Semiconductor device manufacturing: process – Formation of electrically isolated lateral semiconductive... – Total dielectric isolation
Reexamination Certificate
2000-03-31
2003-02-04
Whitehead, Jr., Carl (Department: 2822)
Semiconductor device manufacturing: process
Formation of electrically isolated lateral semiconductive...
Total dielectric isolation
C438S380000, C438S718000
Reexamination Certificate
active
06514832
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to Gunn diodes used for oscillation of microwaves and millimeter waves, and is especially related to Gunn diodes which realize improvements in thermal characteristics, yield factor of good products and easy assembly to planar circuits, fabricating methods thereof and structures for assembly of the same.
The present invention also relates to NRD guide Gunn oscillators that are comprised by combining a NRD guide (Non Radiative Dielectric Waveguide) circuit and Gunn diodes.
Gunn diodes for oscillation of microwaves or millimeter waves are usually comprised of compound semiconductors such as gallium arsenide (GaAs) or indium phosphide. It is the case with such compound semiconductors that the electron mobility is several thousands of cm
2
/V·sec and thus large in a low electric field while the mobility is decreased in case a large electric field is applied since accelerated electrodes transit to a band of large effective mass and thus causes generation of negative differential mobility within the bulk. Consequently, a negative differential conductance is caused in the current-voltage characteristics and leads to thermodynamic instability. Therefore, a domain is generated which transits from the cathode side to the anode side. Repetition of this phenomenon results in vibrating current (oscillation).
The oscillating frequency of a Gunn diode is determined by the distance of transit of the domain. In case of Gunn diodes for millimeter waves, this distance of transit needs to be extremely short (1 to 2 &mgr;m). In addition, the product of an impurity concentration and a distance of transit for the domain (active layer) needs to be set to be a specified value (e.g. 1×10
12
/cm
2
) to obtain sufficient oscillating efficiency, while the impurity concentration of the active layer becomes rather high in high frequency zones like those of millimeter waves since the oscillating frequency is non-ambiguously determined by the thickness of the active layer. The current concentration during operation is determined by the product of the impurity concentration of the active layer and a saturation electron speed, and in zones of the millimeter waves, the temperature of the active layer is increased owing to the increase in current concentration, whereby the oscillating efficiency is decreased.
In order to solve such problems, measures had been taken with conventional Gunn diodes for millimeter waves such as employing a mesa-type arrangement to use elements including the active layer of extremely small sizes, having diameters of approximately several tens of &mgr;m, and assembling the diodes within pill-type packages comprised with a heat portion made of diamond or similar material of favorable thermal conductivity which greatly affects oscillating efficiency on which the most important performance indices are dependent.
A sectional view of gallium arsenide Gunn diode element
100
of conventional mesa-type arrangement is shown in FIG.
29
.
On to a semiconductor substrate
101
of high concentration n-type gallium arsenide, there are sequentially laminated, through MBE method, a first contact layer
102
of high concentration n-type gallium arsenide, an active layer
103
of low concentration n-type gallium arsenide, and a second contact layer
104
of high concentration n-type gallium arsenide, and it is employed a mesa-type arrangement in order to reduce the transit space for the electrons.
Thereafter, a rear surface of the semiconductor substrate
101
is laminated, a cathode electrode
105
is formed onto this rear surface of the semiconductor substrate
101
while an anode electrode
106
is formed on the surface of the second contact layer
104
, and by performing element separation, the Gunn diode element is completed.
The Gunn diode element
100
thus obtained is built-in in a pill-type package
110
as shown in FIG.
30
. This pill-type package
110
comprises a heat sink electrode
111
and a cylinder
112
of glass or ceramics that serves as an enclosure for enclosing the Gunn diode element
100
, wherein the cylinder
112
is brazed by hard-soldering to the heat sink electrode
111
. The Gunn diode element
100
is electro-statically attracted by a bonding tool of sapphire material or the like (not shown) and is adhered to the heat sink electrode
111
.
Further, the Gunn diode element
100
and a metal layer provided at a tip of the cylinder
112
are connected by a gold ribbon
113
through thermo-compression bonding or the like. After connecting the gold ribbon
113
, a lid-like metallic disk
114
is brazed onto the cylinder
112
to complete the building-in to the pill-type package
110
.
An example of a structure for assembling the Gunn diode that has been built-in in the pill-type package
110
to a microstrip line
120
is shown in FIG.
31
. One of the two electrodes
111
,
114
of the pill-type package
110
is pierced through a hole formed in a flat insulating substrate
121
of e.g. alumina and is electrically connected to a ground electrode
122
formed on a rear surface of the flat insulating substrate
121
, while the other one is connected by a gold ribbon
123
to a signal line
124
formed on the plate substrate
121
as a microstrip line.
NRD guide circuits are paid attention to as transmission lines for microwaves, especially of millimeter wave zones of not less than 30 GHz, since they present lower insertion losses than compared to microwave strip lines, and since manufacturing of transmission line is easier than compared to waveguides.
This NRD guide circuit is arranged in that a dielectric strip line, in which propagation of electromagnetic waves is performed, is pinched between two parallel plates of conductive metal. Since the opposing distance between the parallel plates is set to be not more than half of the free space wavelength of the used frequency, electromagnetic waves are intercepted and its radiation is restricted at portions other than the dielectric strip line, electromagnetic waves can be propagated with low losses along the dielectric strip line.
Oscillators arranged of such a NRD guide circuit and Gunn diodes of 35 GHz and 60 GHz zone have been developed which are capable of producing output power which are equivalent to those of waveguides.
FIG.
32
(
a
) is a view showing an arrangement of a conventional NRD guide Gunn oscillator. This is arranged in which a mount
320
is provided in a space between parallel plates
201
,
202
, being mounted with a dielectric strip line
203
as well as Gunn diode
310
. High frequency output oscillated by the Gunn diode
310
is derived to the dielectric strip line
203
via a resonator
330
. FIG.
32
(
b
) is a view showing a representative example of such resonator
330
comprised with a copper layer portion
331
patterned through etching a copper layer of a Teflon copper-clad laminate. By adjusting the width or length of the copper layer portion
331
, the output frequency can be adjusted.
FIG. 33
is a view showing the arrangement of the mount
320
. The Gunn diode
310
is set in a cylindrical portion
321
, and bias voltage is applied thereto via a bias choke
340
connected to aside the cylindrical portion
321
. The bias choke
340
is obtained by patterning through etching a Teflon copper-clad laminate and by hacking a portion of the laminated plate of the cylindrical portion
321
such that a copper layer portion remains to be connected to a lid for connecting portion
341
. A cathode electrode of the Gunn diode
310
is connected onto a heat sink
322
of the mount
320
. The heat releasing base
322
is insulated and separated from the lid
341
by a cylindrical ceramic
342
, and the lid
341
is connected to an anode electrode of the Gunn diode
310
via a ribbon
343
.
Conventional Gunn diode elements
100
(
FIG. 30
) are formed through chemical wet etching by employing a photoresist as an etching mask to obtain the above described mesa-type arrangement. However, since etching is progressed not only in the depth direction but al
Nakagawa Atsushi
Watanabe Ken'ichi
Armstrong Westerman & Hattori, LLP
Brophy Jamie L.
Jr. Carl Whitehead
New Japan Radio Co. Ltd.
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