JPH0352301A - Switch for microwave - Google Patents

Abstract

PURPOSE:To suppress the insertion loss and to improve the isolation characteristic by connecting two field effect transistors(TRs) in parallel between the inputs and between outputs, coupling them with an inductive transmission line with a prescribed impedance and specifying the impurity concentration to the channel region of the field effect TRs. CONSTITUTION:Field effect TRs 1, 2 are connected in parallel between inputs and between outputs respectively, they are coupled with an inductive transmission line 3 with a prescribed impedance and the impurity concentration of the channel region of the field effect TRs is selected to be 2.0X10<18>/cm<2> or over. A negative gate bias over the pinch-off voltage is applied to the FETs 1, 2 to turn on the FETs, then the capacitance of the FETs 1, 2 and the inductance of a strip line 3 form a kind of low pass filter. On the other hand, since the strip line 3 reaches a high impedance, when the FETs 1, 2 are turned off without applying the gate bias to them, the isolation is improved. Thus, the insertion loss is suppressed and the isolation is also improved.

Description

[Detailed Description of the Invention] [Summary] Regarding microwave switches, especially switches used for switching between transmission and reception in the microwave band, phased array systems, etc., both insertion and isolation require high frequencies. With the aim of achieving excellent characteristics up to
Two transistors are connected in parallel between input and output, and the two transistors are coupled by an inductive transmission line having a predetermined impedance, and the impurity concentration of the channel region of the field effect transistor is 2. OX
IO”/cn! or more.

[Industrial application field]

The present invention relates to a microwave switch, and in particular, to switching between transmission and reception in the microwave band, phased
It relates to switches used in array systems, etc.

In recent years, communication technology has continued to develop at a remarkable pace, and the use of high frequency microwaves is being actively promoted. Microwave switches, which occupy an important position among the devices used in such microwave application equipment, have been developed with the development of communication technology to have low insertion loss and insulation between input and output (
high isolation) is required.

[Prior art and problems to be solved by the invention]

Conventional field effect transistors (FETs) have been developed primarily for use as amplification elements, and therefore are generally designed to have high channel resistance. Therefore, the F
ET poses the following problems when used as a switching element.

For example, as shown in FIG. 6(a), when FETΩ is connected in series (as a series type), the FET
The problem arises of increased power consumption or insertion loss due to the high resistance of the ET channel. In addition, when FETQz is connected in parallel (as a shunt type) as shown in the same figure (b), when the FET is turned on, due to the high resistance of the channel, a A problem arises in that a sufficient amount of current does not flow in, and a portion of the current flows toward the output terminal OUT, resulting in a reduction in isolation between input and output.

To deal with this, if the structure of the FET is devised to reduce the channel resistance, it becomes easier for the current to flow between the source and drain of the FET. In this case, the isolation deteriorates, and in the form (b), the power consumption (insertion loss) in the FET increases.

The present invention was created in view of the problems in the prior art, and an object of the present invention is to provide a microwave switch that achieves excellent characteristics in both insertion loss and isolation up to high frequencies.

[Means to solve the problem]

The microwave switch according to the present invention includes two field effect transistors, the two transistors are connected in parallel between the input and the output, and the gap between the two transistors is inductive and has a predetermined impedance. The impurity concentration of the channel region of the field effect transistor is 2.
It is characterized by being 0x101ll/c or more.

[Function] According to the configuration described above, when the two FETs are in the on state,
The capacitance of the B FET and the inductance of the inductive transmission line act as a kind of low-pass filter, thereby minimizing insertion loss up to high frequencies.

On the other hand, transmission lines have high impedance, so
Isolation can be increased when the two FETs are in the off state. Furthermore, since the channel resistances of the two FETs are low, the FET portions are almost in a short-circuit state when they are in the on state. Therefore, the reflection coefficient of microwaves becomes high, and isolation is further improved.

Note that other structural features and details of the operation of the present invention will be explained using the embodiments described below with reference to the accompanying drawings.

〔Example〕

FIG. 1 shows the circuit structure of a microwave switch as an embodiment of the present invention.

