Performance comparison of wide bandgap semiconductor rf power devices

Impressive radio frequency power performance has been demonstrated by three radically different wide bandgap semiconductor power devices, SiC metal semiconductor field effect transistors (MESFETs), SiC static induction transistors (SITs), and AlGaN heterojunction field effect transistors (HFETs). AlGaN HFETs have achieved the highest f_max of 97 GHz. 4H-SiC MESFETs have achieved the highest power densities, 3.3 W/mm at 850 MHz (CW) and at 10 GHz (pulsed). 4H-SiC SITs have achieved the highest output power, 450 W (pulsed) at 600 MHz and 38 W (pulsed) at 3 GHz. Moreover, a one kilowatt, 600 MHz SiC power module containing four multi-cell SITs with a total source periphery of 94.5 cm has been demonstrated.     

An assessment of wide bandgap semiconductors for power devices

An advantage for some wide bandgap materials, that is often overlooked, is that the thermal coefficient of expansion (CTE) is better matched to the ceramics in use for packaging technology. It is shown that the optimal choice for uni-polar devices is clearly GaN. It is further shown that the future optimal choice for bipolar devices is C (diamond) owing to the large bandgap, high thermal conductivity, and large electron and hole mobilities. A new expression relating the critical electric field for breakdown in abrupt junctions to the material bandgap energy is derived and is further used to derive new expressions for specific on-resistance in power semiconductor devices. These new expressions are compared to the previous literature and the efficacy of specific power devices, such as heterojunction MOSFETs, using GaN are discussed.     

Wide bandgap semiconductor materials and devices

Given a matrix of all semiconductor materials and their properties, the highest and the lowest of these property values will almost always be associated with wide bandgap materials. The many possible combinations of these “poles and zeros” lead not only to superlative electron device performance, but to new device concepts as well. An overview of wide bandgap semiconductor properties is presented followed by several concepts for both new and enhanced devices. Finally, impediments to immediate exploitation and a time-oriented appraisal of the various materials and devices is presented     

Impact of wide bandgap microwave devices on DoD systems

Radiofrequency (RF) semiconductor electronics enable military systems that operate in the microwave and millimeter wave frequency bands of 1-100 GHz. The performance of numerous electromagnetic systems could be enhanced by the inclusion of wide bandgap (WBG) microwave and millimeter wave devices, either as power amplifier or receiver elements. The demonstrated power performance has generally been six to ten times that of equivalent gallium arsenide or indium phosphide devices up through 20 GHz, with enhanced dynamic range and improved impedance matching. These characteristics provide an opportunity to significantly reduce the number of modules required for many active aperture antenna systems, hence, cost, while enabling new capabilities for shared apertures. Prior to realization of any WBG system deployment, however considerable development and maturation of WBG materials, devices, and circuits must yet ensue.     

Trends in power semiconductor devices

This paper reviews recent trends in power semiconductor device technology that are leading to improvements in power losses for power electronic systems. In the case of low voltage (<100 V) power rectifiers, the silicon P-i-N rectifier has been displaced by the silicon Schottky rectifier, and it is projected that the silicon TMBS rectifier will be the preferred choice in the future. In the case of high voltage (>100 V) power rectifiers, the silicon P-i-N rectifier continues to dominate but significant improvements are expected by the introduction of the silicon MPS rectifier followed by the GaAs and SiC based Schottky rectifiers. Equally important developments are occurring in power switch technology. The silicon bipolar power transistor has been displaced by silicon power MOSFETs in low voltage (<100 V) systems and by the silicon IGBTs in high voltage (>100 V) systems. The process technology for these MOS-gated devices has shifted from V-MOS in the early 1970s to DMOS in the 1980s, with more recent introduction of the UMOS technology in the 1990s. For the very high power systems, the thyristor and GTO continue to dominate, but significant effort is underway to develop MOS-gated thyristors (MCTs, ESTs, DG-BRTs) to replace them before the turn of the century. Beyond that time frame, it is projected that silicon carbide based switches will begin to displace these silicon devices     

Challenges and potential payoff for crystalline oxides in wide bandgap semiconductor technology

While growth of wide bandgap semiconductor materials on crystalline oxides (sapphire, lithium gallate, lithium aluminate, zinc oxide and others) has become routine, growth of crystalline oxides on wide bandgap materials remains challenging and minimally explored. The potential payoff in terms of enhanced device performance, increased functionality and reliability warrants examining this option. This presentation aims at targeting key areas, where crystalline oxides could improve wide bandgap semiconductor device performance. Some of these include the use of ferroelectric oxides for power switching applications, oxides with anisotropic dielectric constants for high voltage termination and oxides with large electric flux density near breakdown. Unique polarization engineered structures are described that are enabled by using lithographically defined poled regions in a ferroelectric substrate. The desired crystalline oxide properties, potential implementation challenges and potential pitfalls will be discussed.     

