Active solid-state devices (e.g. – transistors – solid-state diode – Regenerative type switching device – Combined with field effect transistor
Reexamination Certificate
1998-07-02
2001-01-30
Monin, Jr., Donald L. (Department: 2814)
Active solid-state devices (e.g., transistors, solid-state diode
Regenerative type switching device
Combined with field effect transistor
C257S144000, C257S152000, C257S501000, C257S506000, C257S635000, C257S510000
Reexamination Certificate
active
06180965
ABSTRACT:
TECHNICAL FIELD
The present invention relates to a semiconductor device, and more particularly to a lateral type static induction semiconductor device having a gate region provided in a recessed portion formed in a surface of a semiconductor substrate.
BACKGROUND ART
Conventional power semiconductor devices have been commonly used as a power supply device, and have been described in the following literatures.
1. Junichi Nishizawa: “High power-lateral junction FET of the character of a triode”, Nikkei Electronics, 50~61, Sep. 27, 1971
2. J. Nishizawa, T. Terasaki, and J. Sibata: “Field-Effect Transistor versus Analog Transistor (Static Induction Transistor)”, IEEE Trans. on Electron Device, ED-22(4), 185 (1975)
3. J. Nishizawa and K. Nakamura: Physiquee Appliquee, T13, 725 (1978)
4. J. Nishizawa and Y. Otsubo: Tech. Dig. 1980 IEDM, 658 (1980)
5. Junichi Nishizawa, Tadahiro Omi, Moken Sha, and Kaoru Hontani: “Denshi-Tsushin Institute Technical Research Report”, ED81-84 (1981)
6. M. Ishidoh et al: “Advanced High Frequency GTO”, Proc. ISPSD, 189 (1988)
7. B. J. Baliga et al: “The Evolution of Power Technology”, IEEE Trans. on Electron Device, ED-31, 157 (1984)
8. M. Amato et al: “Comparison of Lateral and Vertical DMOS Specific On-resistance”, IEDM Tech. Dig., 736 (1985)
9. B. J. Galiga: “Modern Power Device”, John Wiley Sons, 350 (1987)
10. H. Mitlehner et al: Proc. ISPSD, 289 (1990): “A Novel 8 kV Light-Trigger Thyristor with Over Voltage Self Protection”
The above mentioned static induction semiconductor device has a device structure of a short-channel and a multi-channel in order to obtain low conduction loss, large current capability, high breakdown voltage, and high speed operation. In order to improve the high speed operation among these properties, it has been known to control a lifetime of carriers by diffusing Au, Pt and so on or by performing irradiation with electron beam or proton. In order to improve the large current capability, it has been also known to increase a surface area of a semiconductor device is suggested to obtain large current.
In the conventional static induction semiconductor device, if a part of a gate region is short-circuited to a cathode electrode, a channel region could not be pinched-off by a reverse-bias voltage because a gate current for turn-off is bypassed through the short-circuited region. That is, carriers existent in a N
−
region (including the channel region) at turn-off could not be swept out due to the short-circuit of the gate region to the cathode region. In other words, in the semiconductor device having a large surface area, an influence of resistance between the gate region and a point at which a lead wire for the gate region is drawn out cannot be neglected. Therefore, a large current could not be cut-off at a high speed due to a fact that a voltage drop is produced by a gate current of carriers flowing from the gate region to the drawn-out point of the lead wire of the gate electrode at turn-off and the turn-off operation might be effected by this voltage drop.
Moreover, when a high speed operation is attained by controlling lifetime of carriers, there is another problem that a conduction loss is increased due to a high on-resistance.
It is an object of this invention to solve the above problems of the conventional semiconductor devices and provide a semiconductor device, in which carriers remained within the gate region and N
−
base region can be swept out immediately at turn-off to increase a switching speed, while the low conduction loss, large current capability and high breakdown voltage can be maintained as there are.
It is another object of this invention to provide a semiconductor device, in which a switching speed can be increased and at the same time a conduction loss is decreased by reducing on-resistance.
DISCLOSURE OF INVENTION
According to the invention, a semiconductor device is characterized in that it comprises a semiconductor substrate of one conductivity type having first recessed portions formed in one surface thereof, gate regions of the other conductivity type formed along the first recessed portions, cathode regions of the one conductivity type formed on the surface of the semiconductor substrate surrounded by the gate regions, cathode short-circuit regions of the other conductivity type surrounded by the cathode regions and channel regions formed by the semiconductor substrate of the one conductivity type, and a cathode electrode substrate made of a metal or semiconductor and being brought into contact with the surfaces of the cathode regions and cathode short-circuit regions.
In the semiconductor device according to the present invention, at turn-off, carriers existent within the channel region can be swept out directly into the cathode electrode through the island-like cathode short-circuit region of the same conductivity type as the gate region surrounding the channel region, and thus a large current can be cut-off at a high speed. That is to say, according to the invention, when a gate voltage for turn-off is applied across the gate electrode and the cathode electrode, the cathode short-circuit region (P
+
layer) of the other conductivity type surrounded by the cathode region (N
+
layer) and channel region (N
−
region) is isolated from gate region with a high resistance by means of a depletion layer produced in the channel region when the P
+
N
−
junction between the gate region (P
+
layer) and the channel region (N
−
region) is reverse-biased. Therefore, the gate current for turn-off is not bypassed through the cathode short-circuit region, and a normal turn-off operation can be performed. Moreover, a large current can be cut off at a high speed because holes existent within the N
−
region and channel region can be swept out to the cathode electrode immediately through the cathode short-circuit region, that is, a region having a low resistance. Furthermore, a switching loss can be made small and a maximum switching frequency can be made high because residual carriers at turn-off can be swept out directly to the cathode electrode at a high speed.
In a preferable embodiment of the semiconductor device according to the invention, the cathode region is provided in the form of an island which is surrounded by the second recessed portion, the cathode region is composed of plural projected portions of the other conductivity type formed in the one surface of the semiconductor substrate of the one conductivity type, the second recessed portion is formed to surround the plural projected portions of the other conductivity type, and the cathode region of the one conductivity type is formed projected portions which define said second recessed portions and gate region.
According to the invention, it is preferable to provide an insulating layer, which covers gate region of the other conductivity type formed along the first recessed portion formed in the surface of the semiconductor substrate of the one conductivity type, or a cathode electrode made of metal or semiconductor is preferably formed to be contacted with the gate region through an opening formed in the insulating layer.
Moreover, in order to reduce an on-resistance for attaining a low loss, it is preferable that the semiconductor substrate of the one conductivity type is made of silicon, and an Au—Sb, Al—Si or Al—Sb alloy layer or Al layer is formed on the surface of the cathode electrode substrate which is brought into contact with the cathode region and cathode short-circuit region, that a high impurity concentration regions of the one conductivity type is formed on the cathode region to be contacted with the cathode electrode substrate, or that a metal layer is formed on the surface of the cathode region which is contacted with the metal plate. Especially in the case of forming the above alloy layer or Al layer, good contact can be obtained under pressure during the package and good electrical contact can be attained, so that a contact resistance can be made low.
The on resistance can
Bentley Dwayne L.
Monin, Jr. Donald L.
NGK Insulators Ltd.
Parkhurst & Wendel L.L.P.
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