JPH05343434A - Mesfet and device utilizing the same - Google Patents

Abstract

PURPOSE:To obtain MESFET which does not show change of temperature and of current flowing between drain and source due to radiation of light, etc., by setting the lower part of an N type GaAs layer including drain, source and gate electrode forming positions as the P<-> layer, forming the P<++> type layer at the lower part of the P<-> layer and then forming a leadout electrode to the P<++> type layer. CONSTITUTION:An N type GaAs layer 3 is formed on a half-insulated GaAs substrate 1 and drain, source and gate electrodes 10, 5 are formed on such N type GaAs layer 3. In such MESFET, the lower part of the N type GaAs layer 3 including the electrodes 10, 5 forming region is set to the P<-> type layer 7, the P<++> type layer 8 is formed in the region under the P<-> type layer 7 and a leadout electrode 12 is formed to such P<++> type layer 8. For example, the P<++> type layer 8 is formed on the substrate 1 and the P<-> type layer 7 is formed thereon. Next, a buffer layer 2 and an operation layer 3 are formed, an InGaAs layer 9 is formed as a contact layer to the region which will become the source, drain and an electrode to is formed on the contact layer 9.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION The present invention relates to GaAs MESFE.
More specifically, the present invention relates to an improvement in the performance of T, and more particularly to a MESFET and a device using the same, in which the backgate effect is reduced.

[0002]

2. Description of the Related Art FIG. 9 is a sectional view showing a general structure of a MESFET. In the figure, 1 is a semi-insulating GaAs substrate, on which a buffer layer 2 and an operating layer 3 are provided.
Are formed. 4 is a source, 5 is a gate, and 6 is a drain. In the above structure, when a positive potential Vd is applied to the drain 6 with respect to the source 4, electrons flow from the source to the drain in the operating layer 3. Since the gate electrode is a Schottky barrier, the first depletion layer A extends in the operating region. By changing the gate voltage Vg, the depth of the first depletion layer A changes and the cross-sectional area of the channel. Changes, and the drain-source current Id changes.

FIG. 10 is a circuit diagram showing an example in which an active probe of a high frequency oscilloscope is constructed by using the above-mentioned conventional MESFET. In FIG. 10, Q1, Q
2 is a first and a second MESFET, the source of Q1 and the drain of Q2 are connected, and the third MESF is connected to the connection point.
The gate of ETQ3 is connected, the drain power source VDD is connected to the drain side of Q1 and the source power source VSS is connected to the source of Q2.
Are connected, and the gate of Q2 is connected to the source of Q2. The gate of Q1 is provided with an input terminal, and the source of Q3 is provided with an output terminal. In the above structure, Q1 and Q2 are buffer stages for increasing the input impedance, and Q2 functions as a constant current load of Q1. Q3 is an output stage for obtaining a current gain.

FIG. 11 shows a conventional example of a mixer.
Reference numeral 0 denotes a dual gate MESFET made of GaAs, which has an RF input terminal 40a and a first local oscillation input terminal 40.
b. Reference numeral 41 is a first impedance matching circuit connected to the drain power source VDD and also connected to the dual gate MESFET 40, and 42 is a matching circuit 4
2 is a first bandpass filter connected to the latter stage of the first band.
Reference numeral 45 is a Si transistor, the output of the bandpass filter 42 is input to the base, and resistors R1 and R are connected to the emitter.
The second local oscillation is input via the connection point of 2. The second impedance matching circuit 46 is connected to the collector of the Si transistor 45 on the input side.
A second bandpass filter 47 is connected in the subsequent stage to output a predetermined frequency. In the above structure, the portion surrounded by A including the dual gate FET 40 is for high frequency, and the portion surrounded by B including the Si transistor 45 functions for low frequency. In addition to these, an analog multiplier, bipolar transistor, etc. are also used as the mixing element.

