国产VDMOS器件总剂量辐射及退火效应研究

本文研究了不同辐射偏置条件下国产VDMOS器件的总剂量辐射损伤及退火效应,探讨了阈值电压、击穿电压、漏电流、导通电阻等重要的电参数随累积剂量、退火时间的变化关系。实验结果表明：阈值电压随着累积剂量的增加反而减小,在高温退火初期继续降低;在100℃退火时,在漏偏置下的击穿电压恢复并超过了辐照前的值,发生了“回弹”现象;VDMOS器件出现了LITB现象;在辐照和退火时,漏电流得到了很好的抑制,导通电阻几乎没有变化。     

Total ionizing dose effects and annealing behavior for domestic VDMOS devices

Total dose effects and annealing behavior of domestic n-channel VDMOS devices under different bias conditions were investigated. The dependences of typical electrical parameters such as threshold voltage, breakdown voltage, leakage current, and on-state resistance upon total dose were discussed. We also observed the relationships between these parameters and annealing time. The experiment results show that: the threshold voltage negatively shifts with the increasing of total dose and continues to decrease at the beginning of 100 ℃ annealing; the breakdown voltage under the drain bias voltage has passed through the pre-irradiation threshold voltage during annealing behaving with a "rebound" effect; there is a latent interface-trap buildup (LITB) phenomenon in the VDMOS devices; the leakage current is suppressed; and on-state resistance is almost kept constant during irradiation and annealing. Our experiment results are meaningful and important for further improvements in the design and processing.     

关于塑封VDMOS器件热点的研究

功率VDMOS器件作为新一代高压大电流功率器件兼有双极晶体管和普通MOS器件的优点,广泛应用于各个领域。由于功率VDMOS的工作条件恶劣,在高温大电压的应用环境下失效概率较大。在所有的失效机制中,很大一部分是由于器件无法承受瞬间高压脉冲,致使器件芯片烧坏失效。表现出的是在芯片某处产生一明显的烧穿点即所谓的"热点"。这里主要介绍了塑封VDMOS器件进行单雪崩能量测试过程和实际应用中不良品产生热点的原因,从二次击穿的角度对其进行理论解释并提出一些改进措施。     

Analysis of the quasi-saturation region of high voltage VDMOS devices

The effect of the epitaxial layer on the quasi-saturation region of the I_D(V_D) characteristic of a high voltage n-channel VDMOS structure is analysed. The proposed model takes into account the cylindrical shape of the P-well/N⁻-epilayer junction and the pinching effect of the current between neighbouring cells.     

考虑准饱和效应的一种改进VDMOS物理模型

在考虑准饱和效应的情况下,给出了能够精确描述漂移区纵向电场对电子迁移率影响的微分方程,建立了包括用解析方法求解该方程、漂移区电压降求解方法等在内的一整套处理方法,并由此提出了VDMOS的一种改进物理模型.计算结果表明,与Kim Yeong-Seuk等人提出的模型相比,该改进模型在更大的工作电压范围内都具有较高的计算精度,特别是在VDMOS发生准饱和效应时,计算精度有较大程度的提高,更加符合MEDICI的模拟结果.     

VDMOS的导通电阻模型

导通电阻是衡量VDMOS器件性能的重要参数之一,是高开关效率,低功耗VDMOS器件的主要设计指标.从VDMOS器件物理结构出发,利用半导体基本物理方程,如泊松方程,提出了一种建立精确导通电阻模型的方法.采用弧形边界对颈区电阻进行建模;通过考察载流子运动规律,求解泊松方程,结合器件结构与边界条件建立外延层模型.该方法物理概念清晰,规避了经验参数,考虑了器件结构参数对导通电阻的影响.该模型与MEDICI模拟结果相比较有良好的一致性.     

Oxide-bypassed VDMOS (OBVDMOS): an alternative to superjunctionhigh voltage MOS power devices

The superjunction concept has been proposed to overcome the ideal silicon MOSFET limit, but its fabrication was handicapped by the precise charge balance requirement and inter-diffusion problem. We report a novel device structure termed oxide-bypassed VDMOS (OBVDMOS) that requires the well-established oxide thickness control instead of the difficult doping control in translating the limit to a higher blocking voltage. This is done by using metal-thick-oxide (MTO) at the sidewalls of drift region. One can choose to have a higher blocking voltage or increase the background doping. A PiN structure, essentially identical to MOSFET during off state, was fabricated to demonstrate the proposed concept. Its measured BV_dss of 170 V is 2.5 times higher than measured conventional device BV_dss of 67 V on the same silicon wafer     

硅高压VDMOS漂移区静态物理模型的一种改进

在Yeong-seukKim等人模型[1]的基础之上,提出了一种改进的VDMOS静态物理模型。该模型特别考虑了VDMOS器件中漂移区载流子的密度分布,并且近似得到了漂移区中泊松方程的解析解。器件模拟软件MEDICI的模拟结果验证了改进静态物理模型的计算精度,与Yeong-seukKim等人的模型相比,改进模型的计算精度有较大的提高。     

VDMOS过温保护功能的实现

提出一种内部集成过温保护功能的VDMOS器件。对传统过温保护原理进行了分析,在此基础上,提出了一种适用于功率器件过温保护的改进电路结构。仿真结果表明,该器件在温度超过174℃时实现自关断,在温度降回142℃时实现自重启。该温度迟滞功能可有效防止热振荡。     

A closed form design method for the two-channel quadrature mirror filter banks

This paper presents a simple and efficient closed form method for designing two-channel linear phase quadrature mirror filter (QMF) banks with prescribed stopband attenuation and channel overlap. The proposed method is based on optimum passband edge frequency, which is calculated using empirical formulas instead of using optimization algorithm. Different window functions are used to design the prototype filter for QMF banks. When compared to other existing methods, the proposed method reduces computation time (CPU time) and amplitude distortion (e _am ), which results in a simpler and efficient design procedure for the applications where the design must be carried out in real or quasi-real-time. Several design examples are included to illustrate the proposed method and its improved performances over other exiting methods. An application of the proposed method is considered in the area of subband coding of ultrasound image.     

