October 3-5, 2016 International Workshop on Power Supply On Chip (PwrSoC 2016) Monolithic integration of GaN power transistors integrated with gate drivers October 4, 2016 Tatsuo Morita Automotive & Industrial Systems Company Panasonic Corporation
Potential Application for WBG semiconductors GaN power transistors are suited for high-frequency applications. Production Normally-off GaN Gate Injection Transistor (GaN-GIT) 600V/15A TO-220 600V/15A SMD Proto-type 30V normally-off GaN-GITs (developed in 2014)
Advantages of GaN for Power device GaN inherently has superior material properties for Power switching device Unique feature of GaN is 2-Dimensional Electron Gas(2DEG) which serves both high electron density and high electron mobility Maximum Electric Field (MV/cm) Comparison of material properties Bandgap (ev) 3 2 1 Si GaN SiC Electron Mobility (cm 2 /Vs) AlGaN/GaN Hetero-junction FET Source Gate Un-doped AlGaN Drain 2DEG channel Un-doped GaN Super-lattice Buffer Si substrate Saturation drift velocity x10 7 (cm/s) Baliga s FOM High sheet carrier density induced by polarization effects at the AlGaN/GaN hetero-interface without any doping GaN-FET can be fabricated on costeffective Si-substrates Normally-on operation
Normally-off GaN Gate Injection Transistors - GIT - Gate Injection Transistor (GIT) Recovery characteristics Normally-off operation Vg=0V: p-algan lifts up the potential at the channel. Vg>Vf: Hole injectction Electron generation Large Drain current Very low RonQg RonQg of 600V GIT is 0.7 WnC which is 1/13 of that of the latest SJ-MOSFET. Good Recovery characteritics GIT can be operated as a free-wheeling diode with very small charging current.
Power supply Power converter have progressed with overcoming design trade-off among power density and efficiency, cost. To make more advanced, GaN-FETs have been actively investigated. AC 100-230V PFC GaN power devices used in Power supply AC-DC Power Supply Isolated DC-DC converter DC12V Bus Today s topic Non-isolated DC-DC converter 1~ 1.2V CPU Totem-pole PFC using GITs reported by Panasonic on PCIM2014 1MHz resonant converter using 600V normally-off GaNs reported by Fraunhofer ISE on ECSCRM2012 5MHz/50A GaN POL converter reported on PCIM2014 GaN POL power IC integrated with gate drivers reported on ISPSD14
Size (mm 2 ) For smaller POL converter Increasing frequency greatly helps to reduce the system size. Low RonQg power device and low parasitic inductance are key factors. Advantage by increasing frequency Si-MOS Module Inductor 350nH Compact 600 500 400 300 200 100 0 GaN Module Inductor 170nH GaN 70nH 1 2 5 Frequency (MHz)
30V-class normally-off GaN-GITs RonQg of developed 30V GaN-GIT is reached to 19.1mΩnC *1. -> 36% smaller than that of reported Si-MOSFET *2. *1 H. Umeda, et al., PCIM2014 *2 S. Xu, et al., International Electron Devices Meeting (IEDM) Technical Digests, 145(2009)
Impact of the parasitic inductance Parastic inductance on power loop (L Power_Loop ) increase the spike voltage It limits di/dt and causes gate oscillation, increase noise. Parastic inductance on gate loop (L Gate_Loop ) increase the gate charging time. Parasitic inductance on Power Loop L Power_Loop C out Spike voltage V DS I DS V Spike L Power _ Loop I t DS limit di/dt to keep Vds under BVds causes gate oscillation generate Noise Parasitic inductance on Gate Loop L Gate_Loop Reduction of Lgate_Loop also effectively increase gate charging speed
This Work : GaN-based IC with gate driver GaN transistors and GaN gate drivers are integrated to a compact chip Conventional Inductor (L) High-side Transistor (Hi) Capacitor (C) This Work Si-based Gate Drivers Low-side Transistor (Lo) One Chip GaN-based IC
