Optimization methodologies for power transistors
This PhD-work focuses on optimizing power transistors. These are designed to withstand high voltages and currents, and serve as a key component in present and future consumer compact fluorescent and solid-state lights, as well as in many other (e.g. automotive) electronics. ‘The developed optimized devices in my thesis work are smaller, less expensive, with an almost constant internal electric field, and possess many unique features,’ Boni Boksteen says. ‘Designers and product engineers may find lots of quantitative information, useful for modelling and predicting electronic behaviour for novel future products.’
The main mechanisms responsible for degradation in power transistors, under different stress conditions, are characterized in the work of Boni Boksteen. Also he shows how to identify the location where the stress induces physical and chemical changes.
Boni developed diagnostic techniques and analytical models to predict the transistor’s performance over time. ‘I strongly believed a more quantified approach was possible in this field.’ Boni says. ‘Within NXP Semiconductors I was working as a scientist in the team: experimenting, analyzing and characterizing again and again. This provided me with the opportunity to truly understand the observed phenomena, to generalize optimization techniques and mathematically model device behavior. The latter was mainly performed at the Semiconductor Components (SC) group here at the University of Twente.’
Future demands are quite challenging. Imagine that modern LED lamp devices operate for 35,000 hours: the switches must be able to handle peak-voltages up to 700 volts, and they are not allowed to deteriorate in the off-state, which might lead to ever more leaking currents during their life-time and thus decreased efficiency.
Boni hopes his findings will inspire future designers to come up with proven-robust devices. The work provides necessary insights and in depth electrical characterization of gradient based field-plate assisted power devices. Here a virtually constant internal electric field is obtained according to the RESURF (Reduced Surface Field) principle.
‘Vast theoretical work served as a starting point for my experiments. The scientific literature lacked quantitative information on this topic,’ Boni says. ‘Thorough understanding of the field-plate assisted optimization behaviour even led to a patent for the company. My results also caught attention within the scientific community. I am grateful NXP allowed me to work on generic topics and devices, giving me freedom to not limit myself too narrowly to one or two near-future applications. I was free to work as a scientist within NXP, a position that suits me very well.’
Talking about silicon-based power transistors - and not on popular, more common themes such as those based on Gallium-Nitride (GaN) - Boni was somewhat an odd man on international conferences.
‘The funny thing was, I was addressed for my work even more so, as I talked about the good old proven silicon technologies as I came up with something new there or explained things previously not understood,’ Boni is happy to say. ‘I was pleasantly surprised when, at the IEDM conference in San Francisco, a leading professor from MIT spontaneously came up to me to congratulate me with the work and presentation, asking if I ever considered a future at MIT.’
Yet, when thinking about his future career, Boni tends to search for a job outside a purely academic environment. ‘I like to see the results of my work in the real world one day. The role I played within NXP still appeals to me: aiming at applications starting from an in-depth level of knowledge and understanding. Being of added value to others in this way in my future job, would be great.’