1. Microwave Solid State Power Devices Yonglai Tian

2. Introduction of microwave power devices
Performance of Si and GaAs microwave devices
Wide bandgap semiconductors for microwave applications
Processing of WBG silicon carbide wafers
SiC microwave power devices
GaN microwave power device

4. Various types of microwave power devices
Magnetron
Traveling wave tube
Gyrotrons
Klystron

5. Disadvantages Large size Heavy Fixed frequency
Complicated power supply (HV)
Poor quality of waveform spectrum
Slow tuning and coupling
Cost
Single mode cavity for Microwave sintering of advanced ceramics

6. Multiple DoD platform will benefit from microwave solid state devices and WBG semiconductors

7. Electrodeless HID lamps driven by microwaves
200w aperture HID lamps (7mm) driven by solid state microwave devices
1400w magnetron driven HID lamps,

8. Various types of microwave solid state devices
Bipolar Junction Transistors (BJT)
Si BJT
HBT (hetero junction bipolar transistor)
AlGaAs-GaAs HBT
SiGe-Si HBT
Field Effect Transistors
GaAs MESFET (metal-semiconductor field effect transistors)
HEMT (high electron mobility transistors)

9. Various types of microwave solid state devices
Wide Bandgap Transistors
SiC
SIT (static induction transistors)
MESFET (metal-semiconductor field effect transistors)
HBT (hetero junction bipolar transistor)
GaN
HEMT (high electron mobility transistors)

10. Introduction of microwave power devices
Performance of Si and GaAs microwave devices
Wide bandgap semiconductors for microwave applications
Processing of WBG silicon carbide wafers
SiC microwave power devices
GaN microwave power device

11. Performance characterization
Out put power Pmax
Pmax a Vmax x Imax
Vmax: Voltage breakdown
Imax: Heat removed, gate width and length
Power Density PD
PD = Vmax x Current density
Current density: limited by bandgap and thermal conductivity

12. Performance characterization
Frequency
f max a (Vs/L)
Vs. saturated carrier velocity
Gate length
Pma α 1/f2
Efficiency PAE
Depends on wave shape, impedance, leakage current and power gain

13. Widely used Si microwave devices
A typical Si BJT characteristics
Frequency; GHz
Output power: 105 W
Pulse width: 50 mm
Duty cycle: 10%
Gain: db (min)
Efficiency: 40% (min)
Supply voltage: 40V
Si BJT
< 5 GHz
W at 1 GHz
> 40% Efficiency
Low cost
Limitation:
Pmax: voltage breakdown and current (limited by emitter periphery and resistivity of epitaxial layer)
f : limited by carrier mobility,
capacitance C bc

14. GaAs MESFET (Metal semiconductor field effect transistors)
GaAs MSFET
3-30 GHz
Power density: w/mm
Power level and cost:
Frequency band Power (W) cost ($)
C and S Ku
Limitation:
f and Pmax: gate length, thermal conductivity

15. HEMT and HBT HEMT (High electronic mobility transistor)
AlGaAs-GaAs heterojunction
5-100 GHz
High frequency
High Pmax
High efficiency
Low noise
HBT (heterojunction bipolar junction transistor)
Similar to BJT, but much higher power and frequency performance

16. State of the art power output performance

17. State of the art power density performance

18. State of the art PAE performance

19. Evolution of microwave device noise figures

20. Introduction of microwave power devices
Performance of Si and GaAs microwave devices
Wide bandgap semiconductors for microwave applications
Processing of WBG silicon carbide wafers
SiC microwave power devices
GaN microwave power device

25. Advantages of wide bandgap semiconductors (SiC, GaN and diamond)
SiC: 3.2 eV
GaN: 3.4 eV
Si : 1.1 eV
GaAs: 1.4 eV
3 times higher than that of Si and GaAs
High service temperature of 650 oC due to the high intrinsic temperature
Low noise

26. Advantages High breakdown voltage
SiC: 10 times higher than that of Si and GaAs
High output power due to high V
High operating frequency
Short-channel MESFETs in SiC
Fmax : 50 GHz

27. Advantages 3. High thermal conductivity High Saturated velocity
SiC 4.9 w/(C-cm)
10 times higher than that of Si and GaAs
Si: 1.6 w/(C-cm)
GaN 0.5 w/(C-cm)
High Saturated velocity
SiC 2.2 x107 m/s
2 times higher than that of Si and GaAs
Si and GaAs: 1 x107 m/s

28. Physical characteristics of Si, GaAs and main wide bandgap semiconductors

31. WBG semiconductor material challenges

32. Introduction of microwave power devices
Performance of Si and GaAs microwave devices
Wide bandgap semiconductors for microwave applications
Processing of WBG silicon carbide wafers
SiC microwave power devices
GaN microwave power device

