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

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

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

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

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(?)

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

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

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

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

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

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

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.

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 line @ ~1kV per stage No need to add output from multiple HSM Parallel HSMs 120ohm helical microstrip line @ ~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

Thanks Questions?