[0005]

By the way, in the above-mentioned conventional MESFET, the drain current fluctuates due to the channel length modulation in the vertical direction caused by the leakage current of the semi-insulating substrate 1. This leakage current is caused by the charge trap in and out of the deep trap, forms a space charge region between the channel and the substrate, and is the same as the gate because of the space charge accumulated from the substrate 1 side in the velocity saturation region immediately below the gate. Similarly, the channel is depleted and the second depletion layer B is formed (this phenomenon is called the backgate effect). Since the back gate effect is related to deep traps, the characteristics change remarkably depending on temperature, light irradiation, and the like. Therefore, when the MESFET is applied to an analog and digital circuit such as a measuring instrument, it becomes an essential problem. In particular, when a DC-coupled line-type amplifier is formed, an abnormal change in gain is seen in the low-frequency region, and its characteristics also change significantly depending on the presence or absence of light irradiation. Conventionally, as a method of suppressing the backgate effect, a method of directly attaching a metal to the back side of the substrate 1 (backgate) and a method of increasing the resistance of the lower part of the operating layer (low temperature growth, etc.) are known. Satisfactory effect is not obtained.

The above-mentioned conventional GaAs MESFE is used.
When an active probe as shown in FIG. 10 is constructed using T, there is a problem that the DC drift is large due to the backgate effect and the low frequency characteristic is not stable. Further, when the mixer circuit shown in FIG. 11 is configured by using this GaAs MESFET, when it is desired to obtain frequencies over a wide range from high frequency to low frequency, the use frequency band of each element is limited. And two elements for low frequency are required. Generally, elements are formed on a GaAs substrate for high frequencies and on a Si substrate for low frequencies.
Therefore, there is a problem that these cannot be monolithically manufactured on the same substrate. The present invention is based on the conventional M
This was done in order to solve the problems in the ESFET and the device using the same, and the potential of the second depletion layer B shown in FIG. It is an object of the present invention to realize a MESFET with no change in the current flow and to provide a device using the MESFET.

[0007]

In order to solve the above-mentioned problems, according to the present invention, in claim 1, an n-type GaAs layer is formed on a semi-insulating GaAs substrate, and a drain and a semiconductor are formed on the n-type GaAs layer. -MESF with gate and gate electrodes
In ET, the n-type GaA including the electrode formation portion
The lower part of the s layer is a p ⁻ layer, the p ^{+ +} layer is formed under the p ⁻ layer, and the extraction electrode is formed on the p ^{+ +} layer. First and second
The source and the drain of the MESFET are connected, and the gate of the third MESFET is connected to the connection point, and the first FE is connected.
The drain power source is connected to the drain side of T and is connected to the second MESFE.
A source of power is connected to the source of T, and the first MESF is connected.
In an active probe having an input terminal at the gate of ET and an output terminal at the source of the third MESFET,
The MESFET according to claim 1 is used as the MESFET, the extraction electrodes of the first and third MESFETs are connected to respective sources, and the extraction electrode of the second MESFET is provided with a voltage correction input terminal. In the mixer for inputting and mixing the first and second frequencies, the MESFET according to claim 1 is used as a mixing element, and the M
It is characterized in that the first frequency is input to the gate of the ESFET, the second frequency is input to the extraction electrode, and an output terminal is provided on the drain side.

[0008]

With respect to claim 1, the potential of the second depletion layer is p ⁻ , p
It is taken out by the take-out electrode through the ⁺⁺ layer. The electrode is fixed at an arbitrary potential. This reduces changes in the drain-source current due to temperature changes and light irradiation. With respect to the second aspect, since the MESFET according to the first aspect is used, the DC characteristic is extremely stable and the high frequency characteristic is also provided, so that the electric signal can be transmitted over a wide band. With respect to the third aspect, since the same element can be designed over a wide band, the design is facilitated, monolithicization is possible, and the performance as a high frequency circuit is improved.

[0009]

DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. 1 is a sectional view showing the construction of an embodiment of the present invention. In FIG. 1, the same elements as those in FIG. 9 are designated by the same reference numerals, duplicate description is omitted, and wiring portions are also omitted. In this embodiment, first, a p ^{+ +} layer 8 having a thickness of about 0.5 to 1 μm is formed on the substrate 1, and a p ⁻ layer 7 is formed thereon to a thickness of, for example, about 1 to 2 μm. Next, the buffer layer 2 and the operation layer 3 are formed, the InGaAs layer 9 as a contact layer is formed in the portions to be the source and drain, and the electrode made of, for example, WSi / Au is formed on the contact layer. .. As the gate electrode 5, W / WSi is directly formed on the operating layer 3. Next, MESFET
A hole 11 is formed in the vicinity of, and an extraction electrode 12 reaching the surface of the substrate is formed in the hole 11.

