JPH021379B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention uses a thermocouple element, particularly an amorphous semiconductor thin film and a metal resistor thin film, which have a large thermoelectric power and are characterized by ease of thin film formation and ease of microfabrication. The present invention relates to a thermocouple element equipped with a thermocouple element, which is used for power detection ranging from low frequencies to light waves, with consideration given to low input impedance, particularly impedance matching in the high frequency region.

Generally, an amorphous semiconductor refers to a semiconductor that is a substance excluding liquids and gases and does not exhibit three-dimensional periodicity crystallographically. In other words, it is defined as a semiconductor that is irregular and amorphous and does not have a diffraction peak that can be identified in an X-ray diffraction pattern. The term also includes semiconductors that are

Traditionally, when measuring power, especially high-frequency power,
A bolometer is used as the detection element, and recently thin film thermocouple elements such as Bi-Sb and other
A semiconductor thin film thermocouple element represented by Si-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. This caused the zero point to fluctuate, necessitating a circuit to compensate for this zero point drift. Moreover, in the case of a thermistor,
As the frequency increases, the input standing wave ratio increases,
Additionally, the barrette has drawbacks such as being susceptible to overcurrent.

In a 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 thermoelectromotive force proportional to the incident power. It is measured by converting it into Although this method has a small zero point drift due to changes in ambient temperature, it is difficult to measure small amounts of power below 1 μW. especially
In the case of thin film thermocouple elements such as Bi-Sb,
The melting point of the metal is low, and especially when a polyimide film is deposited on an insulating substrate such as mica, the adhesion to the insulating substrate becomes weak. Furthermore, since the film quality is impaired by water or organic solvents, there are drawbacks such as the inability to use microfabrication techniques such as photoetching techniques. On the other hand, Si−
The semiconductor-thin film thermocouple element represented by Ta ₂ N is
Thermal conductivity of silicon (Si) of the support substrate is 1.45W/
As large as cm℃. Therefore, in order to increase the detection sensitivity of the thermocouple element, it is necessary to make the silicon substrate thinner, and the substrate thickness for a practical element is about 5 μm. Since a selective etching technique is usually used to thin a part of a chip-shaped silicon substrate, it is necessary to form an etching stopper diffusion layer on the silicon substrate in advance. As described above, the semiconductor-thin film thermocouple element has a complicated structure and is also difficult to manufacture.

Therefore, the applicants of the present invention have focused on the large thermoelectric power of amorphous semiconductor thin films, particularly amorphous silicon thin films (hereinafter referred to as amorphous Si thin films), the ohmic properties of the P ⁺ -n ⁺ junction, the ease of thin film formation, and the microfabrication. Focusing on the properties of the thermocouple, the authors have previously proposed a thermocouple element composed of first and second amorphous semiconductor thin films, some of which form a contact portion with ohmic characteristics, on an insulating substrate. .

Although there is no problem in detecting optical power using the thermocouple element composed of the first and second amorphous semiconductor thin films, for example, if microwave power is directly input to the thermocouple element, When detecting incident power using a method in which thermoelectric conversion is performed using a sensor, impedance matching must be achieved. However, in the thermocouple element, although the conductivity of the first and second amorphous semiconductor thin films constituting the thermocouple element can be made higher than in the past, the conductivity is still sufficient to detect high-frequency power. A thin film was not obtained. Therefore, the input impedance of the thermocouple element is still high, and impedance matching cannot be achieved. It would be better to increase the conductivity of the amorphous semiconductor thin film, but with the current technology, it is possible to realize an amorphous semiconductor thin film with high conductivity (σ), for example, 10 ² S cm ^-1 or more in the P ⁺ type. It is not realized in ⁺ form.

Therefore, it is possible to manufacture a thermocouple element by forming a thin film with a physical shape that reduces the input impedance. In this case, the input impedance can be made small in terms of direct current, and the impedance matching condition is satisfied, but in terms of alternating current, the input standing wave ratio increases, which is undesirable. Moreover, there is a drawback that the distance between the hot junction and the cold junction becomes short, which impairs its function as a thermocouple element.

The present invention has been made in view of the above points, and has a structure in which impedance matching can be achieved by replacing either the first or second amorphous semiconductor thin film with a metal resistor thin film having appropriate conductivity. An object of the present invention is to provide a thermocouple element and a power detection element using the thermocouple element. This will be explained below with reference to the drawings.

FIG. 1 is a plan view showing an embodiment of a thermocouple element according to the present invention, and FIG. 2 is a sectional view taken along arrow XX in FIG.

