Vasantha Pathirana

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.

An Analytical Model for the Lateral Insulated Gate Bipolar Transistor (LIGBT) on Thin SOI

While there are several analytical models dedicated to vertical insulated gate bipolar transistors (IGBTs) there is virtually no reliable model for lateral IGBTs (LIGBTs). LIGBTs are increasingly popular in smart power and power integrated circuits, especially in those applications where high voltage (e.g., 600 V) and high current capability (e.g., 30 A/cm2) are required. In this paper, we report for the first time a complete analytical model for the LIGBT based on semiconductor physics with very few fitting parameters. The model is implemented in the widely available circuit simulator PSpice. The model consistently describes the current and voltage waveforms for all loading conditions. The model is assessed against finite element device simulations and experimental results

Modeling Voltage derivative during inductive turnoff in thin SOI LIGBT

The lateral insulated gate bipolar transistor (IGBT) behavior differs in many aspects from the well-studied vertical IGBT. In this paper, the voltage derivative during inductive turnoff for a silicon-on-insulator (SOI) lateral IGBT (LIGBT) is analyzed in detail. A complete model which accounts for the voltage rise is implemented through an accurate calculation of the equivalent output capacitance. The model is in excellent agreement with two-dimensional simulations and experimental results across a wide range of conditions. Further, the paper shows that previously proposed models, which targeted the vertical IGBT, are not adequate for the description of the turnoff voltage rise in the LIGBT.

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.

Electrothermal model for an SOI-based LIGBT

Several vertical insulated gate bipolar transistor (IGBT) electrothermal models are currently available on circuit simulators. However, no reliable electrothermal models have been proposed for the lateral IGBT (LIGBT). In this paper, for the first time, an electrothermal model for an LIGBT structure based on a novel concept recently reported by Udrea (IEDM, p. 451, 2004), and here termed silicon-on-membrane, is presented. The model relies on a systematic study of both the isothermal and self-heating behaviors of the device. The model is further implemented in the SPICE circuit simulator language and validated against extensive Medici numerical simulations and experimental data

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.

A compact model for thin SOI LIGBTs: description, experimental verification and system application

A complete physical model for the lateral IGBT in thin silicon on insulator technology is presented for the first time. The model is oriented to circuit simulators and is implemented in Pspice. Model results are compared against experimental results and Medici numerical simulations. Numerical convergence performance of the model is verified through the simulation of a half bridge circuit and a complete flyback switch mode power supply.

Flip-chip assembly and 3D stacking of 1000V lateral IGBT (LIGBT) dies

10 A, 1000 V-rated lateral insulated-gate bipolar transistor (LIGBT) has been specifically developed for Implantable Cardioverter Defibrillators (ICDs) and its design optimised for flip-chip assembly. By replacing currently used vertical IGBT with a lateral design which has all terminals on the same side of the die, flip-chip technique could be used for assembly of all components of the ICD. This simplified and lowered the cost of the assembly and enabled advanced embedding and 3D PCB stacking for further product miniaturisation. The ICD product based on lateral IGBTs resulted in 30% smaller footprint and 4 times reduced height compared to existing solutions built with vertical high-voltage devices. Stacking of multiple PCBs assembled with LIGBTs has also been successfully demonstrated, resulting in 70% smaller product footprint compared to solutions based on vertical IGBTs. Moreover, lateral IGBTs have significantly lower leakage currents than vertical devices (>10x), which reduces power consumption during normal operation. This extends the battery life of defibrillators and increases intervals between replacement surgeries, benefitting both the patient and healthcare provider.

A compact steady-state self-heating model for a thin SOI LIGBT

Several vertical IGBT electro-thermal models are currently available on circuit simulators. However, no reliable electro-thermal models have been proposed for the lateral IGBT (LIGBT). In this paper we present a novel steady-state electro-thermal model for a LIGBT on thin Silicon-On-Insulator (SOI) technology. The model is fully-assessed against experimental results and numerical simulations

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.