JPH08148704A - Photoconductor and its manufacture - Google Patents

Abstract

PURPOSE: To reduce the capacitance and ON resistance between electrodes by forming the metal thin film of the electrodes with an extremely thin film and forming the metal thin film of a transmission line with a thick thin film. CONSTITUTION: Transmission lines 15A and 15B of Au thin film are thickly formed on a semi-insulating substrate 10 of InP substrate where Fe which is, for example, approximately 1×2mm square is doped and electrodes 16A and 16B are formed to be extremely thin near the center. The transmission line is set to approximately 10μm thick and the electrode is set to 0.1μm or less thick, which are 1/5 or less of the conventional thickness. Therefore, the surface area of the opposing electrode is reduced to 1/5 or less, thus reducing the capacity to approximately 1/5 or less. Since the thickness of the electrode is reduced to 1/5, the gap width of the electrode is reduced to approximately 1/5 and the ON resistance during ON can also be reduced.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a semi-insulating substrate which becomes a conductor by irradiating light, for example, an InP (Indium Phosphorus) substrate doped with Fe (iron), and electrodes which are separated by a metal thin film with a minimum interval. And a method for manufacturing the same.

[0002]

2. Description of the Related Art For example, a photoconductor relating to the present application is disclosed in Japanese Patent Application No. 5-190450, entitled "Optical Beam Shape Measuring Device," filed earlier by the present applicant. According to this, as a means for solving the problem, "a photoconductor having a pair of electrodes formed at an interval smaller than the diameter of the light beam to be measured is provided on the light receiving surface, and the photoconductor receives the light. The light beam to be measured is incident on the surface, and the light beam to be measured and the photoconductor are moved relatively by the scanning means in the arrangement direction of the electrodes, and the resistance value between the electrodes at that time is measured by the resistance measuring means. , ... ”, and FIG. 1B shows an enlarged plan view showing an example of the light receiving surface of the photoconductor.

A perspective view of the same photoconductor is shown in FIG. For example, on an InP semi-insulating substrate 10 doped with Fe having a size of about 1 × 2 mm square, Au (gold)
The transmission lines 12A and 12B are made of a strip line or a coplanar line by using a metal thin film such as. Electrodes 11A and 11B having a narrow gap width are formed in the central portion thereof. In the electrode structure, for example, the electrode width is 400 μm and the gap width is about 3 μm, but the electrode width and the gap width can be made smaller. Lead wires 1 are provided at the terminals of the transmission lines 12A and 12B, respectively.
3A and 13B are connected and connected to a connector, a bias voltage or an electric signal is applied to one connector, and an electric signal is sent from the other connector.

The semi-insulating substrate 10 is usually an insulator, and no current flows between the electrodes 11A and 11B. However, when the light to be measured is applied between the electrodes 11A and 11B, the semi-insulating substrate 10 enters the semi-insulating substrate 10. Carriers are generated and become conductors, and a current flows between the electrodes 11A and 11B. Therefore, it is possible to measure the shape of the switch, the mixer, the irradiated measured light beam,
It can be used as a photoconductor for various purposes such as a short pulse generator for converting an extremely short pulse of light into an extremely short pulse of electricity.

[0005]

In order to improve the performance of the photoconductor, it is necessary to reduce the ON resistance when the electrodes 11A and 11B are conductive and the interelectrode capacitance when insulating. is there. Since the value of the ON resistance is proportional to the square of the gap width L between the electrodes, it is necessary to reduce the gap width L in order to obtain a low ON resistance. When this photoconductor is used as a mixer, the ON resistance must be 41Ω or less and the gap width must be 2 μm or less because the loss of S ₂₁ must be 5 dB or less.

On the other hand, the capacitance between the electrodes, which determines the insulation characteristic when OFF, increases in inverse proportion to the gap width L.
It has a relationship that is contrary to the N resistance. Since the dynamic range of the signal to be sent is determined by the ON resistance at the time of ON and the insulation characteristic at the time of OFF, it is necessary to make the interelectrode capacitance as small as possible so as to increase the dynamic range. The present invention is a photoconductor in which the capacitance between the electrodes is extremely small and the ON resistance is also small, and a manufacturing method thereof.