Voltage (V) Impact of Integration : Small Parasitic Inductances Switching speed is increased by reduction of parasitic inductances V gate driver Gate Drivers Simulated turn-on switching waveform L1 L2 L3 L4 Parasitic Inductors Vin GaN Transistors L Vout C 14 12 10 8 6 4 2 0-2 -4 L1~L4 = 1nH 15.8V/ns L1~L4 = 4.5nH 12.5V/ns 0 1 2 3 Time (ns) 12V 1.8V Iout = 6A 2MHz operation
Operation Loss (W) Operation Loss (W) Impact of Integration : Small Parasitic Inductances Operation loss is reduced by the reduction of parasitic inductances. 1.3 1.2 12V 1.8V 1.1 1 1 0.9 0.8 0.7 Simulated operation loss Iout=6A @ 2MHz L1+L2 (L3=L4=0) L3+L4 (L1=L2=0) 0.6 2 4 6 8 10 12 0 Parasitic Inductance (nh) 2 4 6 8 10 12 Parasitic Inductance (nh)
GaN Gate Driver : DCFL (Direct Coupled FET Logic) High power consumption in GaN gate driver of DCFL. Circuit Design Time Chart Iin DCFL Large Wg Switching Power Device VG 5V D-Tr. Charge Current Vout tr tf VG E-Tr.1 E-Tr.4 Vout Iin High Short-Circuit Current Short-Circuit Current Flowing
GaN Gate Driver : DCFL with Buffer Amplifier Low power consumption in GaN gate driver by buffer amplifier. Circuit Design Time Chart DCFL Buffer Amplifier Iin Small Wg Large Wg Switching Power Device VG 5V VG D-Tr. E-Tr.1 E-Tr.2 E-Tr.3 E-Tr.4 Vout Vout tr tf Iin Low High Short-Circuit Current Short-Circuit Current Flowing
GaN Device Structure and Characteritics Ids Ids (A/mm) Ron Ron (Ωmm) D-mode HFET and E-mode GIT are monolithically fabricated. Device Structure Device Characteristics GaN-GIT Gate GaN-HFET Schottky Gate S D S AlGaN D p-algan GaN Buffer layer Isolation layer Si Substrate 1E+2 1E+0 1E-2 1E-4 1E-6 1E-8 HFET HFET 1E-10-4 -2 0 2 4 6 8-4 -2 0 Vgs (V) GIT GIT 2 4 6 8 30 25 25 20 15 10 10 5 0 0
Operation Characteristics of GaN Gate Driver Voltage (V) GaN gate driver is about 40% faster than Si gate driver. 6 5 Vin tr=7ns tf=5ns C load :1500pF 4 3 2 1 0 Vout -1-2 Pulth Width:50ns -2-50 0 50 100-50 0 50 100 time (ns)
Power Power Consumption of of Gate Driver [W] (W) Low Consumption of GaN Gate Driver Power consumption is reduced about 98.5% by using GaN DCFL with buffer amplifier. 10 9 8 7 6 5 4 3 2 1 0 Without buffer amplifier 98.5% Reduction With buffer amplifier 0 20 40 60 80 100 duty duty (%) [%] High t1 duty ratio = t1 / t2 Low t2 Gate Driver Output Voltage
GaN-based DC-DC Converter IC Chip photograph Gate Driver for High side High side Transistor Module layout with GaN-based IC Driver High-GIT Driver Low-GIT Inductor Gate Driver Low side Transistor for Low side 1mm Circuit diagram Integration GaN-based IC Inductor Compact chip size is 5.1mm x 2.3mm GaN-based IC reduces the system size
Operating Efficiencies of DC-DC Converter Efficiency (%) Peak efficiency of 88.2% is achieved with 12V - 1.8V DC- DC conversion at 2MHz 95 90 85 80 12V 1.8V DCDC down conversion 1MHz 2MHz 3MHz 75 70 0 2 4 6 8 10 12 Load Current (A) This work Discrete
Operation Loss (W) Analyzed operating loss of GaN-based IC Efficiency (%) Switching loss have been reduced 15% by using GaN-based DC- DC converter IC. 2.5 90 2 87.8% 88.2% 88 12V 1.8V, Iout=6A, @2MHz 1.5 86 1 84 0.5 0 0.80W 0.68W 1 2 Discrete This Work 82 80 Switching Loss Eoss Conduction Loss
Summary Compact GaN-based DC-DC Converter IC with High Speed Gate Drivers for Highly Efficient DC-DC Converters GaN Gate Driver GaN-based IC DCFL with buffer amplifier Monolithically fabrication of HFET and GIT High speed switching (tr + tf = 12ns) 5.1mm X 2.3mm Compact chip size Peak Efficiency (12V-1.8V) : 88.2%@2MHz This work is partially supported by the New Energy and Industrial Technology Development Organization (NEDO), Japan, under the Strategic Development of Energy Conservation Technology Project.