Short-Channel Effect Suppression In Silicon Carbide Power Mesfets
- PDF / 271,959 Bytes
- 5 Pages / 595 x 842 pts (A4) Page_size
- 74 Downloads / 188 Views
SHORT-CHANNEL EFFECT SUPPRESSION IN SILICON CARBIDE POWER MESFETS A. Konstantinov, A-M. Saroukhan, S. Karlsson, C. Harris and A. Litwin*. ACREO AB, Electrum-236, SE-164 40, Kista, Sweden Ericsson Microelectronics AB, SE-164 81, Kista, Sweden.
*
Abstract We demonstrate that the performance of silicon carbide MESFETs is largely determined by short-channel effects. Parasitic bipolar transistor turn-on limits the operation voltage to a small fraction of the theoretically expected value for an ideal device. Tradeoffs are shown to exist between optimum gate length and on-state current on one hand, and the maximum blocking voltage on the other hand. Composite p-buffers with an elevated doping in the vicinity of the active layer considerably increase the operation voltage. Silicon carbide MESFETs utilizing composite buffers are reported. Introduction
drain current
Silicon carbide is a promising material for microwave power device applications. However, the performance of today’s silicon carbide power microwave components does not meet theoretical expectations. In this paper we investigate the limitations originating from short-channel and suggest a technique for short-channel effect suppression. saturation load line
breakdown
(a)
drain current
drain bias ration no satu
(b) load
line
early turn-on
drain bias
Figure 1. I-V curve families for a classical (a) and a short-channel (b) FET.
Figure 2. Current contours for the early turn-on of a silicon carbide FET due to source-to-drain punchthrough, at a gate bias of –10 V and a drain bias of 100 V. The buffer layer doping is 2x1015 cm-3, the gate length is 1 µm.
H4.6.1
Schematically shown in Figure 1 are the curve families for classical longchannel and short channel power FETs. A high breakdown field in SiC is an advantage from the viewpoint of high power high frequency operation, since a high operation voltage can be achieved without increasing the drift region length and hence the carrier transit time. In addition, a high breakdown field also means a potentially higher sheet carrier density and a higher saturation current. A great improvement of device performance could be expected from utilizing SiC if transistor performance were indeed determined by the classical long-channel model. However, highfrequency operation requires short gates, and most high frequency transistors exhibit pronounced short-channel effects. The curve families for a short-channel transistor will have a slope in the saturation region, as it is shown in Figure 1b. This slope originates from drain-induced channel modulation [1]. The high field at the drain side will modulate the effective channel length and hence the drain current. Further increase of the drain potential will result in a turn-on of a parasitic bipolar transistor. In this transistor the source substitutes for emitter, the drain for collector and the ptype buffer layer (or substrate) acts as a base region. The turn-on of the parasitic bipolar transistor is in some cases called source-to-drain punchtrough. The gate bias requir
Data Loading...
