Ranbir Singh

Cryogenic Operation of Silicon Power Devices

List of Figures. List of Tables. Foreword. Preface. 1. Introduction. 2. Temperature Dependence of Silicon Properties. 3. Schottky Barrier Diodes. 4. P-I-N Diode. 5. Power Bipolar Transistors. 6. Power MOSFETs. 7. Insulated Gate Bipolar Transistors. 8. Power Junction Field Effect Transistors. 9. Asymmetric Field Controlled Thyristors. 10. Thyristors. 11. Synopsis. References. Index.

Analysis and optimization of power MOSFETs for cryogenic operation

Abstract Detailed experimentally measured data taken between 300 and 77 K is presented for power DMOSFETs with a wide range of breakdown voltages. The breakdown voltage and on-resistance were found to decrease whereas the threshold voltage and transconductance were found to increase with a decrease in operating temperature. This paper provides analytical models for the behavior of these parameters. Using these models, a relationship between the ideal specific on-resistance and the breakdown voltage of silicon power MOSFETs at cryogenic temperatures has been developed for the first time. In addition, the optimal cell design of a power DMOSFET has been shown to change as the operating temperature goes from 300 to 77 K due to the differences between the temperature dependence of inversion, accumulation and bulk mobilities.

Power MOSFET analysis/optimization for cryogenic operation including the effect of degradation in breakdown voltage

Detailed experimental data taken between 300 and 77 K is presented for power DMOSFETs. The breakdown voltage and on-resistance were found to decrease whereas the threshold voltage and transconductance were found to increase with a decrease in operating temperature. This paper provides andytical models for the behaviour of these parameters. Using these models, a relationship between the ideal specific on resistance and the breakdown voltage of silicon power MOSFETs at cryogenic temperatures has been developed for the first time. In addition, the optimal cell design of a power DMOSFET has been shown to change as the operating temperature goes from 300 to 7% due to differences between the temperature dependence of inversion, accumulation and bulk mobilities.

Cryogenic operation of PiN power rectifiers

Abstract The results of detailed measurements and modeling on 1200 V P - i - N diodes over a temperature range of 300-77 K are presented in this paper. At typical rated current levels, the forward voltage drop increases with a decrease in temperature. Analysis and measurements prove that there is an order of magnitude reduction in the i -region stored charge from 300 to 77 K. This results in greatly reduced switching losses at 77 K. An analytical model, including end region recombination with bandgap narrowing, is presented to explain the experimental observations.

10 kV SiC BJTs — Static, switching and reliability characteristics

Open-base breakdown voltages as high as 10.5 kV (91% of theoretical avalanche limit and 125 V/μm), on-resistance of 110 mΩ-cm2 close to the unipolar limit of 94 mΩ-cm2, and current gain as high as 75 are measured on 10 kV-class SiC BJTs. Monolithic Darlington-connected BJTs fabricated on the same wafer yield current gains as high as 3400, and show Si BJT-like output characteristics with a differential on-resistance as low as 44 mΩ-cm2 in the saturation region and a distinct quasi-saturation region. Switching measurements performed at a DC link voltage of 5 kV and collector current of 8 A feature a collector current rise time as low as 30 ns during turn-on and collector voltage recovery time as low as 100 ns during turn-off. Very low turn-on and turn-off switching energies of 4.2 mJ and 1.6 mJ, respectively, are extracted from the switching transients, which are 19 and 25 times smaller than the corresponding switching energies reported on 6.5 kV Si IGBTs. When turnedon to a short-circuited load at a collector bias of 4500 V, the 10 kV BJT shows a temperature-invariant, withstand time in excess of 20 μs. Leakage currents <; 1μA (system limit) are measured, even after 234 hours of operation under a DC collector bias of 5000 V at elevated temperatures.

Cryogenic operation of asymmetric N-channel IGBTs

Detailed experimental data taken for asymmetric nchannel IGBTs between 300 and 77K are presented. The forward voltage drop, the gain of the inherent PNP transistor and turn off time were found to decrease whereas the threshold voltage and transconductance were found to increase with a decrease in operating temperature. This paper provides analytical models for the behaviour of these parameters. A much lower on-state and switching power loss is predicted for IGBTs operated at cryogenic temperatures.

Rapidly Maturing SiC Junction Transistors Featuring Current Gain (β) > 130, Blocking Voltages up to 2700 V and Stable Long-Term Operation

SiC npn Junction Transistors (SJTs) with current gains as high as 132, low on-resistance of 4 mΩ-cm2, and minimal emitter-size effect are demonstrated with blocking voltages > 600 V. 2400 V-class SJTs feature blocking voltages as high as 2700 V combined with on-resistance as low as 5.5 mΩ-cm2. A significant improvement in the current gain stability under long-term high current stress is achieved for the SJTs fabricated by the high gain process.

Cryogenic operation of power bipolar transistors

The results of detailed measurements, simulations and modeling on 500 V, 4 Amps NPN BJTs are reported in the 300-77 K temperature range. For these devices, as the operating temperature is reduced from 300 to 77 K, the current gain has been found to decrease by more than an order of magnitude; the on-state collector-emitter and base-emitter voltages increase by 40 and 80% respectively; although the collector-base breakdown decreases by about 20%, the collector-emitter breakdown increases by about 20%, and the storage and fall times reduce by 10/spl times/ and 6/spl times/, respectively. Through numerical simulations it is shown that the emitter current crowding is much more severe at 77 K than at 300 K. Using verified analytical models and established optimization techniques, it is shown that a 77 K optimally designed BJT has a lower emitter, base and collector dopings and a larger emitter area than a similarly rated 300 K optimized device.

15 kV SiC PiN diodes achieve 95% of avalanche limit and stable long-term operation

This paper reports on ultra-high voltage, >15 kV SiC PiN rectifiers exhibiting >95% of the avalanche rating and 115 V/μm. This is one of a few reports on > 15 kV blocking voltages measured on any single semiconductor device, and the highest percentage of the avalanche limit ever reported on devices fabricated on > 100 μm thick SiC epilayers. Excellent stability of on-state voltage drop (VF) is displayed by 5.76 mm2 and large-area, 41 mm2 PiN rectifiers, when continually biased at high current densities for several days. The impact of carrier lifetime on the device performance for SiC bipolar devices with ultra-thick (≥100 μm) base layers is investigated by comparing I-V-T characteristics of SiC PiN rectifiers fabricated on 100 μm and 130 μm thick epilayers.

Fulfilling the Promise of High-Temperature Operation with Silicon Carbide Devices: Eliminating bulky thermal-management systems with SJTs

Electronics operating at high temperatures are expected to revolutionize key industries in ways not yet imagined. It will allow aerospace engine applications, actuators and downhole electronics, and vehicle power systems to be squeezed into significantly smaller spaces through reduction or elimination of bulky thermal-management systems. Silicon carbide (SiC) offers great potential for the realization of high-temperature power devices because of its attractive electrical properties, such as wide bandgap, high breakdown electric field, and high thermal conductivity. However, many device structures in SiC are not suitable for use at high temperatures because they are not able to fully exploit these properties to deliver lowleakage currents and superior long-term reliability. In contrast, SiC junction transistors (SJTs) and optimized junction barrier Schottky (JBS) rectifiers have now been demonstrated with superior high-temperature performance due to their intrinsic advantages stemming from these device structures. This article surveys important physical phenomenon that limit high-temperature operation of SiC power devices, and presents experimental results from GeneSiC of higher temperature SiC power device operation.