Mihir Mudholkar

Datasheet Driven Silicon Carbide Power MOSFET Model

A compact model for SiC Power MOSFETs is presented. The model features a physical description of the channel current and internal capacitances and has been validated for dc, CV, and switching characteristics with measured data from a 1200-V, 20-A SiC power MOSFET in a temperature range of 25°C to 225°C. The peculiar variation of on-state resistance with temperature for SiC power MOSFETs has also been demonstrated through measurements and accounted for in the developed model. In order to improve the user experience with the model, a new datasheet driven parameter extraction strategy has been presented which requires only data available in device datasheets, to enable quick parameter extraction for off-the-shelf devices. Excellent agreement is shown between measurement and simulation using the presented model over the entire temperature range.

Characterization and Modeling of 4H-SiC Lateral MOSFETs for Integrated Circuit Design

A new process in 4H-SiC is developed that features n-type buried and inversion channel lateral MOSFETs that are fabricated with several different channel lengths (2-8 μm) and widths (8-32 μm ) and characterized over a wide temperature range (25°C-225°C). It is shown that the on-resistance of enhancement-mode SiC MOSFETs reduces with temperature despite a reduction in inversion mobility because of the interaction of interface states with temperature. To enable integrated circuit development using the developed MOSFETs, their electrical characteristics are modeled over geometry and temperature using the industry standard PSP MOSFET model. A new mathematical formulation to describe the presence of the interface states is also developed and implemented in the PSP model, and excellent agreement is shown between measurement and simulation using the modified PSP model.

Characterization and modeling of SiC Junction Barrier Schottky diode for circuit simulation

A physics based compact model for SiC Junction Barrier Schottky (JBS) diodes is presented which features a comprehensive physical description of the DC and CV behavior of SiC JBS diodes. For the first time, modeling of leakage current for JBS diode in circuit simulation is done. The model includes temperature scaling of its parameters to enable modeling of the diodes over a wide range of temperature (25 °C to 175 °C). The model has been validated using characterization data from a 1200 V, 3 A SiC JBS diode from GeneSiC. Excellent agreement is shown between device measurements and simulation for all regimes of operation of the diode.

Carrier separation technique to optimize conductivity modulation in high voltage rectifiers

Hybrid power rectifier structures like Junction Barrier Schottky (JBS) rectifier and Trench JFET Schottky rectifier (TJFET) employ a combination of minority and majority carrier conduction to offer the superior on-state and switching performance of Schottky rectifiers, along-with the superior reverse leakage and breakdown characteristics of PiN rectifiers. In such structures, it is important to properly tune the conductivity modulation to achieve the desired forward voltage drop (VF) and stored charge (QRR) trade-off for any given application. Some structures also employ lifetime control techniques to improve the switching speeds. This paper presents a new method based on carrier separation technique to properly quantify and optimize the amount of conductivity modulation in hybrid rectifier structures, and can be easily extended to other similar power device structures.

Trench schottky rectifiers with non-uniform trench depths

A design methodology to optimize the drift region doping properties in trench Schottky rectifiers has been presented. Advanced lithography is being used for trench devices that are designed for smaller die sizes in wireless applications. Such devices feature narrow active trenches to maximize active area utilization in combination with a wide termination trench to support the breakdown voltage. Such different trench aspect ratios create a depth mismatch, if they are formed in a single etch step. It has been shown that designing the drift region while accounting for the trench depth difference is vital to properly optimize the device electrical parameters. A new trench architecture has also been proposed which features alternating deeper active trenches. The new trench architecture is shown to have the best performance trade-off at the cost of one additional mask step.

Manufacturing optimization for Silicon Trench rectifiers using NiPt salicide

The purpose of this study was to provide a low cost manufacturing solution for Silicon Trench based Schottky rectifiers utilizing NiPt alloy composition that produces multiple barrier heights and provide designers the option to easily adjust the barrier height (BH) for rectifier designs. Higher temperatures needed to obtain larger barrier heights are generally unfavorable for trench-based Schottky rectifiers. The silicides in trench rectifiers are separated by relativity small distances with nonreactive material (such as silicon oxide) and with high energy anneals and the silicon from the substrate will migrate creating a Ni(Pt)Si bridge between adjacent silicides. Additional issues arise from thicker Ni(Pt)Si growth near the gate oxide interface causing localized high silicon stress. Both these issues cause device performance issues such as increased diode leakage. Most common industry solution is to change the %Pt in the Ni alloy thus modulating the BH. A low cost solution is to use one NiPt alloy to meet multiple BH needs by changing the anneal conditions and adding a Ti “Cap” to the NiPt film.

A novel trench Schottky rectifier structure with controlled conductivity modulation

A Trench MOS Barrier Schottky rectifier (TMBS) structure with a novel conductivity modulation scheme has been presented. The conductivity modulation in the structure is achieved by using remote conductivity modulation (RCM) centers in the mesa regions, with varying frequency and doping profiles to achieve the desired trade-off between forward voltage drop and switching speed of the device. Using the new modulation scheme, devices with low forward voltage drop or low switching speeds can be obtained without the need for any lifetime control in the drift region. The RCM scheme has been implemented in a 200 V, 30 A trench Schottky device, and it has been demonstrated experimentally that by employing the RCM scheme, best-in-class forward voltage drop, breakdown voltage and switching speed are achieved.