According to the above structure, the potential of the second depletion layer can be set to zero potential by grounding the extraction electrode 12, for example, or can be fixed by connecting it to a place having an appropriate stable potential. It is possible to suppress changes and changes in the current (Id) between the drain and the source due to light irradiation or the like. 2 and 3 are comparative diagrams showing the characteristics of the GaAs MESFET with extraction electrode (hereinafter referred to as PG-FET) manufactured by the present inventors and the respective FETs without extraction electrode. 2A and 2B are diagrams showing the relationship between the back gate voltage and the rate of change in the drain-source current when the FET is irradiated with light. FIG. 2A is a case with an extraction electrode, and FIG. .. The back gate voltage represents the potential on the back side of the substrate when the source is used as a reference, and PG
-When measuring the FET, the extraction electrode was connected to the source electrode. The light irradiation (tungsten lamp) strongly activates deep level traps and other defects, which further increases the leakage current of the semi-insulating GaAs substrate and significantly lowers the insulating property. According to FIG. 2, it can be seen that the case with the extraction electrode is extremely stable regardless of the presence or absence of light irradiation, and is not affected by the back gate potential at all. Figure 3
Shows the relationship between the frequency and the rate of change of the drain output voltage in the low frequency region, which forms a DC amplifier with a gain of about 10 dB. (A) is the case with an extraction electrode, (b) is the case without an extraction electrode . According to the figure, the output voltage is 30 to 40% with respect to the change in frequency without the extraction electrode.
Although it varies to some extent, it is found to be extremely accurate and stable in the range of about 2% for the case with the extraction electrode. FIG. 4 is a sectional view showing the construction of another embodiment of the present invention. Figure 1
The length of the p ⁺⁺ layer is different from that of the above embodiment. That is, the drain by inserting the p ⁺⁺ layer - source - if increased capacitance between the scan is a problem the length of the p ⁺⁺ layer gate - and to the vicinity of bets of the depletion layer.

FIG. 5 is a circuit configuration diagram showing an embodiment according to claim 2 of the present invention. 5 is different from the conventional active probe (FIG. 8) in the first to third MESFs.
The PG-FET according to claim 1 is used as ET, and
The extraction electrodes of the third PG-FETs Q1 'and Q2' are connected to their respective sources, and the extraction electrodes of the third PG-FET Q3 'are connected to voltage correction input terminals. In the above configuration, Q2 'functions as a constant current load for Q1', and Q2 '
The fluctuation of the operating point of Q1 'can be suppressed by applying a predetermined voltage to the correction terminal 30 connected to the back gate. As a result, an active probe with less noise can be realized.

FIG. 6 is a circuit configuration diagram showing an embodiment according to claim 3 of the present invention. In FIG. 6, reference numeral 50 is a first bandpass filter to which an input signal (RF) is input, and 51 is a first impedance matching circuit connected to the subsequent stage. The output of the matching circuit 51 is biased so as to perform a linear operation via the connection point of the capacitor C1 and the resistors R1 and R2, and is connected to the gate of the PG-FET.

Reference numeral 52 is a second bandpass filter to which the local oscillation signal (LO) is input, and reference numeral 53 is a second impedance matching circuit connected to the subsequent stage. The output of the matching circuit 52 is biased so as to perform a non-linear operation via the connection point of the capacitor C2 and the resistors R3 and R4, and the PG-FET.
It is connected to 60 extraction electrodes. 56 is a third impedance matching circuit connected to the drain power source VDD and the drain side of the PG-FET 60, and 57 is a third bandpass filter connected to the subsequent stage of the matching circuit 56.

FIG. 7 shows changes in the depletion layer of the PG-FET in the above circuit. The current flowing between the drain and source of the PG-FET depends on the spread of the first depletion layer and the second depletion layer. It is determined. The spread of these depletion layers can be controlled by the gate-source voltage and the back-gate-source voltage. Therefore, if the input signal (RF) and the local oscillation signal (LO) are connected between the gate and the source and between the back gate and the source as shown in the figure, the first depletion layer and the second depletion layer are depleted. The layer changes as shown by the arrow, and the change changes the drain-source current. That is, the drain-source current, which changes in proportion to the change in the first depletion layer, is modulated by the change in the second depletion layer. The drain-source current includes the sum and difference components of the frequency that is a constant multiple of the RF signal and the frequency of a constant multiple of the LO signal, and the necessary component can be extracted from this.

