Active solid-state devices (e.g. – transistors – solid-state diode – Housing or package – Insulating material
Reexamination Certificate
1998-09-11
2001-11-13
Williams, Alexander O. (Department: 2826)
Active solid-state devices (e.g., transistors, solid-state diode
Housing or package
Insulating material
C257S276000, C257S341000, C257S275000, C257S277000, C257S287000, C257S712000, C257S469000, C257S579000, C257S583000, C257S563000, C257S280000
Reexamination Certificate
active
06316827
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a semiconductor device, and more particularly to reliability of a semiconductor transistor against heat.
2. The Related Art
Semiconductor transistors are used as amplifiers for mobile communication and satellite communication. Demands for higher power are increasing with regard to these semiconductor transistors. However, higher power is accompanied by increased heat generation, which can adversely influence the life of the semiconductor transistor. Some of the adverse influences that result from an increase in heat generation affect the characteristics of the semiconductor transistor and result in, for example, decreased drain current and increased gate leakage current. These not only can cause degradation in the characteristics at high temperature, but sometimes cause irreversible degradation. As a result, the device characteristics do not return to normal after the temperature falls, and may even result in massive failure or breakage. Accordingly, in making such a high power semiconductor transistor device, a technique is needed to maintain its characteristics against heat degradation.
One means for preventing transistor heat degradation is introduced in Japanese Patent Application Laid-open No. Sho 61-23350.
FIG. 14
shows a sectional view of a semiconductor device (an FET substrate) described in the application No. Sho 61-23350. A cavity is provided in the rear surface of a semiconductor substrate
101
. Heat generating region (active region or element formation region)
103
is formed on the front surface of the semiconductor substrate
101
and gold-plate electrode for heat radiation
102
is formed on the back surface of the semiconductor substrate
101
. By making the thickness of the substrate right below the heat generating region
103
, the heat radiation of the region small (thin) is enhanced.
Japanese Patent Application Laid-open No. Sho 56-131936 also proposes such a semiconductor device.
FIG. 15
shows a sectional view of a semiconductor integrated circuit device described in the Application No. Sho 56-131936. A plurality of heat generating region
203
are formed on a front surface of a semiconductor substrate
201
. The heat generating regions
203
are surrounded by non-generating heat regions
204
. Gaps
205
are formed on a back surface of the semiconductor substrate
201
so as to oppose the respective heat generating regions
203
.
However, the inventor has determined that a heat generating region of the semiconductor device has a temperature distribution depending on its shape. That is, temperature produced at a central portion of the heat generating region is high compared with temperature produced at a peripheral portion of the heat generating region. Thus, the conventional devices have the problem that device characteristics deterioration occurs at the center portion of the heat generating regions (localized hot spots) of the device due to uneven distribution in the heat generating region and concentration of the heat at the center of the heat generating portion of the device.
SUMMARY OF THE INVENTION
One object of the present invention is to provide a semiconductor device which has uniform temperature distribution throughout a heat generating region of a semiconductor device so as to reduce or eliminate localized hot spots.
A semiconductor device according to the present invention is characterized that the shape of plate electrodes, which are formed over source plate electrode or drain plate electrodes of a transistor, or the shape of the rear surface substrate in a heat generating region is formed differently with regard to the center portion and a peripheral portion of the heat generating region.
More specifically, a plate electrode located around the center portion of the heat generating region has a width larger than the width of a plate electrode located around a peripheral portion of the heat generating region.
Further, the plate electrodes are formed so as to be perpendicular to at least one of the drain and source plate electrodes, and the density of the plate electrodes is dense around the center portion of the heat generating region and is sparse at a peripheral portion of the heat generating region.
Still further, the thickness of a substrate at the rear surface of the heat generating portion is thin at the center portion of the heat generating region, and is thick at a peripheral portion of the heat generating region.
Paths of dissipation of generated heat are dissipation from an upper portion of a heat generating region into the air and dissipation from the rear surface of a heat generating region to a seating. By processing plate electrodes or the rear surface substrate in a heat generating region, the heat radiation of the center portion of the heat generating region is enhanced compared with that of a peripheral portion of the heat generating region. Thus, the temperature distribution of heat in the generating region is substantially even and localized hot spots are reduced or eliminated. Accordingly, heat at the center portion of the heat generating region is suppressed and temperature of the respective portions of the heat generating region approaches the average temperature of the entire region, which reduces the adverse effects of heat on the characteristics of the semiconductor transistor.
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Asano Kazunori
Ishikura Kouji
NEC Corporation
Sughrue Mion Zinn Macpeak & Seas, PLLC
Williams Alexander O.
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