Thermal feedback in power semiconductor devices

Thermal feedback (TF) is an important aspect for the thermal management of semiconductor devices and high-power density integrated circuits. Different features of positive and negative TF in transistors are reviewed and summarized for the macroscopic domain. The thermal feedback mechanism is applied to the microscopic domain of noise fluctuations in semiconductor devices. It is argued that TF may be responsible for a major part of 1/fflicker or excess noise. Some experimental evidence is presented which supports this thermal feedback 1/f-noise theory for bipolar and MOS field effect transistors. Device and circuit design rules for the minimization of transmitter noise are given.     

功率半导体器件的发展和市场

功率半导体器件的全球销售额每年以约１５％的速率增长,而传统器件如ＳＣＲ和ＧＴＲ等的年增长率远小于新型器件。以Ｓｍａｒｔ Ｐｏｗｅｒ为代表的新型功率器件集功率、控制和信息于一体,是今后发展的重点。     

Studies of turn-off effects in power semiconductor devices

An analytical model has been developed for analyzing current and voltage transients during high power diode recovery. Using the charge control approach and approximating the excess charge distribution by simple geometrical curves a fast and convenient method for computer analysis is obtained. The model is thoroughly physical and makes use of the proper diode design parameters and the differential equations of the electrical network. There is no need for any experimental fitting parameter. All relevant complicating effects as emitter recombination, nonabrupt pn-junction and reverse current influence on the space-charge layer are considered. Comparisons between calculated and measured recovery behavior under several different conditions show good agreement and prove that the model may serve as a useful tool in device and circuit development including RC-snubber design. Furthermore, the calculated charge distribution varies during the recovery in a physically reasonable manner. Starting from measured recovery transients this model may also be used as a new method for determining the excess charge content in the diode at the beginning of the recovery phase.     

Progress in wide bandgap technology

The developing list of wide gap substrates for device production is remarkable compared with a few years ago and continues to provide new device design possibilities. For GaN it ranges from the largest volume (and hetero) materials, sapphire and SiC (both available in 2″–4″ diameters and used for commercial devices) to homo and hetero substrates that now include four compound materials; aluminium nitride (AIN), gallium nitride (GaN), silicon carbide (SiC), and zinc oxide (ZnO). These are all available commercially, but in varying stages of size, unit volumes, surface and defect qualities. Additionally, a fifth substrate has been announced in the form of HVPE-grown aluminium gallium nitride (AlGaN) available in development quantities. Their production processes include several types of vapiur phase epitaxy, vapour phase transport, crystallisation from the melt and solution growth. Since they are all wide gap materials, these production methods are all high temperature processes and some require high pressures.     

Carbazole/oligocarbazoles substituted silanes as wide bandgap host materials for solution-processable electrophosphorescent devices

We have designed and synthesized a series of organic wide bandgap materials, namely DCzSiCz, DDCzSi and DTCzSi, by incorporating carbazole/oligocarbazoles via a silicon-bridged linkage mode. All the materials show good thermal stability and excellent solution-processibility. Their HOMOs and LUMOs could be tuned to facilitate the efficient carriers injection by the incorporated carbazole/oligocarbazoles, while their singlet and triplet energy levels still maintain high levels, all above 3.44 eV and 2.87 eV, respectively. High efficient blue electrophosphorescent devices with low turn-on voltage are realized using DCzSiCz, DDCzSi and DTCzSi as hosts for FIrpic through solution-processable method. Among them, DCzSiCz-based device demonstrates the best performance, showing a maximum brightness of 6600 cd m⁻² at 11 V and maximum luminous efficiency of 8.40 cd A⁻¹ at 5 V.     

Study on stacking faults and microtwins in wide bandgap II-VI semiconductor heterostructures grown on GaAs

ZnMgSSe and ZnSSe layers grown on GaAs substrates with GaAs buffer layers by molecular beam epitaxy have been examined by transmission electron microscopy (TEM). The depth level at which paired triangular stacking faults are nucleated in the ZnMgSSe/GaAs heterostructure has been investigated by using the plan-view TEM technique. It has been found that in the ZnMgSSe/GaAs heterostructure the nucleation of the paired stacking faults occurs within a range of depth which starts at the II-VI/GaAs interface and ends at a level that is above the interface by about 120 nm. The dominant type of defects in ZnSSe layers, which have the single triangular shape, has been identified to be microtwins by high resolution TEM.     

Annealing effects of NTD silicon for semiconductor power devices

The use of neutron transmutation doped (NTD) Si has become very important for processing high-voltage power devices. A simple annealing process is usually required to anneal the lattice defects caused by neutron irradiation. This is usually performed by the silicon supplier by annealing the silicon crystal at a low temperature (approximately 700°C). High-voltage power devices, however, require much higher processing diffusion temperature. In situ annealing of silicon, therefore, can occur during device processing. Furthermore, we demonstrate here that higher yield can be obtained using the in situ annealing. This improvement is due to the effectiveness and uniformity of annealing of thin wafers. The uniformity and blocking voltage distribution of high-voltage rectifiers and thyristors using crystal annealed and in situ wafer annealed NTD silicon are presented.     

Fundamental power/frequency limitations of microwave semiconductor devices

The intrinsic frequency limitations on the power available from a class of microwave semiconductor devices, where charge-storage effects are present, are described.