Gianluca Camuso

800V lateral IGBT in bulk Si for low power compact SMPS applications

An 800V rated lateral IGBT for high frequency, low-cost off-line applications has been developed. The LIGBT features a new method of adjusting the bipolar gain, based on a floating N+ stripe in front of the P+ anode/drain region. The floating N+ layer enhances the carrier recombination at the anode/drain side of the drift region resulting in a very significant decrease in the turn-off speed and substantially lower overall losses. Switching speeds as low as 140ns at 25oC and 300ns at 125oC have been achieved with corresponding equivalent Rdson at 125oC below 90mΩ.cm2. A fully operational AC-DC converter using a controller with an integrated LIGBT+depletion mode MOSFET chip has been designed and qualified in plastic SOP8 packages and used in 5W, 65kHz SMPS applications. The device is fabricated in 0.6μm bulk silicon CMOS technology without any additional masking steps.

The Effect of Incomplete Ionization on the Turn-Off Behavior of FS IGBTs

This letter demonstrates for the first time the effect of the incomplete ionization (I.I.) of the transparent p-anode layer on the static and dynamic characteristics of the field-stop insulated gate bipolar transistors (FS IGBTs). This effect needs to be considered in FS IGBTs TCAD modeling to match accurately the device characteristics across a wide range of temperatures. The acceptor ionization energy (EA) governing the I.I. mechanism for the p-anode is extracted via matching the experimental turn-off waveforms and the static performance with Medici simulator.

Avalanche ruggedness of 800V Lateral IGBTs in bulk Si

Avalanche capability of 800V rated Lateral IGBTs (LIGBTs) fabricated using bulk CMOS technology has been investigated for the first time for both turn-on and turn-off. The LIGBTs have been designed for 65kHz operation in energy-efficient, compact off-line power supplies. Measurements of the device during turn-on revealed failures under high line voltages. The device was analysed using a combination of measurements and simulations which revealed that the dynamic avalanche was the cause of failure. An optimised LIGBT has been designed, simulated, fabricated and tested. The optimised device exhibits higher breakdown voltage and improved turn-on avalanche capability. Moreover, the optimised device showed improved avalanche capability during turn-off and reduced likelihood of latch-up.

Modelling of an AlGaN/GaN Schottky diode and extraction of main parameters

This paper describes a method to extract the ideality factor, barrier height and series resistance of a lateral AlGaN/GaN heterostructure power Schottky diode using a simple I-V measurement in on-state and sub-threshold domains. An analytical model previously developed for Gallium Arsenide (GaAs) and Silicon vertical diodes [1] is applied to lateral AlGaN/GaN Schottky diodes and calibrated using extensive experimental results. The validity of the model at increased temperatures (up to 428K) is also investigated and the dependence of the ideality factor and barrier height with temperature are obtained and assessed against those previously reported in the literature [2].

The effect of the collector contact design on the performance and yield of 800V Lateral IGBTs for power ICs

We report here a new physical phenomenon related to contact etch depth in High Voltage Lateral IGBTs (LIGBTs) and propose a design technique to increase yield of LIGBTs in high volume production. We prove for the first time that the contact geometry and placement have direct effect on Collector injection efficiency in LIGBTs. An improved design for 800V LIGBTs obtained by optimising the layout of contact openings is proposed. The new structure resulted in 15% increase in production yield.

Field-stop layer optimization for 1200V FS IGBT operating at 200˚C

This paper is concerned with design considerations for enabling the operation of Field-Stop Insulated Gate Bipolar Transistors (FS IGBTs) at 200 C. It is found that through a careful optimization of the Field-Stop layer doping profile the device has a low leakage current and delivers a favorable tradeoff between the on-state voltage (Von) and turn-off loss (Eoff). An investigation of the adverse effects of increasing the junction temperature on the temperature-dependent properties of the FS IGBTs is also discussed herein.

On the Source of Oscillatory Behaviour during Switching of Power Enhancement Mode GaN HEMTs

With Gallium Nitride (GaN) device technology for power electronics applications being ramped up for volume production, an increasing amount of research is now focused on the performance of GaN power devices in circuits. In this study, an enhancement mode GaN high electron mobility transistor (HEMT) is switched in a clamped inductive switching configuration with the aim of investigating the source of oscillatory effects observed. These arise as a result of the increased switching speed capability of GaN devices compared to their silicon counterparts. The study identifies the two major mechanisms (Miller capacitance charge and parasitic common source inductance) that can lead to ringing behaviour during turn-off and considers the effect of temperature on the latter. Furthermore, the experimental results are backed by SPICE modelling to evaluate the contribution of different circuit components to oscillations. The study concludes with good design techniques that can suppress the effects discussed.

On the vertical leakage of GaN-on-Si lateral transistors and the effect of emission and trap-to-trap-tunneling through the AIN/Si barrier

Vertical leakage in lateral GaN devices has a significant contribution to the overall off-state current at high blocking voltages and high temperatures. It could could lead to premature breakdown before avalanche or dielectric breakdown occur. This paper identifies via experimental results and TCAD simulations the main physical mechanisms responsible for the vertical leakage through the epi and transition layer structure: (i) silicon impact ionization, (ii) electron injection across the AIN nucleation layer/silicon interface, (ill) space charge limited current. In particular, the trap-to-trap model, accounting for the leakage current across the nucleation layer, was implemented showing to be dominant at lower voltages (<200V).

Superjunction IGBT vs. FS IGBT for 200°C operation

Adverse effects on the temperature-dependent properties of Insulated Gate Bipolar Transistors (IGBTs) are often observed when the junction temperature exceeds 175°C. It is believed that attempts in enabling the operation of IGBTs at 200°C will inevitably introduce penalties in some electrical properties of the device. Therefore, the trade-off relationship between the key parameters must be carefully considered. In this paper, we present for the first time that the Superjunction (SJ) IGBT can deliver the best performance trade-offs between the conduction and turn-off losses while maintaining low leakage current at 200°C when compared with other IGBTs. Moreover, the output and switching characteristics of SJ IGBTs depend on the SJ pillar geometry and the doping level of the SJ pillars. We discover that the structure with disconnected p-body and p-pillar with moderate pillar doping concentration (Dpn) is the key in achieving excellent turn-off behavior without sacrificing the on-state voltage drop (Von) at 200°C.

Effect of Bandgap Narrowing on Performance of Modern Power Devices

The effect of the bandgap narrowing (BGN) on performance of power devices is investigated in detail in this paper. The analysis reveals that the change in the energy band structure caused by BGN can strongly affect the conductivity modulation of the bipolar devices resulting in a completely different performance. This is due to the modified injection efficiency under high-level injection conditions. Using a comprehensive analysis of the injection efficiency in a p-n junction, an analytical model for this phenomenon is developed. BGN model tuning has been proved to be essential in accurately predicting the performance of a lateral insulated-gate bipolar transistor (IGBT). Other devices such as p-i-n diodes or punch-through IGBTs are significantly affected by the BGN, while others, such as field-stop IGBTs or power MOSFETs, are only marginally affected.