1 and 2, an amorphous semiconductor thin film 2 and a metal resistor thin film 3 are provided on an insulating substrate 1. As shown in FIGS. Parts of the amorphous semiconductor thin film 2 and the metal resistor thin film 3 are in contact with each other, forming a contact portion 5 having ohmic characteristics. As shown in the figure, the amorphous semiconductor thin film 2 and the metal resistor thin film 3 are provided with an ohmic electrode 4 and an electrode 4', which are separated from the contact portion 5 and are partially in contact with each other, forming a pair of electrodes. ing.

In the thermocouple element 7 configured in this way, the contact portion 5 between the amorphous semiconductor thin film 2 and the metal resistor thin film 3 serves as a hot (cold) contact, and the contact portion 6 between the amorphous semiconductor thin film 2 and the ohmic electrode 4 and the metal The contact portion 6' between the resistor thin film 3 and the electrode 4' serves as a cold (hot) contact, and a thermoelectromotive force V proportional to the temperature difference ΔT between the hot and cold contacts is applied to the ohmic electrode 4. and the electrode 4'. The thermal electromotive force V generated at this time is the amorphous semiconductor thin film 2
The thermoelectric power α _a of the metal resistor thin film 3, the thermoelectric power α _n of the metal resistor thin film 3,
It is determined by the above-mentioned temperature difference ΔT and is expressed as V=(α _a +α _n )ΔT (1).

As the amorphous semiconductor thin film 2, P ⁺ type or
If each n ⁺ type amorphous Si thin film is used, the thermoelectric power _{α a} of each P ⁺ and n ⁺ type amorphous Si thin film has an opposite thermoelectric power, so that the thermoelectric power generated between the ohmic electrode 4 and the electrode 4' is generated between the ohmic electrode 4 and the electrode 4'. The polarity of the thermoelectromotive force V is reversed.

When the P ⁺ type or n ⁺ type amorphous semiconductor is used as the amorphous semiconductor thin film 2, the combination with the metal resistor thin film 3 has a large Seebeck coefficient. To be elected. For example, when a P ⁺ type amorphous semiconductor thin film is used as the amorphous semiconductor thin film 2, a combination of constantan or nickel thin films is used as the metal resistor thin film.
When an n ⁺ type amorphous semiconductor thin film is used, it is generally combined with a nichrome thin film or the like as a metal resistor thin film.

On the other hand, the input impedance of the thermocouple element 7 is lowered by using the metal resistor thin film 3. The conductivity of the metal resistor used for the metal resistor thin film 3 is about one order of magnitude higher than the conductivity of the amorphous semiconductor used for the amorphous semiconductor thin film 2. Therefore, the thermoelectromotive force of the thermocouple element 7 according to the present invention is approximately lower than that in the case where the thermocouple element is constructed by providing a second amorphous semiconductor thin film on the illustrated metal resistor thin film 3. A thermocouple element with a structure capable of impedance matching is constructed, although it is only half of the size.

FIG. 3 is a plan view showing an embodiment of a power detection element to which the thermocouple element according to the present invention is applied;
The figure is a sectional view taken along arrow YY in FIG. 3.

3 and 4, the thermocouple elements according to the present invention explained in FIGS. 1 and 2 are arranged in parallel on an insulating substrate 11 with their directions reversed. That is, the amorphous semiconductor thin films 12 and 12' and the metal resistor thin films 13 and 13', which partially contact each other and form contact portions 15 and 15' having ohmic characteristics, are attached to the insulating substrate 1.
It is located on 1. As shown in the figure, the amorphous semiconductor thin film 12 and the metal resistor thin film 13' are
Ohmic electrodes 14A and 14C are provided at positions separated from each of the contact portions 15 and 15' and partially in contact with the contact portions 15 and 15'. In addition, each contact portion 15
and 15', the amorphous semiconductor thin film 12' and the metal resistor thin film 13 are partially in contact with each other, and an ohmic film above the amorphous semiconductor thin film 12' and the metal resistor thin film 13 is in contact with a part of the metal resistor thin film 13. Electrode 14B
is provided.

The power detection element 18 configured in this way includes an amorphous semiconductor thin film 12 and a metal resistor thin film 13.
contact portion 15 and amorphous semiconductor thin film 1
The contact area 15' between the metal resistor thin film 13' and the metal resistor thin film 13' becomes a hot junction, the contact area 16A between the amorphous semiconductor thin film 12 and the ohmic electrode 14A, and the contact area between the metal resistor thin film 13' and the electrode 14C. , and the contact portion 16B between the amorphous semiconductor thin film 12' and the metal resistor thin film 13 serve as cold contacts.

An example of a power detection device constructed using the power detection element 18 is shown in FIG. In Figure 5,
Reference numerals 14A, 14B, 14C, and 18 correspond to those in FIG. Reference numeral 20 indicates a signal to be measured, 21 indicates a coupling capacitor, 22 indicates a bypass capacitor, 23 indicates an amplifier, 24 indicates a display device, 25, 2
5' represents earth.

