6H silicon carbide MOSFET modelling for high temperature analogueintegrated circuits (25-500°C)

摘要

The authors report on the effects of elevated ambient andnsubstrate temperatures (25-500°C) on the electrical characteristicsnof 6H polytype silicon carbide (SiC) MOSFETs. The work focuses primarilynon modelling the temperature variations of the large- and small-signalnparameters of the devices with a view to assessing their suitability fornhigh-temperature integrated electronics. These parameters includenthreshold voltages, leakage currents, body-bias effects, andnsmall-signal transconductances and output conductances. Where relevant,nthe authors' results are compared to silicon MOSFETs and GaAs MESFETs.nAbove 225°C, the parameter variations of their SiC MOSFETs,nincluding the observation of zero temperature coefficient (ZTC) drainncurrents, are qualitatively similar to those of Si MOSFETs and of GaAsnMESFETs. In contrast with silicon MOSFETs. However, the gatentransconductance (gm) and the channel mobility (Μ)nincrease with increasing temperature up to 225°C approximatelynbecause of a high interface state density. The ON/OFF current ratio ofntheir SIC MOSFETs is at least two orders of magnitude higher than for Sinand GaAs FETs above 200°C. Junction leakage current densitiesnmeasured up to 500°C are several orders of magnitude lower than innhigh quality Si and GaAs devices, as expected from the higher bandgapnenergy for their SiC material (≈3 eV). While the junctions retainedntheir electrical integrity, their MOSFETs displayed large gate-to-drainnleakage currents above 300°C, apparently due to an oxide reliabilitynproblem. Pin-to-pin package leakage is also observed above the samentemperature. Despite this partial form of damage, the authors believenthat their results confirm the expected potential of SIC MOSFETs fornintegrated circuit applications above 250°C. The data reported innthe paper, for this novel SIC process, are used to derive MOSFET modelsnand SPICE parameters for analogue IC design, and an NMOS operationalnamplifier (OPAMP) is presented which is expected to operate in the rangen25°C to 500°C, where silicon and GaAs technologies arenunsuitable