In the same figure, 1, 2 and 4 are gallium arsenide (Ga
As) FET, 3 indicates a transmission line with high impedance, and in this example, the transmission line 3 is a strip
It consists of a amplifier line, one end of which is connected to the input end IN via the FET 4, and the other end connected to the output end OUT. Further, FETI is connected between one end of the strip line 3 and ground, and FET 2 is connected between the other end of the strip line 3 and ground. That is, FETI
and FET2 are connected in parallel to the signal line, and the strip line 3 is connected in series to the signal line.

FETI and FET2 each receive a gate signal G. G
z, FET4 responds to gate signal G0.

In this embodiment, each gate signal G o , G
．． G t is applied. An example of application timing is shown in FIG.

FIG. 3 shows the structure of the FET in FIG. 1 in cross section.

In the figure, IO is a semi-insulating GaAs substrate, 11.12 is a diffusion layer of high concentration (n゛) impurity, such as silicon (Si), 13 is a channel layer (active layer), and 14.15 is a diffusion layer. For example, gold/germanium/nickel/gold (AuGe/Ni/A
u), and l6 is made of, for example, gold (A
u) or a gate electrode made of aluminum (AI).

When the impurity concentration in the channel (layer) is N and the thickness of the channel is a, the resistance R of the channel is inversely proportional to N and a as shown in the following equation.

Ra: l/Na Therefore, if the dose is increased, N will increase and R will become smaller, and if the implantation energy is increased, a will be deposited and R will also become smaller.

FIG. 4 shows the relationship between the dose amount, injection artificial inertia, and channel resistance.

Referring to the figure, if the implantation energy is the same, as the dose increases, the channel resistance decreases;
It will be understood that if the dose is the same, the channel resistance will be lower as the implantation energy is greater.

For the FET to be suitable for use as a switching element, the channel resistance must be approximately 2.5 Ω or less per 1 mm+ gate width. Therefore, the impurity concentration in the channel layer l3 is 2. Must be OX10"/CT1 or higher.

Therefore, in this embodiment, in the step of forming the channel layer 13 directly under the gate electrode l6, the dose of Si ions is set to 3.5×10Iff/CTII or more, and the implantation energy is set to 100KeV or more.

Although the channel resistance of an FET controlled under such setting conditions will certainly be lower, on the other hand, the capacitance of the FET will increase, and as the frequency increases, its characteristics as a switching element will deteriorate. It's about the same time as F.

In contrast, in this embodiment, the transmission line 3 is formed of a high impedance strip line, so the line is inductive.

Therefore, apply a negative gate bias to FETI and 2 above its pinch-off voltage (-5V in this example).
When the FET is turned on, the capacitance of the FET I2 and the inductance of the strip line 3 are
As shown in the figure, it constitutes a kind of low-pass filter. This makes it possible to minimize insertion loss up to high frequencies.

On the other hand, since the strip line 3 has a high impedance, it contributes to improving isolation when the FETs are turned off without applying gate bias to the FETs I and 2. Furthermore, since the resistance of the channel of FETI, 2 is very small as mentioned above, when the FET is turned on, the gK FET is almost in a short-circuit state, which increases the reflection coefficient of the microwave and makes it even more isolating. ration is improved.

Note that the FET 4 connected in series with the signal line functions to cant the direct current from the input terminal IN.

〔Effect of the invention〕

As explained above, according to the microwave switch of the present invention, insertion loss can be suppressed and isolation can be improved.

[Brief explanation of drawings]

Fig. 1 is a circuit diagram showing the configuration of a microwave switch as an embodiment of the present invention, Fig. 2 is a timing diagram for applying each gate signal, and Fig. 3 shows the structure of the FET in Fig. 1. 4 is a diagram showing the relationship between dose amount, implantation energy, and channel resistance. FIG. 5 is an equivalent circuit diagram of the main part of the switch in FIG. 1. FIG. 6 (a) and (b) 1 is a diagram showing an example of the configuration of a conventional microwave switch. (Explanation of symbols) l, 2, 4...field effect transistor (FET), 3
...Transmission line (strip line), 13...Channel layer (active layer), IN...Manual power end, OUT...Output end.

Claims (1)

[Claims] Two field effect transistors (1, 2) are provided, the two transistors are connected in parallel between input and output (IN, OUT), and the space between the two transistors is inductive and are coupled by a transmission line (3) having a predetermined impedance,
2. The microwave switch according to claim 1, wherein the impurity concentration of the channel region of the field effect transistor is 2.0×10^1^8/cm^3 or more.