Study On Temperature Characteristics Of SiC MOS Device And Circuits

Silicon Carbide(SiC) is a very promising candidate for high temperature, high power, high frequency, relatively low noise and radiation hardness applications due to its excellent physical properties such as a wide bandgap, high breakdown voltage, high thermal conductivity, and high saturation electron drift velocity. Based on MOS processing technology, SiC metal-oxide-semiconductor field-effect transistor(MOSFET) and digital/analogue circuit have been granted with considerable attention and intensively investigated.In this work, emphasis is laid on researching on temperature dependence of SiC MOSFET, CMOS inverter and OPAMP, In addition, experimental results of 4H-SiC NMOS and ohmic contact have been given. All works and contributions as follows:(1) Based on an analytical solution of the Poisson equation, interface fixed charge and trapped charge in different temperature is separated analytically; parameters of Gauss profile is also determined; Considering the influence of the incomplete ionization of deep-lying impurity, electron velocity saturation, non-uniform profile of interface trap and different surface scattering mechanisms, a detailed simulation and study of effects of trapped interface charge on DC and transient characteristics of device by ISE is done with an appropriate set of initial trap occupation. The comparison between simulations and physical measurements shows a good agreement. This simulation simplified a complex recombination processing of charge with interface trap as follows: When temperature increasing, increasing of electron kinetic energy limits the number of interface trapped charge, thus surface total mobility increase for Coulomb scattering weakening. Zero Temperature Coeffient Point, which is the result of a trade-off between the decreasing surface mobility and the increasing impurity ionization, emerge when temperature is higher than 450K; Transient simulation shows that the peak current is limited by the number of fast interface state occupied and the number of slow near interface states and their capture cross-sections give the delay in the current.(2) Effects of all kinds of scattering machnisms on device is studied. Separation of interface scattering mobility is done with interface trap's non-uniform profile. And the dominant scattering mechanism responsible for device operating in high temperature and high voltage is determined:Inversion mobility is almost established by Coulomb scattering even temperature higher up to 600K, only at higher temperature and higher gate bias is the inversion mobility being affected by other scattering mechanisms.(3) Influence of temperature on breakdown in anisotropic 6H-SiC MOSFET is studied. Considering the anisotropy of material, anisotropy of the breakdown is obtained in different face but the tendency of breakdown voltage vs. temperature is same, both have positive temperature coefficient. For improving breakdown characteristics of device, electric field oritention should be parallel to C axis, or magnitude of electric field perpendicular to C axis is lower than that of parallel to C axis.(4) For increasing channel effective mobility of SiC PMOSFET, buried channel PMOS is adopted. Analytical model of BC PMOS considering incomplete ionization of impurity is established. Reasonable of such structure and temperature dependence of BC PMOS is basically studied.(5) Comparison of SiC CMOS inverter with Si counterpart in different temperature is done. And some static property parameters are extracted. Characteristics of SiC CMOS inverter, when applied to digital circuit, is included.(6) Simulation of temperature dependence of SiC CMOS OPAMP, which is designed based on Zero-Temperature-Coefficient(ZTC) and leakage current matching, is done. Differential Model equivalent circuit and Common Model equivalent circuit are derived from high temperature model of MOSFET, in addition, high temperature gain is given. Simulation is done with Hspice Level 11. Simulation results has shown:For a lower channel effective mobility of SiC MOSFEET results a lower transconductance than that of Si MOSFET, SiC OPAMP has a lower Open Loop Gain than that of Si counterpart, the parameter of SiC OPAMP will vary with temperature though a stability output characteristics is obtained at a single temperature. A primary discussion of high temperature layout design is also given.(7) Under the fabrication ability of our own, some experimental results about 4H-SiC NMOSFET and ohmic contact is obtained:One is a preferable N-type and P-type ohmic contact of about 10-5Ω·cm 2 by ion implantation to P-type material, which can satisfied requirement of device manufacture, The other is a sound NMOS with favorable linearity and saturation characteristics, which has a threshold voltage about 1V and a transconductance about 18mS/mm with a channel length of 5μm.