Wave transmission lines and networks – Long line elements and components – Strip type
Reexamination Certificate
1997-07-10
2001-09-04
Lee, Eddie (Department: 2815)
Wave transmission lines and networks
Long line elements and components
Strip type
C333S246000, C257S275000, C257S276000, C257S664000
Reexamination Certificate
active
06285269
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to high-frequency semiconductor devices. The present invention more particularly relates to a high-frequency field effect transistor (FET) for use in a millimeter-wave or quasi-millimeter-wave circuit module for amplification, oscillation, or modulation.
2. Description of the Related Art
FIG. 1
is a plan view showing a structure of an electrode formed on a semiconductor surface in a currently used conventional high-frequency FET. In this high-frequency FET, three source electrodes
2
extend from a source pad section
1
and two drain electrodes
4
extending from a drain pad section
3
are disposed between the source electrodes
2
. Four very narrow gate electrodes
6
extending from two gate pad sections
5
disposed between the tips of the drain electrodes
4
and the source pad section
1
extend the length of areas sandwiched by the source electrodes
2
and the drain electrodes
4
. In other words, this high-frequency FET is a horizontal-type (plane-type) FET in which the source electrodes
2
, the gate electrodes
6
, and the drain electrodes
4
are formed on the same plane.
To make such an FET usable at higher frequencies, it is necessary to reduce the distance between the source electrode and the drain electrode and to narrow the gate electrode (reduce the gate length). A narrow and long gate electrode has large parasitic resistance and parasitic capacitance, however, and thereby the characteristics of the FET deteriorate, including for example a noise increase, an operating-frequency decrease, a gain reduction, and an increased input/output reflection loss.
When the FET is viewed as a waveguide which transmits a microwave, it has a very unusual structure and its operating range is limited to a low frequency zone in which the FET can be approximated to a lumped-constant circuit device.
FIG. 2
is a plan view illustrating an electrode structure of an air-bridge-gate-structure FET which improves upon the above FET of FIG.
1
and has less characteristics deterioration. In this structure, a source electrode
8
disposed between source pad sections
7
on a semiconductor surface faces a drain electrode
9
along its full length. A wide gate electrode
11
extends over the source electrode
8
, a gate pad section
10
is disposed at the side of the gate electrode opposite the drain electrode
9
against the source electrode
8
, and the distal edge of the gate electrode
11
is Schottky-connected to the semiconductor surface between the source electrode
8
and the drain electrode
9
.
Since the gate electrode
11
can be made wide in such an air-bridge-gate-structure FET, the parasitic resistance and the parasitic inductance of the gate electrode
11
are reduced and the RF characteristics (especially noise characteristics) are improved.
At a portion where the gate electrode
11
passes over the source electrode
8
, a parasitic capacitor is generated between the source electrode
8
and the gate electrode
11
, which decreases the operating frequency. To reduce this parasitic capacitance, the source electrode
8
needs to be narrowed. If the source electrode
8
is narrowed, the source electrode
8
gains additional parasitic resistance and additional parasitic inductance, so only a limited amount of characteristics improvement is available in such a method.
When this air-bridge-gate-structure FET is viewed as a waveguide, it has a very unusual structure, like a horizontal-type FET, and its operating range is limited to a low frequency zone in which the FET can be approximated to a lumped-constant circuit device.
To solve the problem of characteristics deterioration in a high-frequency FET for use in millimeter-wave and quasi-millimeter-wave ranges, it is an important issue to eliminate wiring resistors and parasitic components such as parasitic capacitors and parasitic inductors in the gate electrode and the drain electrode, as described above. It is very difficult, however, to suppress characteristics deterioration in a high-frequency range in a conventional FET structure, and a semiconductor device suited to a millimeter wave and a quasi-millimeter wave has not yet been manufactured.
SUMMARY OF THE INVENTION
The present invention is made in consideration of the above-described drawbacks in a conventional device. The present invention is able to suppress characteristics deterioration of a semiconductor device in a high-frequency range by using the structure of a micro-wave transmission line for electrode structures between the gate electrode and the source electrode and between the drain electrode and the source electrode.
According to one aspect of the invention, a high-frequency semiconductor device has an intrinsic device section formed on part of a semiconductor substrate; a source electrode and a drain electrode are disposed in the intrinsic device section with a gate electrode placed therebetween; a micro-wave transmission line is formed between the gate electrode (or an electrode section electrically connected to the gate electrode) and the source electrode (or an electrode section electrically connected to the source electrode); and a micro-wave transmission line is formed between the drain electrode (or an electrode section electrically connected to the drain electrode) and the source electrode (or an electrode section electrically connected to the source electrode).
In such a high-frequency semiconductor device, since a micro-wave transmission line is formed between the drain electrode or an electrode section electrically connected to the drain electrode and the source electrode or an electrode section electrically connected to the source electrode, and a micro-wave transmission line is formed between the gate electrode or an electrode section electrically connected to the gate electrode and the source electrode or an electrode section electrically connected to the source electrode, parasitic components between the gate and source electrodes and between the drain and source electrodes can be reduced and the characteristics of the high-frequency semiconductor device can be improved.
According to another aspect of the invention, a high-frequency semiconductor device has an intrinsic device section formed on part of a semiconductor substrate; a source electrode and a drain electrode are disposed in the intrinsic device section with a gate electrode placed therebetween; the source electrode (or an electrode section electrically connected to the source electrode) covers most or substantial parts of the semiconductor substrate; a micro-wave transmission line is formed by oppositely disposing the gate electrode or an electrode section electrically connected to the gate electrode through a dielectric layer above the source electrode or an electrode section electrically connected to the source electrode; and a micro-wave transmission line is formed by oppositely disposing the drain electrode or an electrode section electrically connected to the drain electrode through a dielectric layer above the source electrode or an electrode section electrically connected to the source electrode.
Any type of micro-wave transmission line can be used, such as a microstripline, a slot line, and a coplanar line. In the high-frequency semiconductor device described above, the source electrode opposes the drain electrode with the dielectric layer disposed therebetween, or the source electrode opposes the gate electrode with the dielectric layer disposed therebetween to form a micro-wave transmission line similar to a microstripline.
The high-frequency semiconductor devices described above may be configured with a plurality of the intrinsic device sections disposed on the semiconductor substrate and with the plurality of the intrinsic device sections being connected by micro-wave transmission lines.
In such a high-frequency semiconductor device, since a plurality of intrinsic device sections are connected with micro-wave transmission lines, a larger output power is obtained than in a single intrinsic
Ishikawa Yohei
Kajikawa Takehisa
Sakamoto Koichi
Yamashita Sadao
Baumeister Bradley William
Lee Eddie
Murata Manufacturing Co. Ltd.
Ostrolenk Faber Gerb & Soffen, LLP
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