JPS6228788Y2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a junction gate field effect transistor.

Field effect transistors (FETs) for microwave amplification include FETs that use elemental semiconductors such as silicon (Si), and Schottky junction field effect transistors (MESFETs) that use compound semiconductors such as gallium arsenide (GaAs). etc.,
In particular, the latter allows amplification operation in a higher frequency band than the former. GaAs MESFET like this
In order to reduce the series resistance of the gate electrode metal, as shown in FIG. 1, source electrodes 31 and drain electrodes 41 are alternately arranged on the active layer 2, and a gate electrode 51 is arranged between them. There are many. a set of adjacent source electrodes, gate electrodes,
The drain electrode 6 is called a unit element. Each gate electrode is connected to a gate power supply bus 520, and is collectively supplied with a gate bias voltage and an input electrical signal from a gate power supply pad 53. In addition, each drain electrode is connected to the drain power supply bus 42 in the same way as the gate electrode.
0, and the drain bias voltage is often supplied and the output electric signal is taken out all at once from the drain power supply pad 43.

In such a GaAs MESFET, the effective length of the gate power supply path from the gate power supply pad to each gate electrode, or the effective length of the drain power supply path from the drain power supply pad to each drain electrode, differs for each unit element, so that in the microwave band, each unit element cannot operate in a balanced manner with the same phase.
For example, a 20 GHz wave propagating through a 20 μm wide gate power bus formed on a 0.15 mm thick high resistivity GaAs substrate.
One wavelength of the signal is approximately 4.4 mm. If the difference between the effective length from the gate electrode closest to the feed pad to the feed pad and the effective length from the gate electrode furthest from the feed pad to the feed pad is sufficiently small compared to 4.4 mm, there is no problem. However, if the difference is, for example, 2.2 mm, the signals applied to the gate electrode closest to the feed pad and the gate electrode furthest from the feed pad will be in completely opposite phase, and will cancel each other out. Since the phase difference between each unit element increases as the number of unit elements increases or the frequency increases, there are inconveniences such as little increase in output power even if the number of unit elements is increased, or the gain and output power drop significantly as the frequency increases, and there is also the disadvantage that the operation of the MESFET is unstable and prone to self-oscillation.

SUMMARY OF THE INVENTION An object of the present invention is to provide a junction gate field effect transistor that eliminates the above-mentioned conventional drawbacks.

According to the present invention, a plurality of source electrodes and drain electrodes are arranged alternately, a junction gate electrode is provided between the source electrodes and the drain electrodes, and at least one type of electrode of the source electrode, drain electrode, and gate electrode is provided. In contrast, in a junction gate field effect transistor comprising a power supply pad made of a metal film for electrical connection with an external circuit and a power supply bus bar made of a metal film connecting the power supply pad and an electrode, At least one type of feeding bus is derived from a feeding pad and branched into two or more to form a first stage feeding bus, and is derived from an end of the first stage feeding bus and branched into two or more to form a first stage feeding bus. It has a dendritic structure of two or more stages in which the branches forming a two-stage power supply bus are successively repeated, and the difference in the effective length of the power supply path from the power supply pad to each electrode is transmitted through the power supply bus. A junction gate field effect transistor is obtained which is characterized by a wavelength that is practically negligible compared to the wavelength of an electric signal.

The present invention will be explained below with reference to the drawings.

FIG. 2 is a drawing showing an embodiment of the present invention.
In Figure 2, 1 is a high resistance doped with chromium.
The GaAs substrate 2 is an n-type GaAs epitaxial active layer with a carrier density of 1.5×10 ¹⁷ cm ⁻³ and a thickness of about 0.27 μm grown thereon. On this active layer, a source electrode 31 and a drain electrode 41 are formed by laminating gold/germanium alloy, nickel, and gold in this order.
They are formed alternately at intervals of 3 μm, are derived from the power supply pad and branched into two or more to form a first stage power supply bus, and are derived from the terminal end of the first stage power supply bus and branched into two or more. By sequentially repeating the branching to form a second-stage power supply bus, a drain power supply bus 421, 422, 42 having a dendritic structure with two branches and three stages is formed.
3 and drain power supply pad 43 are also formed at the same time. The thickness of the shot junction electrode 51 is 0.6 μm.
An aluminum (Al) film with a thickness of 0.7 μm and a length of 100 μm is used between the source and drain electrodes.
Gate power supply buses 523, 522, which have a dendritic structure with two branches, two stages, and four branches, one stage.
521 and gate feed pad 53 are formed simultaneously. The distance between gate electrodes is 30μm
It is. flip-tip mount
The source electrode 31 is selectively plated with gold to a thickness of 12 μm so that it can be directly grounded by a mount.

By forming the power supply bus into a dendritic structure in this way, there is almost no difference in the effective length of the power supply path from the power supply pad to each electrode, and each unit element can now operate in a balanced manner with the same phase. As a result
MESFET operation has become extremely stable, and matching and bias circuits have become easier to design and adjust. Self-oscillation is also prevented, and self-oscillation
MESFET destruction has also been eliminated, improving reliability. Also, at 18GHz, the gain was improved by 0.5dB and the saturated output power was improved by 0.3dB.

In this example, the case where both the drain power supply bus and the gate power supply bus have a dendritic structure has been described, but it is also possible to create a GaAs
Needless to say, MESFET can be obtained. Note that since the GaAs MESFET according to this example is designed to amplify a signal of 18 GHz, the interval between adjacent gate electrodes was set to 30 μm, and the final stage of the gate power supply bus had four branches. One wavelength of an 18GHz signal is approximately 4.8mm, so the difference in distance between the four gate electrodes that are branched into four is 30μm, which is 1% of the wavelength.
It is sufficiently small as below, and its influence can be ignored in practical terms. Further, if a similar structure is applied to the source electrode, there is an advantage that the ground impedance acting as a feedback element can be made uniform without flip-chip mounting. Also, only the case where n-type GaAs is used is shown, but p-type GaAs or GaAs
Needless to say, the same applies to other compound semiconductors or Si.

[Brief explanation of the drawing]

FIG. 1 is a diagram for explaining a conventional shotgun junction gate field effect transistor, and FIG. 2 is a diagram for explaining an embodiment of the present invention.
In the drawing, 1 is a high resistance semiconductor substrate, 2 is a semiconductor active layer, 31 is a source electrode, 41 is a drain electrode, 420 to 423 are drain power supply buses, 43 is a drain power supply pad, 51 is a gate electrode, 520
523 is a gate power supply bus, 53 is a gate power supply pad, and 6 is a unit element.

Claims (1)

[Scope of utility model registration request] A plurality of source electrodes and drain electrodes are arranged alternately, a junction gate electrode is provided between the source electrodes and the drain electrodes, and an external In a junction gate field effect transistor comprising a power supply pad made of a metal film for electrical connection with a circuit, and a power supply bus bar made of a metal film connecting the power supply pad and an electrode, at least One type is derived from a power supply pad and branches into two or more to form a first stage power supply bus, and one type is derived from the end of the first stage power supply and branched into two or more to form a second stage power supply bus. It has a dendritic structure of two or more stages in which the forming branches are sequentially repeated, and the difference in the effective length of the power supply path from the power supply pad to each electrode corresponds to the wavelength of the electrical signal transmitted through the power supply bus. A junction gate field effect transistor is characterized by being so small that it can be ignored in practical terms.