Active solid-state devices (e.g. – transistors – solid-state diode – Field effect device – Having insulated electrode
Reexamination Certificate
2001-07-20
2003-10-21
Tran, Minh Loan (Department: 2826)
Active solid-state devices (e.g., transistors, solid-state diode
Field effect device
Having insulated electrode
C257S133000, C257S135000, C257S341000
Reexamination Certificate
active
06635926
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a field effect transistor, and more particularly, it relates to a field effect transistor with a high withstand voltage and a low resistance.
2. Description of the Related Art
Conventionally, a field effect transistor in which a current flows in the direction of the thickness of a substrate has been used as a current control element.
Referring now to
FIG. 26
, a reference numeral
105
denotes one example of a conventional type of a field effect transistor, and it has a single crystal silicon substrate
111
. On the surface of the single crystal substrate
111
, a drain region
112
formed by epitaxial growth is disposed.
Within the single crystal silicon substrate
111
, N-type impurities are doped to a high concentration and a drain electrode film
148
is formed on the backside thereof. Within the drain region
112
, N-type impurities are doped to a low concentration, and a P-type base region
154
is formed in the vicinity of the surface thereof.
Within the base region
154
, N-type impurities are further diffused from the surface to form a source region
161
.
A reference numeral
110
denotes a channel region located between the edge portion of the source region
161
and the edge portion of the base region
154
. On tip of the channel region
110
, a gate insulation film
126
and a gate electrode film
127
are disposed in this order.
On the surface and the sides of the gate electrode film
127
, an interlayer insulation film
141
is formed, and a source electrode film
144
is formed on the surface thereof.
The base regions
154
as described above are disposed in islands in the vicinity of the surface of the drain region
112
, and one base region
154
, and the source region
161
and the channel region
110
disposed within the base region
154
form one cell
101
.
FIG. 27
is a plan view showing the surface of the drain region
112
, wherein a plurality of rectangular cells
101
are arranged in matrix.
In the case where the field effect transistor
105
is used, when the source electrode film
144
is set at a ground potential, a positive voltage is applied to the drain electrode film
148
, and a gate voltage (positive voltage) of equal to or greater than the threshold voltage is applied to the gate electrode film
127
, an N-type inversion layer is formed on the surface of the P-type channel region
110
so that the source region
161
and the drain region
112
are connected to each other through the inversion layer, thereby rendering the field effect transistor
105
conductive.
When a voltage of equal to or smaller than the threshold voltage (e.g., ground voltage) is applied to the gate electrode film
127
from such a state, the inversion layer disappears so that the field effect transistor
105
is cut off.
However, when a large number of the cells
101
as described above are arranged, an attempt to increase the withstand voltage requires a decrease in the distance between the cells
101
, and hence the gate electrode width is decreased, thereby resulting in an increase in conduction resistance.
Further, the withstand voltage is determined by the corner portion of the cell
101
, and hence there is still a problem in that even if the distance between the cells
101
is decreased, the withstand voltage is not so improved as expected.
SUMMARY OF THE INVENTION
The present invention has been made in order to solve the foregoing deficiencies in the prior art. It is therefore an object of the present invention to provide a high withstand voltage and low resistance field effect transistor.
For solving the foregoing problem, a first aspect of the present invention is a field effect transistor, comprising: a main diffused region of a second conductivity type formed within a high resistance layer of a first conductivity type, and disposed on the surface side of the high resistance layer; a source region of the first conductivity type formed within the main diffused region, and disposed on the surface thereof; a ring-shaped channel region being formed in a ring, being a part of the main diffused region, and located between the edge of the main diffused region and the edge of the source region; a drain region surrounded by the ring-shaped channel region; a gate insulation film disposed at least on the channel region surface; and a gate electrode film disposed on the gate insulation film surface, the source region is located at an outer periphery of the ring-shaped channel region, the source region and the high resistance region being electrically connected with each other upon inversion of the channel region surface into the first conductivity type due to a voltage applied to the gate electrode film.
A second aspect of the present invention is the field effect transistor in accordance with the first aspect of the present invention, wherein the drain region surrounded by the ring-shaped channel region has at least one narrow elongate body portion, and a plurality of branch portions with their respective one ends connected to the body portion, and the ring-shaped channel region is disposed so as to surround the periphery of the body portion and the branch portions.
A third aspect of the present invention is the field effect transistor in accordance with the second aspect of the present invention, wherein the body portion located between the branch portions extends roundly toward the inside of the body portion itself.
A fourth aspect of the present invention is the field effect transistor in accordance with the third aspect of the present invention, wherein the channel region at each tip of the branch portions is configured with three sides intersecting with each other at substantially right angles.
A fifth aspect of the present invention is the field effect transistor in accordance with the third aspect of the present invention, wherein the main diffused region comprises a P-type base region and a P-type ohmic region having a deeper diffusion depth than that of the base region, a conductive layer of the first conductivity type with a lower resistance than that of the high resistance layer is disposed in the vicinity of the surface inside of the drain region, a pn junction is formed with the ohmic region and the conductive region at least on the surface of the tip portion of the portion extending roundly toward the inside of the body portion.
A sixth aspect of the present invention is the field effect transistor in accordance with the second aspects of the present invention, wherein a conductive layer of the first conductivity type with a lower resistance than that of the high resistance layer is disposed on the surface side of the inside of the drain region.
A seventh aspect of the present invention is the field effect transistor in accordance with the third aspect of the present invention, wherein a conductive layer of the first conductivity type with a lower resistance than that of the high resistance layer is disposed in each of the branch portions.
An eighth aspect of the present invention is the field effect transistor in accordance with the second aspect of the present invention, wherein a floating potential region of the second conductivity type not in contact with the channel region is disposed on the surface side of the inside of the drain region.
A ninth aspect of the present invention is the field effect transistor in accordance with the first aspect of the present invention, wherein the high resistance layer is disposed on a low resistance layer of the first conductivity type with a lower resistance than that of the high resistance layer, and a drain electrode film for forming an ohmic junction with the low resistance layer is disposed on the back side of the low resistance layer.
A tenth aspect of the present invention is the field effect transistor in accordance with the first aspect of the present invention, wherein an anode electrode film for forming a Schottky junction with the high resistance layer is disposed on the back side of the high resistance layer, such
Matsubara Toshiki
Miyakoshi Nobuki
Nakamura Hideyuki
Dickey Thomas L
Shindengen Electric Manufacturing Co. Ltd.
Tran Minh Loan
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