SiC MESFET

Rajesh C. PandaEEL 6935

WBG ISpring 2003

Outline

• Introduction• Literature Review• Theory of MESFET Operation• Advantage of SiC MESFET• SiC Basic MESFET Structure• MESFET Specifications• SiC MESFET Application• Summary

Literature Review• K. P. Hilton, M. J. Uren, D. G. Hayes, P. J. Wilding, H. K. Johnson, J. J. Guest and B. H. Smith,

"High power microwave SiC MESFET technology", in Workshop on High Performance Electron Devices for Microwave and Optoelectronic Applications, EDMO, 1999, pp. 71-74.

• S.T.Allen, J.W.Palmour, ,C.H.Carter,Jr., C.E.Weitzel, K.J.Nordquist, and L.L.Pond, III, “Silicon Carbide MESFET’s With 2 W/mm and 50% P.A.E. at 1.8 GHz ” IEEE MTT-S Symposium Digest, San Francisco, CA, June, 1996, pp. 681-684.

• ST Allen, RA Sadler, TS Alcorn, JW Palmour, CH Carter, "Silicon Carbide MESFET‘s for High Power S-Band Applications”, 1997, IEEE MTT-S Digest, pp. 57-60.

• SP Murray and KP Roenker, “An Analytical Model for SiC MESFETs,” Solid State Electr. vol. 46 (10), pp. 195-198, October 2002.

• KE Moore, CE Weitzel, Kevin J. Nordquist, Lauren L. Pond, III, John W. Palmour, Scott Allen, and Calvin H. Charter, Jr., “ 4H-SiC MESFET with 65.7 % power added efficiency at 850 MHz”, IEEE Electron Device Letters, Vol.18, No.2, February 1997.

• Inder Bahl and Prakash Bhartia, Microwave Solid State Circuit Design, A Wiley-Interscience Publication, 1988.

qΦs

qχs

Ec

EF

EV

qΦm

ЄF

Metal n-Type s.c.

qΦb

Metal n-Type s.c.

qVbi

Energy-band Diagram before contact Energy-band Diagram after contact

Theory Of MESFET OperationTheory Of MESFET OperationTheory Of MESFET OperationTheory Of MESFET Operation

qΦm = Metal Work Function qΦs = Semiconductor Work Function

qχs = Semiconductor Electron Affinity Reference Energy Level (Vacuum)

Schottky-barrier formed when metal deposited on semiconductor

Ref: Inder Bahl and Prakash Bhartia, Microwave Solid State Circuit Design, A Wiley-Interscience Publication, 1988

Theory Of MESFET OperationTheory Of MESFET OperationTheory Of MESFET OperationTheory Of MESFET Operation

N+ N+

Semi-Insulating Substrate

Depletion Region

Neutral Region

GateSource Drain

n

Ref: http://nina.ecse.rpi.edu/shur/SDM2/Notes/Noteshtm/16MESFET

Theory Of MESFET OperationTheory Of MESFET Operation

S G D

DR

-

• VGS controls channel (DR)• VDS drifts carriers • Fully depleted channel = pinch off condition (Vpinch)

Depletion region forms under schottky contact (gate) and controls the flow of current in the channel (n-type) layer.

Device therefore behaves as voltage controlled switch, capable of very high speed modulation.

Ref: Inder Bahl and Prakash Bhartia, Microwave Solid State Circuit Design, A Wiley-Interscience Publication, 1988

Theory Of MESFET OperationTheory Of MESFET Operation

Ref: Inder Bahl and Prakash Bhartia, Microwave Solid State Circuit Design, A Wiley-Interscience Publication, 1988

Theory Of MESFET OperationTheory Of MESFET Operation

Drain Voltage

Drain Current

VGS = -1

VGS = -0.5

VGS=0

Advantage of SiC MESFET

• Wide Energy Band Gap Device

• High Breakdown Electric Device

• High Electrical and Thermal Conductivity

• High Saturated Electron Velocity

• High Melting Point

• Chemically Inert

Ref: http://www.sec.gov/Archives/edgar/data/895419/0000895419-99-000009.txt

Advantage of SiC MESFET

Ref: http://www.nt.chalmers.se/mve/wbg.htm

SiC Basic MESFET Structure

Source DrainGate

(Schottky)

N+ Epi N+ Epi

N-Channel

P-Buffer

N-type Substrate

Active Layer

High Resistive Substrate

Contact Layer

Ref: http://nina.ecse.rpi.edu/shur/advanced/Notes/Noteshtm/Wide19/sld013.htm

Ref: S.P. Murray and K.P. Roenkar, “An Analytical Model For SiC MESFETs”.

MESFET SpecificationsCree 1 Motorola 2 Sony 3

CRF-20010 MRF9811T1 SGM2014ANSymbol Units SiC MESFET GaAs MESFET GaAs MESFET

General RatingOutput Power Pout dBm 38 21Power Gain G dB 12 14 18Drain Efficiency h

D % 37.5 55

Maximum RatingsDrain-Source Voltage VDSS Vdc 80 10 12

Gate-Source Voltage VGS Vdc -10 -5 -5

Maximum Frequency fmax GHz 20-25 2 2

Total Device Dissipation @ 50 oC PD W 55 0.77 0.1

Operating Junction Temperature TJoC 250 150 125

Off-CharacteristicsGate-Drain Breakdown Voltage V(BR)GDO Vdc 120 15

Drain Saturation Current IDSS Adc 1.8 0.35 0.028

On-CharacteristicsGate Threshold Voltage VGS(th) Vdc -12 -2

Forward Transconductance gfs S 0.15 0.9 0.017

Ref: 1- http://www.cree.com/products/microwave/AppNote_20010_28V-1.0.pdf 2- http://www.mot-sps.com/books/dl110/pdf/mrf9811t1rev0d1.pdf 3- http://www.sel.sony.com/semi/PDF/SGM2014AN.pdf

MESFET Specifications

Comparison of SiC and GaAs MESFET Specifications:• Drain Source Voltage and Drain Saturation Current

– SiC devices have a higher VDSS and a higher IDSS than GaAs devices thereby increasing the power handling capabilities of SiC MESFETs

• Maximum Frequency– SiC fmax is approximately ten times greater than that found

in GaAs devices• Device Power Dissipation

– SiC MESFET thermal dissipation greatly exceeds that of GaAs which allows for greater power handling and higher temperature operation

SiC MESFET Application

The Major Applications Include :

• Wireless Communication

• Microwave Circuits

• High Power

• High Frequency

• Power Amplifiers

Ref: http://www.cree.com

Summary

The Superior Properties of SiC MESFET like higher breakdown voltage, higher thermal conductivity and higher saturated electron velocity makes it one of the most promising devices for high frequency and high power.