[0007]

According to the present invention, the metal thin film of the electrode portion is formed by the ultimate thin film. Since the inter-electrode capacitance is proportional to the area of the electrodes facing each other, for example, if the film thickness is set to ⅕ times, the area of the opposing parts of the electrodes will be ⅕ times and the capacity will also be about ⅕ times. Because it becomes very small. Also, by making the film thickness thinner, it is easy to make by microfabrication by the lift-off method, it is easy to make an electrode with a narrow gap width of about 1 μm, and it is also possible to make an electrode with a narrower gap width.
There is also an advantage that the ON resistance at the time can be made smaller.

However, if the transmission line connected to the electrodes is made as thin as the electrodes, problems will occur in terms of characteristics and mounting. That is, the strength of the transmission line becomes weak, and there is a possibility that the transmission line will be broken or peeled off. When the lead wire is connected by bonding or soldering, there are few metal parts, so that the lead wire cannot be connected or is peeled off, or the metal is eaten when soldering. Since the cross-sectional area of the metal portion is small, the electric resistance is large and the conductor loss is large.

Therefore, only the narrow electrode portion is made of an ultrathin thin film, and the transmission line portion is made of a relatively thick thin film.
To increase the thickness of the transmission line, the transmission line portion may be plated with the same metal. That is, by masking the electrode portion with a resist and plating the transmission line, a desired thickness can be obtained, and the above-mentioned drawbacks can be eliminated. The electrode part
It is also possible to provide a plurality of stages in series, and in this case, the transmission line connecting between the plurality of electrodes is also formed of a relatively thick thin film.

The manufacturing method initially uses a lift-off method in which a normal photolithography process is used. However, when depositing a metal for electrode formation, the time is shortened to a fraction of that of the conventional method, and the film thickness is minimized. Control. Next, the transmission line except the electrode portion is plated with the same metal to make it relatively thick. At the time of subsequent mounting, the lead wire is bonded or soldered to the end of the transmission line to be connected to the connector.

[0011]

FIG. 1 shows an embodiment of the present invention. The parts corresponding to those in FIG. 3 are designated by the same reference numerals. For example, on the semi-insulating substrate 10 of InP substrate doped with Fe of about 1 × 2 mm square, the transmission lines 15A and 15B of Au thin film are made of thicker thin films, and the electrodes 16A and 16B are very thin near the center thereof. It is composed of a thin film. The thickness of the conventional transmission line and the electrode is about 0.5 μm, but in the present invention, the thickness of the transmission line is 0.5 μm or more and 10 μm or more.
The thickness of the electrode is set to about 0.1 μm, which is 0.5 μm or less, or less than ⅕ of the conventional thickness. Therefore, the surface area of the opposing electrodes was reduced to ⅕ times or less, and the capacity was also reduced to ⅕ times or less. Further, since the electrode gap width is ⅕ times the electrode thickness, the gap width can be reduced by about ⅕ times.

The transmission line is 1 compared to the conventional 0.5 μm.
Since the thickness is 0 times or more, the bonding and soldering processes for mounting are easy, the strength is high, and the electric resistance is small, so that the electrical loss is small. The transmission line and the electrodes have a high frequency characteristic impedance of 50
The line width of the coplanar line can be made narrower than that of the strip line and the surface area of the opposing electrodes becomes smaller than that of the strip line. Therefore, the coplanar line is more advantageous in reducing the interelectrode capacitance. is there.

(Other Embodiment) FIG. 2 shows another embodiment.
The embodiment of FIG. 2 is an example in which other electrodes 17A and 17B are formed in series with the electrodes 16A and 16B. This type of photoconductor is used as a photoconductor of a measuring instrument disclosed in, for example, Japanese Patent Application No. 6-211764, "Optical pulse shape measuring instrument". According to this, "of the two pairs of electrodes, one electrode operates as a detector for photoelectrically converting the light pulse waveform, and while the above-mentioned light pulse wave is slightly shifted by the delay means, the other electrode is separated from the one electrode. Is a photoconductor that samples the electrical signal of to extract the autocorrelation waveform.

