Active solid-state devices (e.g. – transistors – solid-state diode – Integrated circuit structure with electrically isolated... – Lateral bipolar transistor structure
Reexamination Certificate
2001-06-05
2004-01-06
Jackson, Jerome (Department: 2815)
Active solid-state devices (e.g., transistors, solid-state diode
Integrated circuit structure with electrically isolated...
Lateral bipolar transistor structure
C257S561000, C257S562000, C257S563000, C257S565000, C257S579000
Reexamination Certificate
active
06674147
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to a semiconductor device having a bipolar transistor structure which has a fast switching speed and can reduce power consumption. More specifically, the present invention relates to a semiconductor device having a bipolar transistor which contains a Zener diode at its base, can be used as a digital transistor, or makes it possible to provide a fast switching with low power consumption, while providing a large current capability, with a structure of stripe emitters, multi-emitters or multi-bases.
BACKGROUND OF THE INVENTION
The principled structure of bipolar transistors heretofore used is the one shown in FIG.
13
. That is, formed in the surface layer portion of an n-type semiconductor layer
11
, is a p-type base region
12
, within which an n-type emitter region
13
is formed. Joined to the base region
12
is a base electrode
16
through a contact region
15
consisting of p
+
-type region, and joined to the emitter region
13
is an emitter electrode
17
. A collector electrode
18
is provided on the back of an n
+
-type semiconductor substrate
11
a
under the n-type semiconductor layer
11
. Numeral
19
designates an insulation film.
A bipolar transistor Tr with this structure, when used as a switching circuit, for example, shown in
FIG. 14
(a), is connected though a resistor R
1
to a power voltage V
CC
, wherein when a signal is inputted into the base, a base current I
B
flows, and thus the transistor Tr is operated to cause a collector current I
C
to flow. When considering a backward withstand voltage of the transistor, a backward withstand voltage BV
CEO
between collector/emitter with the base opened should be larger than the power voltage V
CC
, and a backward withstand voltage BV
CBO
between collector/base with the base opened has been known to generally have a relationship with the BV
CEO
of the following equation (1), because a somewhat current flows even with the base opened, and thus a current amplification factor h
FE
is effective. FIG.
14
(
b
) is a circuit diagram of an example consisting of a digital transistor described later.
V
CC
<BV
CEO
=BV
CBO
/(1+
h
FE
)
1
(1)
For example, trying to use the backward withstand voltage BV
CEO
between collector/emitter at 24 V, a design must be made so that the backward withstand voltage BV
CBO
between collector/base exhibits 60 V. To make this backward withstand voltage BV between collector/base higher, it is necessary to make the impurity concentration of the semiconductor layer
11
lower with a structure shown in the above-mentioned
FIG. 13
, and make larger the thickness d of the n-type semiconductor layer
11
located on the lower side of the base region
12
so that a depletion layer is sufficiently widened. Making lower the impurity concentration of the n-type semiconductor layer
11
or making thicker the thickness d thereof causes the series resistance between emitter/collector to be increased. On the other hand, a voltage V
CE(sat)
between collector/emitter when the transistor is allowed to operate to reach a steady state becomes larger in proportion to the BV
CEO
, that is the BV
CBO
as shown in the following equation (2), so that trying to make larger the backward withstand voltage BV
CBO
between collector/base causes also the V
CE(sat)
to become larger.
V
CE(sat)
∝BV
CEO
=BV
CBO
/(1
+h
FE
)
1
(2)
On the other hand, the power consumption becomes a product of the voltage V
CE(sat)
between collector/emitter in a steady state by the collector current I
C
, so that the power consumption becomes larger by that portion if the withstand voltage BV
CBO
between collector/base is made larger.
In transistors requiring a large current, since the collector current relates mainly to the area and peripheral length of the emitter, so that a transistor structure can be assumed in which the area and peripheral length of the emitter are made large and which has multi-emitters, multi-bases or stripe emitters reducing the current density, but such structure not so contribute to the improvement in switching speed or the reduction in power consumption.
Further, where a voltage-drive type transistor such as a digital transistor is configured using such a bipolar transistor, for example, as shown in FIG.
14
(
b
), the voltage-drive type transistor is formed of a circuit in which when a predetermined voltage is applied through dividing resistances R
1
, R
2
to the base B of a bipolar transistor Q, the transistor Q is turned on, while when a predetermined voltage is not obtained, the transistor Q is not turned on. However, the bias setting by such dividing resistances provides a problem in that the speed is delayed due to the load capacity of the resistances and the like. Also, even when connecting a Zener diode externally to the base of the transistor, a capacity develops due to connecting lead and the like, thereby causing speed to become lower.
As described above, a bipolar transistor of this type has a problem in that trying to improve the backward withstand voltage causes the operating voltage (V
CE(sat)
) to be also raised, thereby making power consumption large.
Further, although, in the above-mentioned transistor structure, the connecting portion of the base region with the base electrode
16
is formed with the p
+
-type contact region
15
in order to obtain an ohmic contact by increasing impurity concentration, a higher impurity concentration in the contact region
15
causes electrons of a few number carriers to be blocked by the p/p
+
junction between the base region
12
and the contact region
15
, whereby at switching operation, an electron accumulation develops in the base region
12
. This provides a problem in that the switching loss becomes large, thereby preventing a fast switching (in particular, making off time longer), and further increasing power consumption.
Voltage-drive type transistors such as digital transistors using conventional bipolar transistors have a problem in that bias setting is made by resistance dividing, so that the load capacity becomes large and thus the speed is lowered.
SUMMARY OF THE INVENTION
The present invention is made to solve such problem, and an object of the present invention is to provide a semiconductor device having a bipolar transistor which has a high withstand voltage and can reduce power consumption.
Another object of the present invention is to provide a semiconductor device having a transistor which can obtain the fast switching speed and the large current.
Still another object of the present invention is to provide a voltage-drive type bipolar transistor, such as a digital transistor, which has a small load capacity while setting (establishing) a disired drive voltage.
Yet another object of the present invention is to configure a circuit using a Zener diode and a transistor for protecting against overvoltage and the like, by a discrete package containing two normal elements.
A semiconductor device according to the present invention has a bipolar transistor structure including; a first conductivity type semiconductor layer taken as a collector region, a base region consisting of a second conductivity type region provided in said first conductivity type semiconductor layer, an emitter region consisting of a first conductivity type region provided in said base region, a base electrode connecting portion having a first conductivity type provided in said base region, a base electrode provided on the surface of said base electrode connecting portion, and an emitter electrode and a collector electrode provided and electrically connected to said emitter region and said collector region, respectively.
With this structure, the semiconductor region is formed which conductivity type is different from that of the base region, between the base electrode and the base region, so that as a semiconductor structure, the structure between collector/base and that between collector/emitter become substantially the same. And since a
Arent Fox Kintner & Plotkin & Kahn, PLLC
Fenty Jesse A.
Jackson Jerome
Rohm & Co., Ltd.
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