Active solid-state devices (e.g. – transistors – solid-state diode – Responsive to non-electrical signal – Temperature
Reexamination Certificate
2001-09-26
2002-11-26
Tran, Minh Loan (Department: 2826)
Active solid-state devices (e.g., transistors, solid-state diode
Responsive to non-electrical signal
Temperature
C257S401000, C257S342000, C257S341000, C257S343000, C257S532000
Reexamination Certificate
active
06486523
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention generally relates to a power semiconductor device and, more particularly, to the power semiconductor device having at least one temperature detector incorporated therein.
2. Description of the Prior Art
The power semiconductor device is generally known as used to deal with a relatively high electric power and does therefore evolve a relatively large amount of heat. In order to protect the power semiconductor device from being overheated, importance has come to be recognized to provide the semiconductor device with an overheat protection. For this purpose, the power semiconductor is generally provided with a temperature detector on the same substrate where semiconductor elements are formed, to thereby monitor the temperature of the substrate. The prior art power semiconductor device having such a temperature detector incorporated therein will be discussed in detail with particular reference to
FIGS. 11 and 12
.
As shown in
FIG. 11
, the power semiconductor device identified by
50
includes a power semiconductor element
80
such as, for example, an insulated gate bipolar transistor (IGBT) and a temperature detector
60
. This temperature detector
60
employed in the power semiconductor device
50
is made up of two diode elements
70
and
71
formed on a p-type region
52
of the substrate
51
with a insulating layer
54
intervening therebetween. As shown in an equivalent circuit diagram in
FIG. 13
, the diode element
70
is used for detecting the temperature of the substrate and is connected in forward biased fashion between an anode
62
and a cathode
64
, whereas the diode element
71
is connected in reverse biased fashion between the anode
62
and the cathode
64
for cramping a reverse voltage which may be generated in, for example, a control circuit. In detecting the temperature of the substrate, this temperature detecting diode element
70
generally relies on the temperature dependency of the forward going voltage VF between the anode
62
and the cathode
64
.
In practice, the reverse voltage cramping diode element
71
does not require the temperature dependency to be taken into consideration and, therefore, a single diode is employed therefor for minimizing a space occupied thereby on the substrate. On the other hand, temperature dependent change of the forward going voltage VF between the anode
62
and the cathode
64
of the temperature detecting diode element
70
is relatively small and, therefore, for the temperature detecting element
70
, a plurality of diodes connected in series with each other are generally employed to increase the temperature dependent change. By way of example,
FIG. 13A
illustrates, in a schematic plan view, the power semiconductor device in which the temperature detecting diode element
70
is comprised of two diodes
70
a
and
70
b
and the reverse voltage cramping diode element
71
is comprised of a single diode.
FIG. 13B
illustrates a cross-sectional representation taken along the line D—D in FIG.
13
A. In this power semiconductor device shown in
FIGS. 13A and 13B
, respective portions of the insulating layer
54
positioned immediately beneath the diodes
70
a
,
70
b
and
71
have an equal thickness.
It has, however, been found that the temperature detector
60
employed in the above described power semiconductor device
50
is susceptible to an erroneous operation that is brought about by external noises such as, for example, unwanted external electromagnetic waves and is therefore limited in application. Specifically, since the power semiconductor device
50
has parasitic capacitances, a difference occurs between an electromotive force generated in a forward going path of the diode element
70
and that generated in a negative going path of the diode element
71
when the temperature detector
60
is interfered with an external electromagnetic wave, resulting in an erroneous operation.
The parasitic capacitances referred to above will be discussed in detail. As discussed above,
FIG. 12
is an equivalent circuit diagram of the power semiconductor device
50
shown in FIG.
11
. Regions
56
and
58
of different conductivities opposite to each other that form the diode elements
70
and
71
, respectively, of the temperature detector
60
confront the p-type region
52
, which is a base region of the power semiconductor device
80
, through the insulating layer
56
. Considering that this p-type region
52
is held at a potential which is the same as the emitter potential and that the diode elements
70
and
71
forming respective parts of the temperature detector
60
are formed on the insulating layer
56
, a parasitic capacitance C
1
, C
2
, C
3
and C
4
is formed between the base region
78
and each of regions of respective conductivities of the diode elements
70
and
71
.
Hitherto, the presence of the parasitic capacitances C
1
to C
4
has not been recognized. In contrast, the inventors of the present invention have found that the presence of those parasitic capacitances brings about detrimental problems to the proper functionality of the temperature detector used in the power semiconductor device. By way of example, since the regions of the two different conductivities forming the respective diode elements have respective surface areas that are generally different from each other, the parasitic capacitances on respective sides of each of the diode elements are of different values, that is, C
1
≠C
2
and C
3
≠C
4
. Also, where the two diodes
70
a
and
70
b
are connected in series with each other to form the temperature detecting diode element as shown in
FIG. 13A
, the total capacitance generated between the diodes
70
a
and
70
b
and the base region
78
of the power semiconductor element
80
amounts to twice that generated between the reverse voltage cramping diode element
71
and the base region
78
, that is, C
1
=2×C
3
and C
2
=2×C
4
. Because of this, when an external noises such as the external electromagnetic wave interfere with the power semiconductor device
50
, a difference occurs between an electromotive force generated in the forward going path of the diode element
70
and that generated in the negative going path of the diode element
71
as hereinbefore described, resulting in an erroneous operation. A similar difference occurs even between an electromotive force generated in a circuit between the diode
70
a
and the cramping diode
71
and that between the diode
70
b
and the cramping diode
71
, resulting in an erroneous operation.
The Japanese Laid-open Patent Publications No. 8-236709, No. 10-116987 and No. 58-25264 discloses a semiconductor device in which a power element and a heat sensitive element formed on a common semiconductor substrate with an insulating layer intervening therebetween to prevent a parasitic action of the heat sensitive element. Even in the power semiconductor devices disclosed in those publications, since the heat sensitive element confronts the semiconductor substrate through the insulating layer, parasitic capacitances tends to be formed in a manner as discussed hereinabove. However, none of those publication address to the problem associated with the parasitic capacitances.
SUMMARY OF THE INVENTION
Accordingly, the present invention has been devised to provide an improved power semiconductor device having a temperature detector incorporated therein, which is substantially free from an erroneous operation which would otherwise be brought about under the influence of an external noise such as an external electromagnetic wave.
In accordance with one aspect of the present invention, there is provided a power semiconductor device which includes a power semiconductor element formed on a substrate and a temperature detector including a temperature detecting diode element having at least one diode formed on the substrate for detecting a temperature. The temperature detecting diode has two regions of conductivity types different from each ot
Mitsubishi Denki & Kabushiki Kaisha
Tran Minh Loan
Tran Tan
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