In the photoconductor of FIG. 2 having two pairs of electrodes, two pairs of electrodes 16A, 16B and 17A, 1
Only the portion 7B is made of an extremely thin thin film, and the other transmission lines 15A, 15B and 15C are made of a relatively thick thin film. And the terminals are leads 13A and 13B,
Although not shown, it is connected to the connector.

Up to now, the electrodes 16A and 16B have been described as facing electrodes, but the invention is not limited to this. Even in the case of comb-shaped electrodes configured to fit teeth in the shape of a pair of comb teeth, or in other shapes, the capacitance can be reduced and the gap width can be narrowed by making the electrode part a very thin film The resistance can be lowered.

(Manufacturing Method) The manufacturing method is the lift-off method and the plating method using the photolithography method described in the above-mentioned Japanese Patent Application No. 6-189853, “Method for manufacturing minute parts using substrate”. To do. A brief description will be given below.

A conventional lift-off method is used. Photoresist is evenly coated on the semi-insulating substrate 10 and baked to form electrodes 16A and 16B and transmission lines 15A and 1B.
A 5B pattern photomask is positioned and exposed. After the exposure, the photoresist in the portion where the metal film such as the electrode and the transmission line is vapor-deposited is peeled off and the metal film is vapor-deposited.
This vapor deposition time is conventionally shortened to a fraction of the time so that the film thickness is 0.1 μm or less. The electrodes 16A and 16B are formed by peeling the photoresist under the metal film from the semi-insulating substrate 10 using a dedicated peeling liquid after vapor deposition.

Photoresist is evenly coated again and baked, and a photomask having a pattern for masking only the electrodes 16A and 16B is positioned and exposed. After the exposure, the photoresist of the portion to be plated other than the electrodes 16A and 16B is peeled off and plated to form transmission lines 15A and 15B of a relatively thick thin film of 0.5 μm or more.

[0019]

As described in detail above, according to the present invention, the electrode portions (16A, 16B) of the photoconductor are formed.
Is extremely thin and the transmission lines (15A, 15B) are thicker than before, so that the interelectrode capacitance is several times smaller than before. Since the electrode portion is made extremely thin, the gap width can be easily created by the lift-off method, and the gap width can be made even narrower, and the ON resistance can be further reduced. Therefore, the dynamic range can be increased by reducing the ON resistance and the interelectrode capacitance. The strength became stronger by thickening the transmission line. Bonding and soldering to transmission lines has become easier. The electrical resistance of the transmission line has decreased.
Manufacturing is generally easier. It has many advantages, and its technical and mass production effects are great.

[Brief description of drawings]

FIG. 1 is a perspective view of an embodiment of the present invention.

FIG. 2 is a perspective view of another embodiment of the present invention.

FIG. 3 is a perspective view of a conventional example.

[Explanation of symbols]

 10 semi-insulating substrate 11A, 11B electrode 12A, 12B transmission line 13A, 13B lead wire 15A, 15B, 15C transmission line 16A, 16B electrode 17A, 17B electrode

Claims (3)

[Claims] 1. A narrow gap width electrode (16A, 16B) formed of a metal thin film on a semi-insulating substrate (10) which becomes a conductor when irradiated with light, and the electrode (16A,
16B) has a transmission line (15A, 15B) formed of a metal thin film, the metal thin film of the electrodes (16A, 16B) is formed of an ultra-thin film. 15B) The metal thin film is formed of a thick thin film. 2. The electrode (16A, 16B) according to claim 1.
Is a multi-stage electrode (16A, 16B and 17A, 17B)
And the plurality of electrodes (16A, 16B and 17)
A photoconductor characterized by being configured in series via a transmission line (15C) connecting A, 17B). 3. An electrode (16A, 16B) having a narrow gap width formed of a metal thin film on a semi-insulating substrate (10) which becomes a conductor when irradiated with light, and the electrode (16A,
16B), a photoconductor having a transmission line (15A, 15B) formed of a metal thin film connected to the electrode (16A, 16B) and the transmission line (15B).
A, 15B) and a first step of forming an ultra-thin film using a lift-off method, and masking the electrode (16A, 16B) portion with a resist, and plating the transmission line (15A, 15B) to form a thick thin film. And a second step of: