Impact of the gate driver voltage on temperature sensitive electrical parameters for condition monitoring of SiC power MOSFETs

Condition monitoring using temperature sensitive electrical parameters (TSEPs) is widely recognized as an enabler for health management of power modules. The on-state resistance/forward voltage of MOSFETs, IGBTs and diodes has already been identified as TSEPs by several researchers. However, for SiC MOSFETs, the temperature sensitivity of on-state voltage/resistance varies depending on the device and is generally not as high as in silicon devices. Recently the turn-on current switching rate has been identified as a TSEP in SiC MOSFETs, but its temperature sensitivity was shown to be significantly affected by the gate resistance. Hence, an important consideration regarding the use of TSEPs for health monitoring is how the gate driver can be used for improving the temperature sensitivity of determined electrical parameters and implementing more effective condition monitoring strategies. This paper characterizes the impact of the gate driver voltage on the temperature sensitivity of the on-state resistance and current switching rate of SiC power MOSFETs. It is shown that the temperature sensitivity of the switching rate in SiC MOSFETs increases if the devices are driven at lower gate voltages. It is also shown, that depending on the SiC MOSFET technology, reducing the gate drive voltage can increase the temperature sensitivity of the on-state resistance. Hence, using an intelligent gate driver with the capability of customizing occasional switching pulses for junction temperature sensing using TSEPs, it would be possible to implement condition monitoring more effectively for SiC power devices.     

Bidirectional triode P-N-P-N switches

The theory of operation, construction, and electrical characteristics of a new family of silicon thyristors for use as bidirectional (ac) switches are discussed. With these p-n-p-n devices, load current flow in either direction can be controlled by the application of a low voltage, low current pulse between a gate trigger terminal and one of the load current terminals. Blocking current and voltage characteristics are similar to those of a silicon-controlled rectifier (SCR); but unlike SCR's they can switch load current of either polarity. Devices have been made which, in the blocking state, will support several hundred volts with very little current flow; yet, when in the conducting state, will carry many amperes with a voltage drop of approximately a volt. Static power switching with these devices in such applications as lamp dimming, temperature controls, small motor speed controls, etc., appears to be particularly important. For triggering, these new devices depend on the manipulation of lateral current paths. The potential differences created by the flow of current in these paths determine, in turn, the lateral distribution of injected charge carriers within the device during the triggering interval. This paper presents an analysis of lateral biasing effects and the parameters which control them.     

Potential of low-voltage organic transistors with high on-state drain current for temperature sensor development

Organic transistors with high on-state drain current at gate and drain voltages of −2 V fabricated on polyethylene naphthalate foils were investigated for sensor development. Two aspects were studied: (a) the ability of such transistors to raise the sensitivity of a temperature sensor and (b) the bias stress stability of the transistors subjected to square voltage pulses that turned them on and off repeatedly. To demonstrate the first aspect, the voltage-amplifying ability of the organic transistor was used to increase the response to the temperature, ordinarily achieved with a thermistor. To achieve voltage amplification, the transistor must have on-state drain current of at least 20 μA at gate and drain voltages of −2 V. Two transistors with on-state drain current of ~60 and ~120 μA were tested, leading to voltage gain of −2.8 and −4.9 V/V, respectively, thus increasing the sensitivity of the temperature sensor by a factor of up to 5. To study the second aspect, the same square voltage pulses were concurrently applied to the gate and drain electrodes, causing the transistor to turn on and off repeatedly. The turn-on and turn-off voltages were −2 and 0 V respectively and four different pulse periods were used: T of 5, 20, 40 and 60 s. For each T, 1000 pulses with turn-on time of 1 s and varying turn-off times were applied to the transistors, leading to the aggregate net stress time of 1000 s in all cases. The changes in the on-state drain current, threshold voltage, and field-effect mobility depended on T, in spite of the net stress time being the same. The reduction in the on-state drain current did not exceed 17%, stabilization was also observed after about 500 cycles in some cases, and the maximum drop occurred for medium T, thus making T = 60 s a favorable condition for sensor operation.     

