Miscellaneous active electrical nonlinear devices – circuits – and – Gating – Utilizing three or more electrode solid-state device
Reexamination Certificate
1999-06-15
2001-06-05
Wells, Kenneth B. (Department: 2816)
Miscellaneous active electrical nonlinear devices, circuits, and
Gating
Utilizing three or more electrode solid-state device
C327S374000, C327S483000, C327S575000
Reexamination Certificate
active
06242967
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to a semiconductor device in which a bipolar transistor or transistors are connected to unipolar transistors, which device exhibits low ON resistance and a high-speed switching characteristic.
BACKGROUND OF THE INVENTION
Individual semiconductor switching devices or elements, which have low ON resistance and exhibit a high-speed switching characteristic, include bipolar transistors and unipolar transistors. For example, insulated gate field-effect transistors (hereinafter abbreviated to “MOS transistor”) are well known as an example of the unipolar transistors. Also, insulated gate bipolar transistors (hereinafter referred to as “IGBT”) that are voltage-controlled bipolar transistors have been increasingly used in recent years. These semiconductor devices have the following features.
The bipolar transistor may use a high-resistivity substrate to form a collector layer, in order to ensure a high breakdown-voltage characteristic. Even with the use of such a high-resistivity substrate, the transistor of this type undergoes conductivity modulation based on injection of minority carriers while the device is used in a saturation mode, thus assuring reduced ON resistance. However, the turn-off time is increased due to the effect of accumulation of the minority carriers, resulting in a delay in switching the transistor.
The MOS transistor that is a unipolar transistor is inherently free from accumulation of minority carriers, and therefore operates at a high switching speed. This type of transistor, however, suffers from relatively large ON resistance since the conductivity modulation based on injection of minority carriers does not occur in this device.
Similarly to the bipolar transistor as described above, the IGBT exhibits relatively low ON resistance, but suffers from relatively long turn-off time due to the effect of accumulation of minority carriers. In addition, minority carriers are re-injected from the collector layer, due to electrons that are discharged by a depletion layer that spreads out during turn-off, which results in an increase in the turn-off time.
In a conventional switching circuit, therefore, bipolar transistors and IGBT, which have a small steady-state loss but suffer from a large switching loss, are often used at a relatively low frequency (generally, lower than 50 kHz), while MOS transistors, which have a small switching loss but suffers from a large steady-state loss, are often used at a relatively high frequency (generally, 100 kHz).
In an intermediate frequency region, namely, in the range of 20-100 kHz, it is desirable to use a semiconductor device having the characteristics of both of the above types of transistors, depending upon its applications.
FIG. 51
shows one example of this type of semiconductor device as disclosed in Japanese Laid-open Patent Publication No. 62-293678. This example is a so-called BiMOS-Cascade transistor in which a unipolar transistor UT is provided in the front stage, and a bipolar transistor BT is provided in the rear stage. This semiconductor device exhibits low ON resistance, and can be controlled by voltage, but suffers from a problem that the turn-off time, in particular, storage time, is considerably increased because an excessive amount of carriers stored in the bipolar transistor BT during turn-off cannot be removed or drawn away from the transistor BT.
To overcome this problem, there has been proposed a semiconductor device as shown in FIG.
52
, wherein a resistor R is provided between the base and emitter of the bipolar transistor BT. Examples of this type of semiconductor device are disclosed in Parpia, Z. et al., IEEE Trans. on ED, vol.33, 1984 (1986), ibid. vol.35, 1687, (1988), Narayanan, S. et al., IEEE ISPSD '91, 103, (1991), Narayanan, S. et al., IEEE Trans on ED, 1624, (1991), Godignon, P. et al., MADEP, 0-215, (1991), Ajit, J. S. MADEP, 0-148, (1991), Godignon, P. et al., Solid-state Electronics, 1777, (1996). In this type of semiconductor device, carriers may be drawn away from the base region of the bipolar transistor BT through the resistor R during turn-off, and therefore the turn-off time can be shortened. However, the ON resistance is somewhat increased since current flows through the resistor R during turn-on as well as turnoff. As another method for solving the problem of increased turn-off time, a semiconductor device as shown in
FIG. 53
has been proposed in Japanese Patent No. 3-66816, wherein a diode D is connected between the base of a bipolar transistor BT and the gate of a unipolar transistor UT. During turn-off of this semiconductor device, carriers can be drawn from the base region of the bipolar transistor BT into the gate through the diode D, and therefore the turn-off time can be shortened. However, a small amount of carriers still remain due to a barrier-layer voltage at the junction of the diode D.
SUMMARY OF THE INVENTION
It is therefore an object of the present invention to provide a semiconductor device suitable for use as a switching device, which exhibits sufficiently low ON resistance, and a high-speed turn-off characteristic.
To achieve the above object, the present invention provides a semiconductor device comprising: a first unipolar transistor provided in a front stage of the device and including a drain, a source and a gate; a second unipolar transistor provided in the front stage and including a drain, a source, and a gate; and a bipolar transistor provided in a rear stage of the device and including a collector, a base, and an emitter. In this semiconductor device, the drain and the source of the first unipolar transistor are connected to the collector and the base of the bipolar transistor, respectively, and the drain and the source of the second unipolar transistor are connected to the emitter and the base of the bipolar transistor, respectively.
Upon turn-on of the semiconductor device as described above, the first unipolar transistor is turned on, and the second unipolar transistor is turned off, so that the bipolar transistor is turned on. To turn off this device, on the other hand, the first unipolar transistor is turned off, to stop supply of the base current to the bipolar transistor, so that the bipolar transistor is turned off. At the same time, the second unipolar transistor is turned on, so as to draw an excessive amount of carriers away from the bipolar transistor, so as to increase the rate or speed of turning off the device.
In one preferred form of the invention as described above, the bipolar transistor provided in the rear stage comprises a plurality of Darlington-connected bipolar transistors, and the second unipolar transistor comprises a plurality of second unipolar transistors that respectively correspond to the Darlington-connected transistors. The source of each of the second unipolar transistors is connected to the base of a corresponding one of the Darlington-connected bipolar transistors, and the drain of each second unipolar transistor is connected to the emitter of one of the bipolar transistors that is located in the last stage. In this arrangement, it is possible to draw an excessive amount of carriers from each of the bipolar transistors that are connected in the Darlington configuration.
In the above form of the invention, the area of the bipolar transistor located in the latter stage of the Darlington-connected bipolar transistors may be made larger than the area of the bipolar transistor located in the former stage. With this arrangement, large main current of the latter-stage bipolar transistor can be favorably controlled, using the main current of the former-stage bipolar transistor as its base current.
In the above form of the invention, the area of the second unipolar transistor connected to the bipolar transistor located in the latter stage of the Darlington configuration may be made larger than that of the second unipolar transistor connected to the bipolar transistor located in the former stage. In this arrangement, even where the base current of the bipolar transistor i
Harada Yuichi
Iwaana Tadayoshi
Iwamuro Noriyuji
Shigekane Hisao
Fuji Electric & Co., Ltd.
Luu An T.
Rossi & Associates
Wells Kenneth B.
LandOfFree
Low on resistance high speed off switching device having... does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Low on resistance high speed off switching device having..., we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Low on resistance high speed off switching device having... will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-2542555