Wide Bandgap Semiconductors for Microwave Power Devices Dr. C. E. - PowerPoint PPT Presentation

Wide Bandgap Semiconductors for Microwave Power Devices Dr. C. E. Weitzel Consultant: Wide Bandgap Power Devices

Presentation Outline • Why Wide Bandgap Semiconductors? • SiC Microwave Power Devices • What are FET Field‐Plates? • AlGaN/GaN Microwave Power Devices

The Rest of the Wide Bandgap story • SiC produced the first commercial BLUE LED’s • GaN produced first high brightness BLUE LED’s • GaN based materials enabled and dominate the LED commercial market • Low intrinsic carrier concentraKon enables significantly higher operaKng temperatures • GaN‐on‐Si looks promising for Switching Power Devices to compete with silicon IGBT’s, silicon MOSFET’s, and SiC MOSFET’s.

Why Wide Bandgap Semiconductors? RelaKve Cost $ $$ $$$$$ $$$$$ $$$$ $$$$$$$$$$ B. Ozpineci and L.M. Tolbert, “Comparison of Wide‐Bandgap Semiconductors for Power Electronic ApplicaKons,” Oak Ridge NaKonal Laboratory, December 12, 2003

Diode Breakdown Voltages • Wide bandgap enables high breakdown voltages • This enables a tradeoff between operaKng voltage and current, but in either case boosts power handling capability B. Ozpineci and L.M. Tolbert, “Comparison of Wide‐Bandgap Semiconductors for Power Electronic ApplicaKons,” Oak Ridge NaKonal Laboratory, December 12, 2003

Diode Drift Region Resistance • Wide bandgap enables lower device resistance for a given voltage • Lower resistance enables higher operaKng current B. Ozpineci and L.M. Tolbert, “Comparison of Wide‐Bandgap Semiconductors for Power Electronic ApplicaKons,” Oak Ridge NaKonal Laboratory, December 12, 2003

RF Power Density / Operating Voltage 48V

Micropipes Result from Screw Dislocation

Reduction of Micropipe Density / Wafer Size

Very Low Micropipe Density SiC Wafer

SiC MESFET --- the first wide bandgap microwave power transistor SiC MESFET’s, SiC MOSFET’s & SiC SIT’s

Probably Highest SiC MESFET power density ever reported I would certainly like to know more details about this device

High power 4H‐SiC staKc inducKon transistors (SITs) SEM photo of a SIT device. The mesa fingers are 1 µm wide and 100 µm long. The total mesa length is 1 cm Measured staKc I‐V characterisKcs of a SIT (100 fingers).

Microsemi introduced a 2.2kW SiC SIT in Sept. 2010

What are Field-Plates? aka - Step-Gates, Faraday Shields, Source connected Field-Plates Field‐plate is a metal structure added to a FET between the gate and drain that increases the microwave gain and/or breakdown voltage (Si, GaAs, SiC, GaN).

Microwave Field-Plates • First demonstraKon of field‐plate on microwave transistor (GaAs) • Source connected field‐plate sits on top of a dielectric • RF gain is increased by making the device more unilateral Source • C GD is reduced at the expense of C GS Gate and C DS Field Plate Drain • Can also increase breakdown voltage if properly designed Dielectric

Field‐Plate increases small signal gain approx. 3 dB

1.7 W/mm 1.5 GHz Vds = 35V

2003

Field‐Plate increases CW gain 2 dB

AlGaN–GaN Field Effect Transistor ‐ the SiC MESFET “KILLER”

Basic AlGaN‐GaN HeterojuncKon FET +++++++++++++++++++++ Substrate: Sapphire, SiC, or Silicon Spontaneous and Piezoelectric PolarizaKon cause +++ charge in the AlGaN. The band structure forms a quantum well at the AlGaN‐GaN interface. Electrons fill the quantum well to a very high density > 1E7 cm ‐2 . There is no intenKonal doping.

Small Signal GaN HFET reported at SiC Conference in Kyoto, Japan

12.6 mm AlGaN/GaN HFET 48 V 2.14 GHz 74 W 5.9 W/mm No Field Plate IMS 2006

AlGaN/GaN HFET 30 V 15 GHz 60 W ~ 3 W/mm IMS 2010

Wide Bandgap Summary • Material properKes: ‐ high operaKng voltages ‐ high thermal conducKvity (SiC substrate) • SiC MESFET first wide bandgap microwave power transistor • Field Plates: ‐ increased RF gain ‐ even higher operaKng voltages • AlGaN/GaN heterojuncKon achieves current density > 1 x 10 13 A/cm 2 (SiC MESFET “killer”) • Heavily supported for US defense applicaKons, but is there a “killer” commercial applicaKon??