[0015]

As described above in detail with reference to the embodiments, according to the MESFET of the present invention, the lower portion of the n-type GaAs layer including the electrode forming portion is a p ⁻ layer, and the p ⁻ layer is formed below the p ⁻ layer. Since the p ^{+ +} layer is formed and the extraction electrode is formed on the p ^{+ +} layer, it is possible to reduce the change in the drain-source current due to temperature change or light irradiation. In addition, it is possible to realize a MESFET in which all the extraction electrodes can be set to a fixed potential or can be easily separated and independently wired even when it is desired to be independent in terms of a circuit (for example, when feedback is applied). Also, the active probe using this PG-FET can realize accurate signal transmission over a wide band, and when a mixer is configured, a wide band mixing element can be formed on the same substrate, which facilitates design, The performance as a high frequency circuit can be improved.

[Brief description of drawings]

FIG. 1 is a configuration cross-sectional view showing one embodiment of a MESFET of the present invention.

FIG. 2 is a diagram showing a relationship between a back gate voltage and a change rate of a drain-source current when a MESFET of the present invention and a conventional MESFET are irradiated with light.

FIG. 3 is a diagram showing a relationship between a frequency and a change rate of a drain output voltage in a low frequency region of the MESFET of the present invention and the conventional MESFET.

FIG. 4 is a sectional view showing the configuration of another embodiment of the MESFET of the present invention.

FIG. 5 is a circuit configuration diagram showing an embodiment in which the MESFET of the present invention is used for an active filter.

FIG. 6 is a circuit configuration diagram showing an embodiment using the MESFET of the present invention as a mixer.

FIG. 7 is a diagram showing changes in the depletion layer when the MESFET of the present invention is used in a mixer.

FIG. 8 is a circuit configuration diagram showing another embodiment using the MESFET of the present invention as a mixer.

FIG. 9 is a cross-sectional view showing a general configuration of MESFET.

FIG. 10 is a circuit configuration diagram showing a conventional example of an active filter.

FIG. 11 is a circuit configuration diagram showing a conventional example of a mixer.

[Explanation of symbols]

1 semi-insulating GaAs substrate 2 buffer layer 3 operating layer 4 source 5 gate 6 drain 7 p ⁻ layer 8 p ⁺⁺ layer 9 InGaAs layer 10 electrode 11 hole 12 extraction electrode 50 first bandpass filter 51 1st Impedance matching circuit 52 Second bandpass filter 53 Second impedance matching circuit 56 Third bandpass filter 57 Third impedance matching circuit 60 PG-FET (GaAs MESF with extraction electrode)
ET) 61 Monolithic IC

─────────────────────────────────────────────────── ─── Continuation of the front page (51) Int.Cl. ⁵ Identification number Internal reference number FI Technical display location // H03K 17/687 (72) Inventor Tsuyoshi Yagihara 2-932 Nakamachi, Musashino City, Tokyo Horizontal Kawa Electric Co., Ltd. (72) Inventor Akira Miura 2-9-32 Nakamachi, Musashino-shi, Tokyo Yokogawa Electric Co., Ltd.

Claims (3)

[Claims] 1. N-type GaAs on a semi-insulating GaAs substrate
A layer is formed, and a drain and a source are formed on the n-type GaAs layer.
Scan, and gate - in MESFET forming the gate electrode, the lower portion of the n-type GaAs layer including the electrode forming portion p ^- a layer, the p ^- said to form a p ⁺⁺ layer in the lower layer p ⁺ A MESFET having an extraction electrode formed on the ⁺ layer. 2. The source and drain of the first and second MESFETs are connected, and the gate of the third MESFET is connected to the connection point.
A drain power source is connected to the drain side of the first FET, a source power source is connected to the source of the second MESFET, and an input terminal is connected to the gate of the first MESFET.
The MESFET according to claim 1 is used as the MESFET in an active probe in which an output terminal is provided on the source of the third MESFET, and the first and third MES are used.
An active probe characterized in that the extraction electrode of the FET is connected to each source, and the extraction electrode of the second MESFET is provided with a voltage correction input terminal. 3. A mixer for inputting and mixing two first and second frequencies, wherein the MESFET according to claim 1 is used as a mixing element, and the first frequency is input to the gate of the MESFET. A mixer characterized in that a second frequency is inputted to an extraction electrode and an output terminal is provided on a drain side.