A high-current and high-temperature 6H-SiC thyristor

A 6H-SiC thyristor has been fabricated and characterized. A forward breakover voltage close to 100 V and a pulse switched current density of 5200 A/cm² have been demonstrated. The thyristor is shown to operate under pulse gate triggering for turn-on and turn-off, with a rise time of 43 ns and a fall time of less than 100 ns. The forward breakover voltage is found to decrease by only 4% when the operating temperature is increased from room temperature to 300°C. It is found that anode ohmic contact resistance dominates the device forward drop at high current densities     

Effect of Channel Width Shortening on the Stability of a-Si:H/nc-Si:H Bilayer Thin-Film Transistors

The static bias-stress-induced degradation of hydrogenated amorphous/nanocrystalline silicon bilayer bottom-gate thin-film transistors is investigated by monitoring the turn-on voltage (V _on) and on-state current (I _on) in the linear region of operation. Devices of constant channel length 10 mum and channel width varying from 3 to 400 mum are compared. The experimental results demonstrate that the device degradation is channel-width dependent. In wide channel devices, substantial degradation of V _on is observed, attributed to electron injection into the gate dielectric, followed by I _on reduction due to carrier scattering by the stress-induced gate insulator trapped charge. With shrinking the channel width down to 3 mum, the device stability is substantially improved due to the possible reduction of the electron thermal velocity during stress or due to the gate insulator quality uniformity over small dimensions.     

Gate Grounded NMOS器件的ESD性能分析

文章基于0.18μm CMOS工艺制程的1.8V NMOS器件,从工艺的角度并用TLP测试系统对栅极接地的NMOS(GGNMOS)ESD器件进行比较分析.介绍了SAB和ESD注入对GGNMOS的性能影响,影响GGNMOS ESD性能的瓶颈是均匀开启性.在GGNMOS版图等其他特征参数最优的前提下,采用SAB能改善其均匀...     

Three-terminal GaAs switches

A new three-terminal GaAs device has been developed and its switching characteristics investigated. The third ohmic contact of the device is located on a side surface near the cathode of a conventional two-terminal long n-type GaAs oscillator. High-speed switching of oscillation, with turn-on and turnoff times of one nanosecond, has been successfully obtained by applying single short triggering pulses or combined positive and negative pulses between the third contact and the cathode, using a fixed bias voltage between the cathode and the anode. The triggered oscillation can be sustained after the triggering pulse is removed if the bias voltage is above the minimum sustaining voltage of oscillation, which is about 80 to 90 percent of the threshold value. This paper will briefly review the triggering conditions of the two-terminal oscillator devices and present various current waveforms of triggered oscillations obtained with the three-terminal devices. Some correlations between the sustaining voltage of oscillation and the triggering voltage will be discussed. This device could be used as high-speed switching and memory elements in logic circuits.     

Novel passive lossless turn-on snubber for voltage source inverters

A novel passive lossless turn-on snubber with a soft-clamped turn-off snubber circuit for voltage source inverters is proposed. The energy trapped in the snubber is recovered into the DC supply and load without any active devices, associated control circuitry, or resistors. The overshoot voltage on the switches is clamped, and the peak switch current is low, making this snubber suitable for use in high-power insulated gate bipolar transistor (IGBT) inverters     

Decrease in on-state gate current of AlGaN/GaN HEMTs by recombination-enhanced defect reaction of generated hot carriers investigated by TCAD simulation

Changes in the on-state gate current of AlGaN/GaN high-electron-mobility transistors (HEMTs) under various electrical and thermal stress conditions have been analyzed by technology computer-aided design (TCAD) simulation. A larger gate current is observed under on-state bias condition than that under off-state bias condition. The TCAD simulation indicates that on-state gate current flows from the heated gate electrode to the AlGaN layer by tunneling or hopping through the gate depletion layer when we apply some deep-donor-type traps under the gate in the AlGaN barrier layer. The gate current is caused by electrons that flow and is pulled away by the applied gate-to-drain voltage under a high channel temperature condition. The deep traps benefit both the on- and off-state gate current behavior. We found that the on-state gate current is effectively decreased by electrical stress under the on-state condition. Electroluminescence measurement indicates that a large number of hot carriers are generated under this condition. The results suggest that the process-induced crystal defects are annealed out by non-radiative recombination of the generated hot carriers by a recombination-enhanced defect reaction mechanism. The change in the on-state gate current in the TCAD simulation can be successfully explained by the decrease in the donor traps.     

