22 is a power detection element, 31 is a light absorption thin film, and 32 is an optical power detection element.

Claims (1)

[Claims] 1 an insulating substrate 1; a first insulating substrate provided on the substrate;
a p ⁺ (or n ⁺ ) amorphous semiconductor 2; a p + (or n + ) amorphous semiconductor 2 provided on the substrate, a part of which has ohmic characteristics with respect to the first amorphous semiconductor ^;
- a second n ⁺ (or p ⁺ ) amorphous semiconductor 4 forming an n ⁺ junction 3; provided in isolation from the junction and in contact with a portion of the first and second amorphous semiconductors; A pair of ohmic electrodes 5 and 6
A p ⁺ −n ⁺ type thermocouple element comprising: a junction between the first amorphous semiconductor and the second amorphous semiconductor as a hot (cold) contact;
A thermocouple element characterized in that each contact portion 7, 8 between each amorphous semiconductor and each ohmic electrode is a cold (hot) contact.