1. Ultra Fast Hybrid MOSFET/Driver Switch Module R&D for a Broadband Chopper
Tao Tang, Craig Burkhart
Power Conversion Department, SLAC National Accelerator Laboratory

2. Outline Hybrid MOSFET/Driver R&D @ SLAC
Motivation : ILC kicker
Introduction to Hybrid MOSFET/Driver
Proof of Principle Experiments
Future Plan
Hybrid MOSFET/Driver Module for Project X Chopper

3. Motivation : ILC DR Kicker
ILC Damping Ring Kickers Requirement:
±5 kV into 50 Ω
3 ns flattop
~1 ns rise and fall time
Up to 6 MHz burst rate, ~300 pulses, 60Hz repetition rate
Transmission Line Adder Solution:
Commercially available power MOSFETs are not fast enough (3ns minimum switching time)  Hybrid MOSFET/Driver Switching Module (HSM) (~1ns)
Transit time through standard inductive adder limits achievable rise time transmission line adder topology

4. Power MOSFET as Ultra-fast Switch
Power MOSFET has a great potential as switch for pulsed power
Theoretical carrier transit time on the order of 200ps from drain to source
Capable of 1ns switching.
Parasitic packaging inductance slows down the MOSFET
At high frequency, Lg isolates the driver from internal gate electrode
Ls generates negative feed back to MOSFET gate
Ls(dI/dt) voltage reduces VGS
Generates oscillations
Need a damping resistor Rg  impede charge transfer to gate

5. Commercial power MOSFET
Special package/die to minimize parasitic inductance
DEI-475 series MOSFET
IR DirectFET (VDSS<100V)
Integrate driver and MOSFET in same package
Microsemi DRF100/1200
Switching speed ~2-3 ns
Due to Al bonding wire(?)

6. Proof of Principle Experiments: Flip Chip Assembly
Flip chip assembly for minimum inductance
Solder bumpers deposit on MOSFET die
Chip is flipped onto a PCB with conductive epoxy on source and gate connectors
Drain connection is made with copper foil and silver paste
Copper foil for drain
Silver paste
MOSFET die
Solder bumper
Conductive epoxy
PCB traces
PCB D S G S G S D

7. Proof of Principle Experiments: Hybrid MOSFET/Driver circuit
Consists of 4 blocks
Load, Power MOSFET, Totem Pole Driver, Input Buffer
Operate at 1000V into 27 ohm resistive load, output current ~33A
MOSFET
Storage Cap
IXYS driver limits the minimum pulse width. It is not optimized for short pulse width. And it will be improved in the next version.
IXYS Driver
Load Resistors

8. Proof of Principle Experiments: Experiment results
Switching waveform (Vload and Vgate)
VDS=1kV, RLoad=27 ohm, ID=33 A
Fastest switching speed: 1.2 ns
Shortest Pulse from PoP design (FWHM): 7.1 ns
VDS=1kV, RLoad=10 ohm, ID=68 A

9. Proof of Principle Experiments: Transmission line adder
Four Hybrid MOSFET/driver Switching Modules (HSMs)
Four 4.17 m (20 ns) long RG402/U coaxial cables
Four stacked adder PCBs
Matched 200 Ω load

10. Proof of Principle Experiments: Output of the HSMs and Adder
Single HSM
Adder with 4 HSMs
Turn off time: RC limited.
Solution: 1. Inductance
2. Line type structure.
Turn on time ~1.5 ns
Output voltage ~920V
Switching time ~1.4 ns
Output voltage ~3.3kV

11. Proof of Principle Experiments: Summary
PoP design to investigate switching time
Switching 33A into 25ohm in 1.5ns
Conductive Epoxy based flip-chip assembly
Pulse width limited by IXYS driver
Adder design to investigate preservation of switching time
Transmission line adder is capable to combine ultrafast pulses
Long turn off time due to RC recharge of MOSFET

12. Future work Improve HSM design
Assembly method
Use ceramic substrate for thermal handling
Other bonding technique for higher temperature operation
Improve driver design
Get shorter pulse width (replace IXYS driver)
Simplify trigger requirement
High power performance
Recharging
Build adder for ILC parameters. (series and parallel combination of HSMs)
Pulse width is not a consideration for existing experiments. It will be a focus for next version of HSM.

13. Project X Chopper Requirement
Bunch spacing: 6.15ns (162.5MHz)  Pulse width <6.15ns, Flat top ~1.5ns
Optimize driver to reduce minimum pulse width (ILC: 5ns PW, 3ns Flat top)
Chopper structure:
25ohm transmission ~1kV per stage
No need to add output from multiple HSM
Parallel HSMs
120ohm helical microstrip ~200V
Optimize turn off of HSM
Smaller MOSFET die
~94MHz average PRF (6MHz for ILC)
Heat dissipation 5.9kW per switch unit (1kV into 25 ohm)
1.8kW (Switching)+0.5kW(Rds)+3.6kW(Coss)=5.9kW
408W for TO247 package (same die), 1.8kW for IXYS DE475 MOSET  800W per HSM
High speed trigger of HSM
Power handling of Al2O3 substrate hybrid  Number of HSM required

14. Thanks
Questions?