兰州大学机构库 >物理科学与技术学院
静电感应晶闸管(SITh )的器件模型与负阻转折机理
Alternative TitleDevice Models and Breakover Characteristics of Static Induction Thyristor (SITh)
汪再兴
Thesis Advisor李思渊 ; 杨建红
2007-11-01
Degree Grantor兰州大学
Place of Conferral兰州
Degree Name博士
Keyword静电感应晶闸管 半导体器件
Abstract

静电感应晶闸管(SITh)是一种依靠静电感应机制工作的功率半导体器件,即依靠栅偏压和阳(漏)偏压的静电感应作用控制沟道势垒高度从而实现器件的开通和关断。相对于其它种类的功率半导体器件(如 SCR、GTO、IGBT、VDMOS 等),SITh最明显的特点是具有明确的阻断态和导通态,具有通态压降低(1.0~3.5V)、开关速度快(0.5~1.5MHz)、电流密度高(~800A/cm2 )、功率处理能力强(10~15kVA)、转换效率高(>90%)等一系列优点,兼顾了速度和功率两方面的要求,更适合于作为大功率开关器件使用。这对传统的电力系统的效能提升、模式改造、以及民用节能具有重要的技术、经济意义。本论文的目的在于,通过对 SITh 的器件物理分析,建立 SITh的工作模型,明确影响阻断态和导通态特性指标的主要因素,以及开关(转变)机理和开关过程的特点,从而为 SITh 的设计、制造、性能优化、应用控制提供理论依据。

本论文研究的主要问题是 SITh 负阻转折特性的发生机理及其特点。为此,本论文以基本的 PN 结和双极晶体管(BJT)作用理论为基础,采用理论分析、数值模拟、以及实验观测相结合与对比的方法,做了以下几个方面的工作:(1)对影响 SITh 特性最为敏感的结构参数-沟道宽度,从栅区扩散工艺条件角度做了理论和实验研究(第二章)(该结构参数实际上是由形成栅区的扩散工艺条件调节和控制的);(2)对 SITh中存在的本征 SIT 结构及其特性作了专门的理论分析(第三章),以便于理解它在 SITh工作过程中的作用,阐明了沟道势垒高度随各区几何参数和掺杂浓度以及外加偏压的变化规律,并给出了势垒高度和 SIT、SITh I-V 关系的解析表达式;(3)将 SITh看作是由本征 SIT、阳极 PN 结、以及寄生 BJT 构成的一个有机整体,分别分析了它们在阻断态和导通态各自所起的作用,对阻断态和导通态分别建立了器件模型,并由此解释了负阻转折的发生机理(第四章);(4)对所建立的器件模型依据实际测试结果作了实验验证,证明了这些模型的合理性和实用性(第五章)。

通过以上几方面的工作,本论文取得了以下几方面的研究结果:(1)给出了沟道势垒高度和 SIT、SITh 端电流的解析表达式,这些表达式与以往的唯像理论不同,综合反映了材料、结构参数和外加偏压的作用,其中的待定参数通过简单的实验测量就可确定,进而指出:势垒高度与外加偏压并非以往认为的那样是简单的线性关系,而是从小电流状态到大电流状态由某种形式的指数关系转变到线性关系,器件的 I-V特性也不是简单的指数关系;根据这些表达式计算得到的结果与模拟结果吻合得很好,与实验规律也相互符合;(2)针对 SITh 的阻断态,提出并建立了 SIT-BJT 耦合作用模型,认为 SIT 的阴极电流是寄生 BJT 的基极电流,从而阐明了阻断态各端电流之间的关系,并且得到了实验验证;(3)针对 SITh 的导通态,提出并建立了类 PIN 作用模型,认为导通态的 SITh 其实质是一个由 p+ 阳极-n- 漂移区-n+ 阴极构成的一个 PIN二极管,成功地解释了导通态低压大电流的特征,该模型也得到了实验验证;(4)提出了器件由阻断态向导通态转变的原因是 Kirk 效应导致的这样一种观点,这一观点得到了数值模拟结果和实验结果的支持,因为无论是从模拟分析、理论分析、还是从实验测量几方面来看,都表明转折时寄生 BJT 的共射极电流增益 β≈ 1,阴极电流 IK ≈栅极电流 IG ,寄生 BJT 处于深度饱和状态;转折后阴极电流和栅极电流也基本相等且都很大,这也解释了为什么 SITh 器件在工作过程中容易发热烧毁的原因;(5)研究发现,对 SIT,由于负的栅偏压和正的漏偏压对势垒高度的控制作用是相反的,如果将二者作用相互抵消对应的阳极偏压记为 VDS0 、将漏极偏压为零时的势垒高度记为 φC0 、将阻断态任意偏压下的势垒高度 φ 用 φC0 归一化、V DS 用 VDS0归一化,则得到的φ/φC0 ~VDS /VDS0曲线是一条“普适曲线”,曲线形状与外加偏压(VGS 、VDS)无关;(6)研究发现,对SITh,如果将阻断态下的阳极偏压 V AK 对阻断电压归一化,将不同栅偏压下的 I-V 特性曲线进行比较,可以明显看出栅偏压和阳极偏压对器件控制作用的巨大差异,并且不同栅偏压下的各条 I-V 特性曲线在转折点附近基本交于一点,表明在各种栅偏压下的转折电流基本相等;(7)本论文还通过数值模拟手段计算得到了各种偏置条件下SITh 器件内部的电势和载流子浓度分布及其变化,特别是计算得到了导通态的 I-V特性曲线,这一结果目前尚未在其它地方见到过。

