Microwave Solid State Power Devices Yonglai Tian

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Microwave Solid State Power DevicesYonglai Tian
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• 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

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Various types of microwave power devices
Magnetron
Traveling wave tube
Gyrotrons
Klystron
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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
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Multiple DoD platform will benefit from microwave
solid state devices and WBG semiconductors
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Electrodeless HID lamps driven by microwaves
200w aperture HID lamps (7mm) driven by solid
state microwave devices
1400w magnetron driven HID lamps,
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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)

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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)

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• 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

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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
• Vmax Voltage breakdown
• Current density limited by bandgap and thermal
  conductivity

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Performance characterization

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

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Widely used Si microwave devices

• A typical Si BJT characteristics
• Frequency 2.7-2.9 GHz
• Output power 105 W
• Pulse width 50 mm
• Duty cycle 10
• Gain 6.5 db (min)
• Efficiency 40 (min)
• Supply voltage 40V

• Si BJT
• lt 5 GHz
• 100-600W at 1 GHz
• gt 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

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GaAs MESFET (Metal semiconductor field effect
transistors)

• GaAs MSFET
• 3-30 GHz
• Power density 0.5-0.8 w/mm
• Power level and cost
• Frequency band Power (W) cost ()
• C and S 10 300
  20 600 30 900
• Ku 10 1000 15
  1500
• Limitation
• f and Pmax gate length, thermal conductivity

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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

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State of the art power output performance
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State of the art power density performance
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State of the art PAE performance
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Evolution of microwave device noise figures
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• 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

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Advantages of wide bandgap semiconductors(SiC,
GaN and diamond)

• Wide bandgap
• 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

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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

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Advantages

• 3. High thermal conductivity
• 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

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Physical characteristics of Si, GaAs and main
wide bandgap semiconductors
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WBG semiconductor material challenges
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• 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

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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),
  1987 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

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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 2000-2300oC
• DT of 10-30C controlled by moving RF coil
• Growth rate controlled by DT and pressure in
  reactor

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Defects in SiC wafer

• Micropipes breakdown at low voltage
• Dislocations
• Low angle grain boundaries
• Stacking faults

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GMU WBGS research projectsIon 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.

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N-implanted SiC (50 KeV to 4MeV at 700oC)
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B-implanted SiC (50 KeV to 4MeV at 700oC)
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Multiple energy P-implanted SiC
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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.

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RSB spectra on N-implanted SiC
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Sheet resistivity of annealed SiC wafersGMU data
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• 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.
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Best Reported Sheet Resistivity of Ion Implanted
SiC
. Figure 2. Sheet resistivity of Al implants
into 6H silicon carbide at room tmperature
Figure 1. Sheet resistivity of nitrogen implants
into 6H silicon carbide at room tmperature
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• 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

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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

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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
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• 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..
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High power SiC MESFET

• Three epitaxial layers
• P buffer layer
• Channel layer doped Nd3x1017cm-3
• Heavily doped n cap layer
• Performance
• Pmax 15W
• Frequency 2.1 Ghz
• Power density 1w/mm
• PAE 54

a
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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
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• 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

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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

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