An equivalent circuit for charge-transfer devices

A new equivalent circuit for charge-transfer devices (CTD) is proposed. Results of circuit simulations of a string of CTD's, using the transient analysis program ASTAP, are presented. These show, among other details, incomplete transfer caused by high pulse repetition rates and backward transfer caused by excessive input charge.     

Wireless power transmission for implantable devices using inductive component of closed magnetic circuit

A mechanically flexible wireless power transmission module for implantable systems with enhanced transmission efficiency using a closed magnetic circuit (CMC) is presented. The CMC-based power transmission module consists of a primary inductor for power transmission and a secondary inductor for power reception. The CMC is fabricated by electroplating the Permalloy, composed of 81% nickel and 19% iron, on the inductors. For an open magnetic circuit (OMC), the measured power transmission efficiency was 13% when the distance between the two inductors was 5 mm. However, the efficiency was enhanced to 27% and 34% for the proposed two types of CMCs.     

Energy based closed form solution of ZCS multiresonantseries-parallel converters

Under-resonant operation of an ideal multi-resonant series-parallel power converter (MRSPC) with a capacitive output filter is modeled in this paper. This operation allows zero current switching (ZCS), which is convenient for bipolar devices. The capacitive output filtering reduces the recovery effect of the rectifier diodes and is suitable for high output voltage applications. A closed-form solution is found for this power converter, based on state space analysis using energy concepts. This approach simplifies the mathematical operations and gives better physical insight of the system variables. Based on the model, the steady-state characteristics of this power converter are derived by a simulation program, which are discussed and compared with the series resonant half-bridge power converter (SRHC). The optimum power converter parameters are found for given design requirements using computerized optimization routines. Several design examples are presented and compared with SRHC. The validity of the model is verified by SPICE simulations     

A closed form to predict outage of digital radio

A simplified formula for predicting the outage probability of an unprotected high capacity line-of-sight digital radio link operating under frequency-selective fading conditions is presented. First, the propagation anomaly is modeled as a linear in-band amplitude dispersion in conjunction with a transmission minimum (notch) frequency located within or outside the signal band of interest. A simplified expression for the outage probability of the radio system under these conditions is then obtained. This expression is based on the fade occurrence factor in the climatic region of interest, the bandwidth of the transmitted signal, the carrier frequency of operation, the modulation scheme employed and the length of the link under consideration. The formula is applied to predict the outage probability of 4 phase shift keying (PSK), 8-PSK, and 16 quadrature amplitude modulation (QAM) high capacity radio links with specified parameters. The results obtained compare favorably with measured data     

A closed form solution of Bernoullian two-classes priority queue

We investigate the effect of a two-priority policy when serving slotted traffic arriving with Bernoulli statistics. We are able to give explicit closed-form expressions for the distribution of the lengths of the high- and low-priority queue.     

具有超低导通电阻阶梯槽型氧化边VDMOS新结构

基于国际上Liang Y C提出的侧氧调制思想,提出了一种具有阶梯槽型氧化边VDMOS新结构.新结构通过阶梯侧氧调制了VDMOS高阻漂移区的电场分布,并增强了电荷补偿效应.在低于300V击穿电压条件下这种结构使VDMOS具有超低的比导通电阻.分析结果表明:较Liang Y C提出的一般槽型氧化边结构,器件击穿电压提高不小于20%的同时,比导通电阻降低40%～60%.     

具有超低导通电阻阶梯槽型氧化边VDMOS新结构

基于国际上Liang Y C提出的侧氧调制思想,提出了一种具有阶梯槽型氧化边VDMOS新结构.新结构通过阶梯侧氧调制了VDMOS高阻漂移区的电场分布,并增强了电荷补偿效应.在低于300V击穿电压条件下这种结构使VDMOS具有超低的比导通电阻.分析结果表明:较Liang Y C提出的一般槽型氧化边结构,器件击穿电压提高不小于20%的同时,比导通电阻降低40%～60%.     

An engineering model for short-channel MOS devices

An engineering model for short-channel MOS devices which includes the effect of carrier drift velocity saturation is described. Based on a piecewise carrier drift velocity model, simplified expressions for the DC drain current I_D, the small signal transconductance g_m and the output conductance g _ds in the saturation region are derived. For a given gate voltage, the expressions depend only on the threshold voltage V _T and the dimensions of the device, whose desired values are normally known     

An erase model for FAMOS EPROM devices

A physical model is presented which explains the various features of the UV erase process in FAMOS EPROM devices. An erase sensitivity factor is defined in this model, and correlated with experimental results. The erase sensitivity factor was found to be proportional to the floating-gate photoinjecting area, and inversely proportional to oxide thickness and total capacitance of the floating gate. Photoinjection of electrons from thin strips on the floating-gate edges are shown to be responsible for the charge removal from the floating gate. Quantum yields in the order of 10^-4were measured for this erase process and correlated with values found in the literature. In addition, theI-Vand spectral characteristics of photoinjected currents as low as 10^-15A from poly-Si to SiO2in FAMOS devices were measured and compared to data from Si-SiO2structures. Special features pertaining to the erase of a fully covered floating-gate FAMOS cell were investigated: the decrease in erase rate at lowDelta V_{t}is discussed, as well as the optical access to the floating gate in these devices. Based on experimental and theoretical grounds, hole injection is discounted as a possible erase mechanism in the structures investigated.