Switching characteristics of 45-A double-interdigitated GTO thyristors

This work presents the turn-off, turn-on and high-frequency switching characteristics of 45-A 1500-V double-interdigitated GTO switches. The devices possess the highest value of the peak interruptable anode current ever reported in the open literature for 4 × 4 mm area thyristors packed into TO-220 cases. The dynamic evaluation of devices was performed under resistive-inductive load conditions, i.e., close to those encountered in practical circuits employing GTO thyristors. The performed investigations have shown that the novel type of GTOs exhibit the best overall switching characteristics ever presented for this class of GTO switches (identical area and case). The devices performed well under high current and voltage conditions. Even the worst recorded data at higher turn-on and turn-off gains show that the developed GTOs behave as fast commutation devices consuming low input (gate) energy. It was demonstrated that fast turn-off is by no means incompatible with excellent turn-on sensitivity. A remarkable feature of devices consists in a built-in self-protection capability against electrothermal failure during gated turn-off. This unique feature enables the GTOs both to switch large amounts of load current and to safely operate at high commutation frequencies (hundred of kHz) under heavy load conditions.     

A new gate current extraction technique for measurement of on-statebreakdown voltage in HEMTs

We present a new simple three-terminal technique for measuring the on-state breakdown voltage in HEMTs. The gate current extraction technique involves grounding the source, and extracting a constant current from the gate. The drain current is then ramped from the off-state to the on-state, and the locus of drain voltage is measured. This locus of drain current versus drain voltage provides a simple, unambiguous definition of the on-state breakdown voltage which is consistent with the accepted definition of off-state breakdown. The technique is relatively safe and repeatable so that temperature dependent measurements of on-state breakdown can be carried out. This helps illuminate the physics of both off-state and on-state breakdown     

Efficiency of gate control in double-interdigitated (TIL) GTO thyristors

The research reported in this work was focused on the efficiency of gate control during turn-off in the recently developed double-interdigitated (TIL) GTO thyristors. The 8 mm² area, TO-220 packaged, high voltage test devices were investigated under both current and voltage input conditions. The main monitored parameters were: the peak turn-off gain K_off(max), the components of the turn-off time and the gate pulse width t_gr. During the tests the TIL GTOs were driven up to an anode current i_T = 50 A, a value equal to the non-repetitive peak on-state current (I_TSM) of these thyristors.The performed investigations have shown that these novel GTO devices possess a good efficiency of gate control expressed by: 1) low power consumption by the gate under both current and voltage drive conditions; 2) extremely high turn-off gain K_off(max), which is an increasing function of the anode current in a wide range of gate signals amplitudes and durations; 3) fast turn-off of large amounts of anode current with relatively short gate pulse widths; 4) substantial reduction of the storage time t_s and fall time t_f through adequate current or voltage drive. Design/behavioral details are given, which are useful in the implementation of the TIL concept in GTOs and other power switching devices, such as the bipolar transistors.     

Comments on `a nonideal macromodel of thyristor for transientanalysis in power electronic systems'

In the above-titled paper by F.J. Gracia et al. (see ibid., vol.37, no.6, p.514-20, 1990) the authors proposed a nonideal macromodel for analog power circuit simulation using SPICE. The model is quite simple and incorporates important second-order effects such as breakover voltage triggering, critical dv/dt, turn-on and turn-off times, threshold gate trigger voltage, and the nonlinear on-state characteristic. The commenter introduces some necessary corrections to the model and proposes some improvements concerning other versions of SPICE and the thermal effects on the breakdown voltage and breakover voltage turn-off characteristics     

Design aspects of MOS-controlled thyristor elements: technology,simulation, and experimental results

2.5-kV thyristor devices have been fabricated with integrated MOS controlled n⁺-emitter shorts and a bipolar turn-on gate using a p-channel DMOS technology. Square-cell geometries with pitch variations ranging from 15 to 30 μm were implemented in one- and two-dimensional arrays with up to 20000 units. The impact of the cell pitch on the turn-off performance and the on-state voltage was studied for arrays with constant cathode area as well as for single-cell structures. By realizing MOS components with submicrometer channel lengths, scaled single cells are shown to turn off with current densities of several kiloamperes per square centimeter at a gate bias of 5 V. In the case of multi-cell ensembles, turn-off performance is limited due to inhomogeneous current distribution. Critical process parameters as well as the device behavior were optimized through multidimensional numerical simulation     