33. Growth of SiC single crystal
J. A. Lely , Philips Labs 1955 sublimation process for growing a-SiC crystals
Davis at North Carolina State University (NCSU), seeded-growth sublimation process
Cree Res, started in 1987 by students from the NCSU.
Cree, 1990, Introduction of 25 mm single crystal wafers of 6H-SiC 1990

34. Physical vapor transport (PVT) growth of SiC single crystal wafers
PVT growth process:
Evaporation of SiC charge materials
Transport of vapor spices to the growth surface
Adsorption surface diffusion and incorporation of atoms into crystal.
Temperature: oC
DT of 10-30C controlled by moving RF coil
Growth rate controlled by DT and pressure in reactor

35. Defects in SiC wafer Micropipes– breakdown at low voltage Dislocations
Low angle grain boundaries
Stacking faults

37. GMU WBGS research projects: Ion implantation of SiC wafers
Ion implantation is the only viable selective area doping techniques for SiC device production
N and P were implanted in p-type and Al and B were implanted in n-type 6H-SiC using single and multiple ion energy schedules ranged from 50 KeV to 4 MeV
Second ion mass spectrometry measurements (SIMS) were conducted to obtain the implant depth profiles
Doping layer theickness.

38. N-implanted SiC (50 KeV to 4MeV at 700oC)

39. B-implanted SiC (50 KeV to 4MeV at 700oC)

40. Multiple energy P-implanted SiC

41. Rapid annealing of ion implanted SiC
The crystal lattice is damaged by the penetration of ion energetic ions
Post annealing is necessary to recover the lattice damage
Microwave and conventional annealing at 1500C
Microwave: Heating rate; 200oC/min, total time: 20 min.
Conventional: heating rate: 10oC/min, total time 3 hr.
Rutherford backscattering (RBS) measurements are conducted before and after ion-implantation to study the recovery of the crystal lattice.

42. RSB spectra on N-implanted SiC

43. Sheet resistivity of annealed SiC wafers GMU data

44. Sheet resistivity of nitrogen-implanted 4H-SiC as a function of time and temperature.
Sheet resistivity of phosphorus -implanted 4H-SiC as a function of time and temperature.

45. Best Reported Sheet Resistivity of Ion Implanted SiC
Figure 1. Sheet resistivity of nitrogen implants into 6H silicon carbide at room tmperature
. Figure 2. Sheet resistivity of Al implants into 6H silicon carbide at room tmperature

46. Introduction of microwave power devices
Performance of Si and GaAs microwave devices
Wide bandgap semiconductors for microwave applications
Processing of WBG silicon carbide wafers
SiC microwave power devices
GaN microwave power device

47. SiC microwave power devices
High power 4H-SiC static induction transistors (SITs)
Vertical short channel FET structure
Current flow vertically by modulating the internal potential of the channel using surrounding gate structure
Characteristics similar to a vacuum-tube tiode
470W (1.36 /mm) at 600 MHz
38 W (1.2 w/mm) at 3 GHz
PAE ~ 47%

48. High power 4H-SiC static induction transistors (SITs)
Cross section of a SiC SIT
SEM photo of a SIT device. The mesa fingers are 1 µm wide and 100 µm long. The total mesa length is 1 cm (100 fingers).
Measured static I-V characteristics of a SIT

49. The best performance
High output power; 900 W (at 1.3 GHz, drain efficiency = 65%, gain = 11 dB) [Northrop-Grumman/ Cree Inc]
High frequency performance with a cut-off frequency of 7 GHz [Purdue]
A comparison of SIT with other relevant SiC microwave devices..

50. High power SiC MESFET Three epitaxial layers Performance
P buffer layer
Channel layer doped Nd=3x1017cm-3
Heavily doped n+ cap layer
Performance
Pmax : 15W
Frequency: 2.1 Ghz
Power density: 1w/mm
PAE; 54% a

52. Cross section of SiC MESFET
Cross section of SiC MESFET. The epitaxial layers were grown on a semi-insulating SiC substrate, including p-buffer layer and a n-doped channel layer

54. Introduction of microwave power devices
Performance of Si and GaAs microwave devices
Wide bandgap semiconductors for microwave applications
Processing of WBG silicon carbide wafers
SiC microwave power devices
GaN microwave power device

55. GaN Power High electronic mobility transistors
two dimensional electron gas with a high mobility is formed at the AlGaN-GaN heterojunction interface, the mobility can be in excess of 1000 cm2/Vs
High frequency 100GHz
High power density: 10w/mm
Base station microwave power amplifier
highly linear mixers
high power switches