收缩喷嘴中的湍流Ⅰ——边界层解

应用边界层积分法,研究锥形喷嘴入口区域中湍动涡流的发展.球面坐标系中的控制方程,通过边界层的假定得到简化,并对边界层进行了积分.应用4阶Adams预测校正法求解该微分方程组.入口区域的切向和轴向速度,分别应用自由涡流和均匀速度分布来表示.由于缺乏收缩喷嘴中涡流的实验数据,需要用数值模拟对该发展模式进行逆向验证.数值模拟的结果证明,该解析模型在预测边界层参数中的能力,例如边界层的生长、剪切率和边界层厚度,以及不同锥度角时的涡流强度衰减率等.为所提出的方法引进一个简明而有效的程序,用以研究几何形状收缩设备内的边界层参数.     

A novel LDMOS with a junction field plate and a partial N-buried layer

A novel lateral double-diffused metal–oxide semiconductor (LDMOS) with a high breakdown voltage (BV) and low specific on-resistance (R_on.sp) is proposed and investigated by simulation. It features a junction field plate (JFP) over the drift region and a partial N-buried layer (PNB) in the P-substrate. The JFP not only smoothes the surface electric field (E-field), but also brings in charge compensation between the JFP and the N-drift region, which increases the doping concentration of the N-drift region. The PNB reshapes the equipotential contours, and thus reduces the E-field peak on the drain side and increases that on the source side. Moreover, the PNB extends the depletion width in the substrate by introducing an additional vertical diode, resulting in a significant improvement on the vertical BV. Compared with the conventional LDMOS with the same dimensional parameters, the novel LDMOS has an increase in BV value by 67.4%, and a reduction in R_on.sp by 45.7% simultaneously.     

Ultra-low specific on-resistance high-voltage vertical double diffusion metal–oxide–semiconductor field-effect transistor with continuous electron accumulation layer

A new ultra-low specific on-resistance(Ron,sp) vertical double diffusion metal–oxide–semiconductor field-effect transistor(VDMOS) with continuous electron accumulation(CEA) layer, denoted as CEA-VDMOS, is proposed and its new current transport mechanism is investigated. It features a trench gate directly extended to the drain, which includes two PN junctions. In on-state, the electron accumulation layers are formed along the sides of the extended gate and introduce two continuous low-resistance current paths from the source to the drain in a cell pitch. This mechanism not only dramatically reduces the Ron,sp but also makes the Ron,sp almost independent of the n-pillar doping concentration(Nn). In off-state, the depletion between the n-pillar and p-pillar within the extended trench gate increases the Nn, and further reduces the Ron,sp.Especially, the two PN junctions within the trench gate support a high gate–drain voltage in the off-state and on-state, respectively. However, the extended gate increases the gate capacitance and thus weakens the dynamic performance to some extent. Therefore, the CEA-VDMOS is more suitable for low and medium frequencies application. Simulation indicates that the CEA-VDMOS reduces the Ron,sp by 80% compared with the conventional super-junction VDMOS(CSJ-VDMOS)at the same high breakdown voltage(BV).     

高三旋轉磁場演示器的制作

高三物理补充教材中有感应电动机一节,但一般学校缺乏一个旋轉磁場演示器,对感应电动机的教学就感到枯燥乏味,教起来也有一定的困难。我們为了加強教学的直观性,制作了一只关于旋轉磁場的演示器,效果良好,能說明問題,現介紹如下: