Active solid-state devices (e.g. – transistors – solid-state diode – Regenerative type switching device – Combined with field effect transistor
Reexamination Certificate
2001-11-07
2002-09-10
Loke, Steven (Department: 2811)
Active solid-state devices (e.g., transistors, solid-state diode
Regenerative type switching device
Combined with field effect transistor
C257S146000, C257S370000, C257S378000
Reexamination Certificate
active
06448587
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to a circuit incorporated IGBT in which an IGBT and a circuit are formed in a semiconductor substrate.
An insulated gate bipolar transistor (hereinafter abbreviated to IGBT) is a voltage controlled switching element which can control a current of a main terminal by a voltage of a control terminal. Since a large current and switching at a high frequency are possible, IGBT's are being used at the present time in a wide field of applications from household air conditioners to inverters of electric cars and so forth.
Hitherto, the contemplation of a low loss and a high speed was made for IGBT's. In recent years, not only the low loss and the high speed but also a high functionality have been promoted. A high-function IGBT includes, for example, an IGBT in which the IGBT is integrated with a protection circuit so that a protecting function is possessed by one chip. A problem encountered in integrating an IBGT with a circuit is an erroneous operation of the circuit caused by a carrier current or hole current peculiar to the IGBT. When a hole current injected from a collector layer of the IGBT flows into a circuit area, an erroneous operation of the circuit occurs. There has been disclosed a structure in which a layer for ejecting holes is provided in order to prevent the hole current from flowing into the circuit area.
FIG. 11
shows the cross-sectional structure of a circuit integrated IGBT having a hole ejecting layer. In
FIG. 11
, reference numeral
101
denotes a collector layer, numeral
102
a buffer layer, numeral
103
a drift layer, numeral
104
a channel layer, numeral
105
an emitter layer, numeral
106
a hole ejecting layer, numeral
110
an emitter electrode, numeral
111
a gate electrode, numeral
112
a gate oxide film, numeral
114
a source electrode, numeral
115
a MOSFET gate electrode, numeral
116
a drain electrode, numeral
117
a collector electrode, numeral
131
a source layer, numeral
132
a base layer, numeral
133
a drain layer, numeral
150
an IGBT area, numeral
151
a circuit area, and numeral
152
a lateral MOSFET. Though not shown in
FIG. 11
, resistors, diodes and so forth are formed as circuit forming elements other than the MOSFET in the circuit area
151
. Similarly, though not shown, the source electrode
114
, gate electrode
115
and drain electrode
116
of the MOSFET are connected to the other elements formed in the circuit area and the emitter electrode
110
and gate electrode
111
of the IGBT. In a turned-on condition of the IGBT, a hole current flows from the collector layer to the emitter layer, as shown by arrow in FIG.
11
. In order to suppress the flow of this hole current into the circuit area, the hole ejecting layer
106
is provided to prevent the hole current from flowing from the IGBT area into the circuit area.
In recent years, however, the high functionality and high preciseness of a circuit integrated in an IGBT have been advanced and there has been generated a problem that an erroneous operation of the circuit occurs even with a very small leakage current of holes. This is because even if the hole ejecting layer
106
is provided, a very small amount of holes may leak into the circuit area. Such an erroneous operation is remarkable in the case where an IGBT is integrated with a source follower circuit using a MOSFET.
FIGS. 12 and 13
show the cross section and the equivalent circuit of an IGBT integrated with a source follower circuit. In
FIGS. 12 and 13
, the same constituent elements as those in
FIG. 11
are denoted by the same reference numerals as those used in FIG.
11
. In
FIGS. 12 and 13
, reference numeral
140
denotes a source follower resistor, numeral
201
an n-channel MOSFET corresponding to a channel portion of the IGBT, numeral
202
an npn transistor composed of the drift layer, the channel layer and the emitter layer, numeral
203
a pnp transistor of an MOSFET composed of the collector layer, the buffer layer, the drift layer and the channel layer, numeral
204
an npn transistor of a MOSFET composed of the drift layer, the base layer and the emitter layer, and numeral
205
the lateral MOSFET.
In the conventional structure, a leakage hole current flows into the source electrode
114
of the MOSFET through the base layer
132
. When the hole current flows into the source electrode, a voltage generated across the source follower resistor
140
becomes higher than a desired voltage, thereby causing an erroneous operation of the circuit.
The present invention is made taking the above problem into consideration and provides a circuit incorporated IGBT which can prevent an erroneous operation of a circuit.
SUMMARY OF THE INVENTION
A circuit incorporated IGBT according to the present invention is provided with a semiconductor substrate having an IGBT area and a circuit area which are adjacent to each other. In a semiconductor layer of one conductivity type in which a circuit element is formed in the circuit area, there is provided another semiconductor layer of another conductivity type which adjoins the circuit element and has an impurity concentration higher than that of the semiconductor layer of the one conductivity type. An electrode contacts such other semiconductor layer and this electrode is connected to an electrode of an IGBT in the IGBT area.
According to the present invention, carriers are ejected from the second semiconductor layer to the electrode of the IGBT, thereby making it possible to prevent an erroneous operation of a circuit.
The one conductivity type may be p type or n type. The electrode of the IGBT is, for example, an emitter electrode. Carriers are holes or electrons.
REFERENCES:
patent: 5245202 (1993-09-01), Yasukazu
patent: 5304802 (1994-04-01), Kumagai
patent: 5631494 (1997-05-01), Sakurai et al.
patent: 5672893 (1997-09-01), Tihanyi
patent: 5703385 (1997-12-01), Zambrano
patent: 5777367 (1998-07-01), Zambrano
patent: 5798538 (1998-08-01), Nadd et al.
patent: A5235363 (1994-09-01), None
Kohno Yasuhiko
Mori Mutsuhiro
Uruno Junpei
Antonelli Terry Stout & Kraus LLP
Hitachi , Ltd.
Hu Shouxiang
Loke Steven
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