Experimental investigation of turn-on spread in a thyristor

The dependence of the spreading velocity of the turned-on state in a thyristor on the load current density is measured in the presence of a turn-off gate current as well as without it. For the same thyristor the critical charge density n_c and the dependence of turn-on time constant τ₁ of turned-off parts of the thyristor on the load current density j_a flowing through the turned-on part are also measured. The data obtained make it possible to compare in detail the experimental results with the recently proposed phenomenological theory of the spreading of the turned-on state. Our investigations show that the theory describes well all the experimental results. The τ₁(j_a) dependence is of great importance in the spreading of the turned-on state. The inhomogeneities of the critical charge density n_c at different points of the structure have a considerable influence on the condition of the spread.The data obtained improve the understanding of the turn-on process and allow to calculate the spreading velocity of the turned-on state in thyristors.     

The asymmetrical field-controlled thyristor

A new device structure has been developed for field-controlled thyristors. In this structure, the uniformly doped n base of the conventional device has been replaced with a very lightly doped region near the gate and a more heavily doped region at the anode. This change in the base doping profile results in a significant improvement in the tradeoff between the forward-blocking voltage capability and the on-state forward-voltage drop. In addition, the high-resistivity region around the gate area allows the device to pinch off anode current flow at zero gate bias due to the built-in potential of the gate junction. The devices can, however, be triggered to the on-state by applying a small forward gate voltage and exhibit a forward voltage drop in the on-state which is much lower than that of conventional devices. The high resistivity of the channel area between gates also results in these devices having dc blocking gains in excess of 60, which is the highest value achieved in devices of this type. Further, because these devices have been fabricated using conventional planar processing techniques, this structure is suitable for high-volume production with high processing yields.     

The field-assisted turn-off thyristor: a regenerative device withvoltage-controlled turn-off

A solid-state switching element, the field-assisted turn-off (FATO) thyristor, has been developed. This is a regenerative device, which implies that it is capable of carrying very large current densities, with a very small forward voltage drop when it is in its on-state. Most regenerative devices cannot be turned off with a control signal; however, the structure of the FATO thyristor allows it to be switched off by applying a voltage to a high impedance, insulated-gate terminal. This device can also be fabricated with an insulated-gate turn-on structure, so that it is fully switchable using only low-current control signals. The design, fabrication, and characterization of the FATO thyristor are described     

一种200V/100A VDMOS器件开发

分析了功率MOSFET最大额定电流与导通电阻的关系,讨论了平面型中压大电流VDMOS器件设计中导通电阻、面积和开关损耗的折衷考虑,提出了圆弧形沟道布局以增大沟道宽度,以及栅氧下部分非沟道区域采用局域氧化技术以减小栅电容的方法,并据此设计了一种元胞结构。详细论述了器件制造过程中的关键工艺环节,包括栅氧化、光刻套准、多晶硅刻蚀、P阱推进等。流水所得VDMOS实测结果表明,该器件反向击穿特性良好,栅氧耐压达到本征击穿,阈值电压2.8V,导通电阻仅25mΩ,器件综合性能良好。     

Breakdown voltage and reverse recovery characteristics offree-standing GaN Schottky rectifiers

Schottky rectifiers with implanted p⁺ guard ring edge termination fabricated on free-standing GaN substrates show reverse breakdown voltages up to 160 V in vertical geometry devices. The specific on-state resistance was in the range 1.7-3.0 Ω·cm ², while the turn-on voltage was ~1.8 V. The switching performance was analyzed using the reverse recovery current transient waveform, producing an approximate high-injection, level hole lifetime of ~15 ns. The bulk GaN rectifiers show significant improvement in forward current density and on-state resistance over previous heteroepitaxial devices     

基于功率MOSFET的慢升快降型高压脉冲信号源

利用MOSFET（金属氧化物半导体场效应晶体管）导通过程中某一时段输出电流和门电压成比例的特点来获得前沿缓慢而后沿陡降的高压脉冲信号,通过栅极电阻降低脉冲前沿的上升速度;通过低驱动内阻对栅极电容电荷的快速泄放提高脉冲后沿的下降速度。在50Ω负载下脉冲的最大幅度为800V,下降沿约为15ns。