海绵城市低影响开发措施应用的风险研究

海绵城市建设是近年来城市雨洪管理方面的热点话题,经过几年的建设发展,多个试点城市已经进入考核评估阶段。回顾了透水铺装、雨水花园、绿色屋顶等3种应用广泛的低影响开发措施,归纳了此类措施长期运行情况下可能出现的雨水径流入渗、雨水资源利用、设施功能衰减等方面的风险,并提出低影响开发措施的升级改造、雨水资源利用标准的制定、管理运维方案的完善、国家政策支持与社会各界参与等风险防控对策。通过对海绵城市低影响开发措施应用的风险研究,提出未来海绵城市建设的研究重点应放在设施机理研究、寿命计算与效益评价、智慧化建设等方面。     

基于河道生态基流保障的农田生态系统服务价值损失量研究

河道生态基流保障的经济损失量直接决定着政府部门对生态基流保障的决策,同时也为河道生态基流的合理保障水平提供定量依据。基于河道生态基流保障的粮食损失引起的农田生态系统服务价值损失,提出了河道生态基流保障的农田生态系统服务价值损失量的计算方法,探讨了农田生态系统服务价值损失量的变化规律,并分析了价值损失量处理办法以及粮食市场价值对其影响变化。研究表明:来水量是计算农田生态系统服务价值损失量的基础,来水量年内分配影响农田生态系统服务价值损失量;通过水权交易和生态补偿等两种方法对河道生态基流保障的经济损失量进行处理,有利于促进农田生态系统和河道生态基流保障的协调发展;同时,粮食市场价格变化也会引起农田生态系统服务价值损失量变化。     

一种RESURF效应增强的高压低阻槽型SOI LDMOS

本文提出一种RESURF效应增强（Enhanced RESURF Effect）的高压低阻SOI LDMOS（ER-LDMOS）新结构,并研究其工作机理。ER-LDMOS的主要特征是：漂移区中具有氧化物槽;氧化物槽靠近体区一侧具有P条;氧化物槽下方的N型漂移区中具有埋P层。首先,从体区延伸到氧化物槽底部的P条,不仅起到纵向结终端扩展的作用,而且具有纵向RESURF效果,此二者都优化体内电场分布且提高漂移区掺杂浓度;其次,埋P层在漂移区中形成triple RESURF效果,能够进一步优化体内电场并降低导通电阻;第三,漂移区中的氧化物槽沿纵向折叠漂移区,减小了器件元胞尺寸,进一步降低比导通电阻;第四,P条、埋P层、氧化物槽和埋氧层对N型漂移区形成多维耗尽作用,实现增强的RESURF效应,可达到提高漂移区掺杂浓度与优化电场分布的目的,从而降低导通电阻且提高器件耐压。仿真结果表明,在相同的器件尺寸参数下,与常规槽型SOI LDMOS相比,ER-LDMOS击穿电压提高67%,比导通电阻降低91%。     

管材拉弯工艺及数值模拟分析

拉弯是管材弯曲成形的重要工艺方法,采用有限元分析软件ANSYS/LS-DYNA对不同工艺参数下的管材拉弯成形过程进行了数值模拟,通过改变相对弯曲半径R/D和相对弯曲厚度t/D,分析了拉弯工艺参数对成形过程的影响。研究结果表明:通过增大相对弯曲半径R/D或增大相对弯曲厚度t/D,降低弯曲件的等效应力,可以有效控制弯曲件壁厚的变化,有助于提高管材拉弯成形的质量。     

Experimental and theoretical study of an improved breakdown voltage SOI LDMOS with a reduced cell pitch

An improved breakdown voltage （BV） SOI power MOSFET with a reduced cell pitch is proposed and fabricated. Its breakdown characteristics are investigated numerically and experimentally. The MOSFET features dual trenches （DTMOS）, an oxide trench between the source and drain regions, and a trench gate extended to the buried oxide （BOX）. The proposed device has three merits. First, the oxide trench increases the electric field strength in the x-direction due to the lower permittivity of oxide （eox） than that of Si （esi）. Furthermore, the trench gate, the oxide trench, and the BOX cause multi-directional depletion, improving the electric field distribution and enhancing the RESURF （reduced surface field） effect. Both increase the BV. Second, the oxide trench folds the drift region along the y-direction and thus reduces the cell pitch. Third, the trench gate not only reduces the on-resistance, but also acts as a field plate to improve the BV. Additionally, the trench gate achieves the isolation between high-voltage devices and the low voltage CMOS devices in a high-voltage integrated circuit （HVIC）, effectively saving the chip area and simplifying the isolation process. An 180 V prototype DTMOS with its applied drive IC is fabricated to verify the mechanism.     

具有L型低阻导电通道的介质场增强SOI LDMOS

A low specific on-resistance（R on;sp/ SOI NBL TLDMOS（silicon-on-insulator trench LDMOS with an N buried layer） is proposed. It has three features： a thin N buried layer（NBL） on the interface of the SOI layer/buried oxide（BOX） layer, an oxide trench in the drift region, and a trench gate extended to the BOX layer.First, on the on-state, the electron accumulation layer forms beside the extended trench gate; the accumulation layer and the highly doping NBL constitute an L-shaped low-resistance conduction path, which sharply decreases the R on;sp. Second, in the y-direction, the BOX＇s electric field（E-field） strength is increased to 154 V/ m from48 V/ m of the SOI Trench Gate LDMOS（SOI TG LDMOS） owing to the high doping NBL. Third, the oxide trench increases the lateral E-field strength due to the lower permittivity of oxide than that of Si and strengthens the multiple-directional depletion effect. Fourth, the oxide trench folds the drift region along the y-direction and thus reduces the cell pitch. Therefore, the SOI NBL TLDMOS structure not only increases the breakdown voltage（BV）, but also reduces the cell pitch and R on;sp. Compared with the TG LDMOS, the NBL TLDMOS improves the BV by 105% at the same cell pitch of 6 m, and decreases the R on;sp by 80% at the same BV.