本论文所取得的结果,可以在较大程度上避免当前器件结构设计的盲目性,增强制造过程中技术措施的针对性,对材料、结构、工艺和特性之间的相互制约关系取得更加深入的认识,并为解决器件实际使用过程中的相关问题(如开态栅电流很大、开关速度偏低、短时间内发热严重甚至烧毁等)提供新的思路。

Other Abstract

As a power semiconductor device, Static Induced Thyristor (SITh) works on the mechanism of static induction which is that the conduction and blockage of the device is dominated by the channel barrier φC controlled by the mechanism of static induction of gate bias and anode/drain bias. Compared with other power semiconductor devices, such as SCR,GTO, IGBT, VDMOS and etc, the distinctive features of SITh are grouped into giving attention to balancing the two aspects of requirement-speed and power to be more suitable
for high power switching devices. Those features are as follows: explicit conducting and blocking states, low conducting-state voltage (1.0~3.5V), rapid switching speed
(0.5~1.5MHz), high current intensity (~800A/cm2 ), strong power-handling capability (10~15kVA), high conversion efficiency (>90%). It will be of great technical and economic significance for efficiency promotion and mode reconstruction of traditional power systems and energy saving in civilian use. The objective of this dissertation is to establish the device models of SITh and define the key factors impacting the characteristic indices of its conducting and blocking states by analyzing device physics in order to provide the theoretical basis for design, manufacture, performance-optimizing and application of SITh.

The major issue of the dissertation is on investigating the occurrence mechanism and properties of the negative-resistance characteristic of SITh. Based on the fundamental
theories of PN junction and BJT, the combination of approaches of theoretical analysis,numerical simulation and experiment is used to do the following research. (1) The channel width, the most sensitive structural parameter to affect SITh’s characteristic, is studied from the view of the technological condition of the gate diffusion process theoretically and experimentally (Seen in Chapter 2). (2) The intrinsic SIT structure and properties in SITh
operation process are analyzed theoretically (in Chapter 3). After illustrating the variation of φC with geometrical parameters, doping concentration, and applied bias, the analytical expressions of  φC and I-V characteristics of SITh as well as SIT are presented. (3)Considering SITh as a uniform body consisting of intrinsic SIT, anode PN junction and parasitic BJT, Chapter 4 analyzes the effects of each part respectively and establishes device models for conducting/blocking state to explain its negative resistance transition. (4) To prove the rationality and practicality of these models, experimental validation according to the actual testing results is finally given in Chapter 5.

This dissertation obtains the following achievements. (1) The analytical expressions of φC with terminal currents of SIT and SITh is derived. They are entirely different from previous phenomenological theories and comprehensively reflect the parameters of materials, structures and applied bias. It’s further argued that the relationship between φC and applied bias changes from exponentially at low-level current to linearly at high-level current. It is not simply linear as thought before, neither does the I-V characteristic. The results are in concordance with both numerical simulation and experimental ones mutually.(2) For the conducting state of SITh, the SIT-BJT coupled model validated by experiments is proposed to describe the relationship among terminal currents. (3) A model similar to PIN is provided and validated which states that SITh in conducting state is essentially a PIN diode composed of p + anode-n - drift region-n + kathode and successfully interprets the feature of high current with low voltage. (4) It’s put forward that Kirk effect causes the transition from blocking state to conducting state. It’s also supported by both numerical simulation and experimental results because base-to-collector current amplification factor β≈1 and kathode current IK≈ gate current IG shows parasitic BJT reaches deep saturated state when SITh transits. After transition, I K almost equals to IG and both of them are large. That’s why SITh often heats and burns out when operating. (5) The research illuminates that negative applied gate bias VGS and positive applied drain bias VDS have the contrary effect on controlling  φC for SIT. If we denote the counteracted anode voltage as VDS0 and the potential barrier without drain bias as  φC0 , and then normalize V DS and  φC , the curve of φ/φC0 ~VDS /V DS0 is obtained. The shape of the “universal” curve is independent of applied gate and drain bias. (6) The controlling effects of VGS and VDS are of enormous difference through comparing the I-V characteristics with various gate bias and normalized anode bias V AK . Moreover, the characteristic curves almost intersect, which indicates the transition currents with different gate bias nearly equals. (7) The distribution of potential and carrier concentration in SITh with various bias is presented as well by means of numerical simulation. Especially the I-V characteristic in conducting state is calculated which is never seen before.

URL查看原文
Language中文
Document Type学位论文
Identifierhttps://ir.lzu.edu.cn/handle/262010/229672
Collection物理科学与技术学院
Recommended Citation
GB/T 7714
汪再兴. 静电感应晶闸管(SITh )的器件模型与负阻转折机理[D]. 兰州. 兰州大学,2007.
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