Active solid-state devices (e.g. – transistors – solid-state diode – Schottky barrier – With means to prevent edge breakdown
Reexamination Certificate
1997-12-10
2001-01-23
Tran, Minh Loan (Department: 2811)
Active solid-state devices (e.g., transistors, solid-state diode
Schottky barrier
With means to prevent edge breakdown
C257S481000, C257S483000, C257S494000
Reexamination Certificate
active
06177712
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to Schottky barrier diodes, and in particular to small capacitance Schottky barrier diodes that are suitably used for a switching power supply, assuring a high destructive electric power level.
BACKGROUND OF THE INVENTION
High-speed diodes and Schottky barrier diodes are known as semiconductor devices having a rectifying function and used for a switching power supply and the like. The switching power supply having a high conversion efficiency is adapted to rectify alternating input voltage into direct voltage, convert the direct voltage into alternating voltage having a high frequency via an ON-OFF circuit, transform the alternating voltage by means of a transformer, and then rectify the resulting voltage again to convert it into direct voltage. In this switching power supply, Schottky barrier diodes having excellent high-speed switching characteristics are used as a device for performing high-frequency rectification. Significant factors for determining the efficiency of the switching power supply include a loss in the ON-OFF circuit and a forward voltage drop that occurs in the diode that performs the high-frequency rectification. In particular, the forward voltage drop in the diode is desired to be minimized so as to achieve a sufficiently high efficiency of the power supply.
However, since Schottky barrier diodes are limited to a relatively narrow range of rated voltage as compared with pn junction diodes, a circuit including the Schottky barrier diodes needs to be designed so that a reverse voltage greater than the rated voltage is not applied to the diodes. In addition, the occurrence of surge voltage must be taken into consideration. Thus, a device whose withstand voltage is one order higher than that required in the circuit design is generally used as Schottky barrier diode. Otherwise, if a voltage, such as surge voltage, that is higher than the rated voltage is applied to the Schottky barrier diode, avalanche breakdown occurs in the Schottky barrier diode, possibly causing destroy by electric power even at small current levels. Thus, the device having a high withstand voltage is selected as the Schottky barrier diode so as to minimize a possibility of the occurrence of avalanche breakdown in the Schottky barrier diode. In the meantime, the forward voltage drop is increased with an increase in the withstand voltage, which impedes an improvement in the efficiency of the power supply.
SUMMARY OF THE INVENTION
It is therefore an object of the present invention to provide a Schottky barrier diode that has a high withstand voltage and does not suffer from destroy by electric power even if high current flows due to avalanche breakdown, while assuring a sufficiently low forward voltage drop.
To accomplish the above object, there is provided a Schottky barrier diode comprising a substrate including a first-conductivity-type low concentration layer and a first-conductivity-type high concentration layer, and a guard ring region, comprising a second-conductivity-type diffusion layer having an impurity surface concentration of not greater than 5×10
17
/cm
3
, formed in the first-conductivity-type low concentration layer, wherein the first-conductivity-type low concentration layer has a thickness large enough to prevent a depletion layer that appears in the low concentration layer upon application of a maximum reverse voltage from reaching the first-conductivity-type high concentration layer.
In the Schottky barrier diode constructed as described above, the impurity surface concentration of the diffusion layer of the guard ring region is reduced down to 5×10
17
/cm
3
which is one order of magnitude smaller than that of known prior art diodes, whereby the slope of the impurity concentration of the diffusion layer becomes less steep. As a result, the depletion layer or region extends to a greater length in the diffusion layer, and avalanche breakdown is less likely to occur in the diffusion layer. Thus, breakdown that has occurred mainly in the diffusion layer in the prior art device is caused to occur in the first-conductivity-type low concentration layer of the substrate. The resulting Schottky barrier diode provides a high destroy by electric power level and is less likely to break down.
REFERENCES:
patent: 5081510 (1992-01-01), Ohtsuka et al.
patent: 58-058774A (1983-04-01), None
patent: 60-206179A (1985-10-01), None
R.A. Zettler et al., “Junction-Schottky Barrier Hybrid Diode”,Jan. 1969, pp. 58-63, IEEE Transactions on Electron Devices, vol.ED-16, No. 1.
K. Ichikawa et al., “Design Considerations for Power Schottky Barrier Diodes”, Jun. 1983, pp. 20-26,CH1855.
“Physics of Semiconductor Devices 2nd Edition”, Editor S.M. Sze, 1981, John Wiley & Sons, pp. 245-311.
Fuji Electric & Co., Ltd.
Rossi & Associates
Tran Minh Loan
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