HIGH-VOLTAGE LATERAL POWER TRANSISTERS: THEORY AND DESIGN
The conventional high voltage power transistor is a vertical device. That is, one in which the current flow is vertical. This construction technique has evolved from both physical reasons and the relative ease of construction of these devices. Whether the device is a Field Effect Transister (FET) or a Bipolar Junction Transistor (BJT), this vertical current flow results in the substrate, that part of the silicon wafer on which the device is built, being the drain or the collector terminal. If it is wished to integrate circuitry to control the power device on the same chip, the fact that the substrate is a terminal which can change its potential as the load or device characteristics are varied, presents severe common mode problems. A lateral transistor, one in which all terminals are on the top of the chip and the resultant current flow is lateral to the top, can alleviate these problems to some extent. While this construction technique is not common, numerous examples of these devices exist in the literature. Generally these devices are either low voltage units or, for a given value of voltage/current capability, they use considerably more chip surface than a comparable vertical device. In this study, a new lateral device, The LAteral Bipolar Field Effect Transistor or LABFET, is described. This device replaces the normal n+-drain diffusion, used in the typical Double Diffused MOS (DMOS) transistor with a p-type diffusion. This p-diffusion acts as the emitter of a low gain p- n-p bipolar transistor. The base of this device is the n-substrate or n-well, when the device is part of an integrated circuit. The base current is supplied by turning on the DMOS Field Effect Transistor. The result is a conductivity modulated device, with all terminals on the top of the chip, a voltage withstand capability of 100 V and an on-staAte conductance of .71 Siemans per cm of gate width. This is comparable with conventional vertical FET devices. The static and dynamic characteristics of "Unit cell" devices are presented with an explanation of the results and a description of the processing to produce them. Finally, suggestions are made which would allow the extension of this concept to a large device suitable for integration into a power integrated circuit.
James Anthony Benjamin,
"HIGH-VOLTAGE LATERAL POWER TRANSISTERS: THEORY AND DESIGN"
(January 1, 1984).
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