The signal to be measured inputted via the coupling capacitor 21 is directly absorbed within the power detection element 18, thermoelectrically converted, and its thermoelectromotive force appears between the output terminal ohmic electrodes 14A and 14C. As can be seen from FIG. 5, the input impedance of the power detection element 18 almost corresponds to one thermocouple element 7 explained in FIGS. 1 and 2, indicating that impedance matching is achieved. .

Ohmic electrodes 14A and 1 of power detection element 18
4B, and between the ohmic electrode 14B and the electrode 14C, a thermoelectromotive force shown by the formula (1) is generated, so a pair of thermocouple elements is provided between the ohmic electrode 14A and the electrode 14C. The sum of the electromotive forces generated in , that is, V=2(α _a +α _n )ΔT appears.
The sum of the electromotive forces is amplified by the amplifier 23 and then displayed on the display device 24.

Moreover, as can be seen from FIG. 5, the power detection element 18
Ohmic electrode 14A is grounded, and electrode 1
4C is grounded at high frequency via the bypass capacitor 22, and the stray inductance caused by the output terminal lead wire is not fed back to the signal system under test, so the input standing wave from low frequency to ultra-high frequency The ratio can be kept low and constant, and the power detection device configured using the power detection element 18 can therefore detect and measure power ranging from low frequencies to very high frequencies.

FIG. 6 is a plan view showing an embodiment of an optical power detection element to which a thermocouple element according to the present invention is applied;
FIG. 7 is a sectional view taken along arrow Z-Z in FIG. 6.

In FIGS. 6 and 7, numerals 1 to 7 correspond to those in FIGS. 1 and 2. Reference numeral 37 represents a light absorption film, and 38 represents an optical power detection element.

The optical power detection element 38 is a contact portion 5 between the amorphous semiconductor thin film 2 and the metal resistor thin film 3 that forms the hot junction of the thermocouple element 7 explained in FIGS. 1 and 2.
A light absorption film 37 is provided on the surface. The light absorption film 37 is made of gold black, carbon black, or an amorphous semiconductor thin film having a different composition ratio.

The thermocouple elements, power detection elements and optical power detection elements using the thermocouple elements described in the above embodiments have been described as having one or two pairs of thermocouple elements, respectively, but they can be easily constructed. As you can imagine, a multi-pair thermocouple element can be constructed by connecting one or more pairs in a cascade, and in this case, the output power (thermoelectromotive force) and input impedance between the ohmic electrodes are , each increase in size in proportion to the number of thermocouple elements, so it is possible to design according to measurement accuracy, desired input impedance, etc.

Next, a method for manufacturing the thermocouple element will be described. P type or n type is formed on the insulating substrate 1 using the glow discharge method.
After depositing the amorphous semiconductor thin film 2, a metal resistor thin film 3 is formed by vapor deposition or the like. For patterning, a photoetching technique or a metal mask is used. Next, an ohmic electrode 4 and an electrode 4' are provided on each portion of the P-type or n-type amorphous semiconductor thin film 2 and the metal resistor thin film 3. Ohmic electrode materials include Al, Au, W,
NiCr, Pt, etc. are used. In particular, as an example of electrode materials for amorphous semiconductor thin films, NiCr500Å/
A multilayer structure of Au3000Å is excellent.

The method for manufacturing the optical power detection element includes adding the light absorption film 3 to the process described in the method for manufacturing the thermocouple element.
7 is added. A glow discharge method, a vacuum evaporation method, or the like can be used to form the light absorption film. Next, we will briefly discuss the glow discharge method. Glow discharge methods include the DC glow discharge method, which generates glow discharge in a direct current electric field, and the RF glow discharge method, which generates glow discharge in a high frequency electric field. FIG. 8 shows an example of an apparatus for depositing an amorphous Si thin film on an insulating substrate or the like by the RF glow discharge method. This device consists of a vacuum container 40, an anode 44 and a cathode 45 arranged in parallel inside the vacuum container 40, an air supply port 41 and an exhaust port 42 for supplying or exhausting gas 43 into the vacuum container 40, an anode 44 and a cathode 45, Heater 4 that heats cathode 45
7, 47', etc. An insulating substrate 46 is placed on the anode 45. As gas 43,
Usually, a mixture gas of SiH ₄ or SiF ₄ and H ₂ to which a doping gas (for example, PH ₃ , AsH ₃ , B ₂ H ₆ , etc.) is added is used. The vacuum pressure during glow discharge is several
Torr, voltage E is a high frequency voltage, the voltage is almost constant and the current is 1 to 100 mA/cm ² ,
Most of the gas reactions occur within the positive column (plasma 48). In particular, in this glow discharge method, the substrate temperature
It has the characteristic that amorphous semiconductor thin films can be deposited at a low temperature of 400℃ or less (conventional pyrolysis methods for thin film production have a substrate temperature of 500℃ or less).
(700℃ was required). An example of deposition conditions using the DC glow discharge method is a discharge pressure of 0.1~
10Torr, discharge current 1-100mA/cm ² , discharge voltage
500~800V, electrode spacing 3cm, substrate temperature 250~450
°C, SiF ₄ /H ₂ = 1~10, B ₂ H ₆ /SiF ₄ = 100~
2500ppm, _PH3 / _SiF4 =100-2500ppm.
As an amorphous semiconductor thin film deposited under these conditions, a conductivity of σ = 20 (Ω·cm) ^-1 or higher is easily obtained. A common method for increasing the conductivity of a semiconductor thin film is to increase the discharge current or increase the proportion of doping gas. A method of applying a magnetic field is also effective. When a semiconductor thin film is deposited using the above method, the amorphous film contains a fine crystal phase of around 100 Å or exhibits polycrystalline properties, but the thermoelectric properties are maintained. In this way, semiconductors including those containing fine crystalline phases that maintain thermoelectric properties are included in the amorphous semiconductor defined at the beginning of this specification.

Further, Si-Ge alloy type amorphous semiconductor thin films can also have high conductivity. In this case, an amorphous semiconductor thin film is deposited using a mixed gas of GeH ₄ with a doping gas of B ₂ H ₆ or PH ₃ or AsH ₃ using an RF or DC glow discharge method.

As explained above, the present invention has the following effects.

(1) By combining an amorphous semiconductor with high thermoelectric power and high conductivity and a metal resistor with a different polarity of thermoelectric power, a thermocouple element that can perform impedance matching in the high frequency band can be constructed. By applying the paired elements, a direct heating type high frequency power detection device or the like can be constructed.

(2) Since microfabrication technology represented by photoetching technology can be used, it is possible to construct power detection elements, optical power detection elements, etc. that apply ultra-small thermocouple elements and the present thermocouple elements.

(3) Since the high-frequency power detection element, etc. can be constructed as a directly heated type, a single-sided power detection element is required compared to the conventional indirectly heated type, which reduces the number of manufacturing steps, resulting in cheaper power detection devices, etc. becomes possible.

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 is a plan view showing an embodiment of the thermocouple element according to the present invention, Fig. 2 is a cross-sectional view taken along arrow X-X in Fig. 1, and Fig. 3 is an application of the thermocouple element according to the present invention. FIG. 4 is a plan view showing an embodiment of the power detection element, FIG. 4 is a sectional view taken along arrow Y-Y in FIG. 3, and FIG. Fig. 6 is a plan view showing an embodiment of an optical power detection element using the thermocouple element according to the present invention, Fig. 7 is a sectional view taken along arrow Z-Z in Fig. 6, and Fig. 8 is a glow The figure which shows an example of the apparatus based on the discharge method. In the figure, 1, 11, 46 are each insulating substrate, 2, 1
2, 12' are each amorphous semiconductor thin film, 3, 1
3, 13' are each metal resistor thin film, 4, 14A, 1
4B is each ohmic electrode, 4' and 14C are each electrode,
5, 6, 6', 15, 16A, 16B, 35 are contact parts, 7 is a thermocouple element, 18 is a power detection element, 2
0 is the signal to be measured, 21 is the coupling capacitor, 22 is the bypass capacitor, 23 is the amplifier,
24 is a display device, 25 and 25' are ground, 37 is a light absorption film, 38 is an optical power detection element, 40 is a vacuum container, 41 is an air supply port, 42 is an exhaust port, 43 is a gas, 44 is an anode, 45 is the cathode, 47,4
7' represents each heater, and 48 represents plasma.

Claims (1)

[Claims] 1 an insulating substrate 1; an amorphous semiconductor thin film 2 provided on the insulating substrate 1; and an amorphous semiconductor thin film 2 provided on the insulating substrate 1;
a metal resistor thin film 3 formed in contact with a part of;
The amorphous semiconductor thin film 2 and the metal resistor thin film 3 each include an ohmic electrode 4 and an electrode 4' provided on each part of the amorphous semiconductor thin film 2 and the metal resistor thin film 3 in isolation from the contact portion 5. The contact portion 5 between the amorphous semiconductor thin film 2 and the metal resistor thin film 3 and the ohmic electrode 4 and the electrode 4' is used as a cold (hot) contact. A thermocouple element characterized in that an electromotive force is generated between the ohmic electrode 4 and the electrode 4'.