In order to balance the compressive stress of a silicon dioxide film and compose a steady MEMS structure,asilicon-rich silicon nitride film with tensil estressis deposited by plasma enhanced chemical vapor deposition process. Accurately measuring the thermal conductivity of the film is highly desirable in order to design, simulate and optimize MEMS devices. In this paper, a SiO2/SixNy bimaterial microbridge structure is presented to measure the thermal conductivity of the silicon-rich silicon nitride film by single steady-state measurement. The thermal conductivity is extracted as 3.25 W/(m K). Low thermal conductivity indicates that the silicon-rich silicon nitride film can still be utilized as thermally insulating material in thermal sensors although its thermal conductivity is slightly larger than the values reported in literature.
针对基于无线传感器网络构建的测控系统,为减少无线传感器网络固有的时变传输延时、丢包等现象对系统性能的影响,从提高系统整体性能的角度,提出一种基于网络服务质量QoS(Quality of Service)管理的多目标优化控制策略;该优化控制策略以截止期错失率作为网络QoS评价指标,针对传感器节点和汇聚节点之间的数据传输,利用PID控制器计算所有传感器节点的网络带宽需求,在此基础上,通过求解包含多个目标的最优化问题,实现各传感器节点数据包发送周期的动态调整,使得网络带宽分配适应网络QoS的变化,保证网络QoS维持在一定水平,同时满足系统其它性能指标;初步实验表明了该优化控制策略的合理性、有效性和实用性,可以广泛应用于温室、农田、苗圃等区域。
This paper presents the design principles and fabrication techniques for simultaneously forming non-coplanar resonant beams and crab-leg supporting beams of dual-axis bulk micromachined resonant accelerometers by masked-maskless combined anisotropic etching.Four resonant beams are located at the surface of a silicon substrate,whereas the gravity centre of a proof mass lies within the neutral plane of four crab-leg supporting beams on the same substrate.Compared with early reported mechanical structures,the simple structure not only eliminates the bending moments caused by in-plane acceleration,and thereby avoiding the rotation of the proof mass,but also providing sufficiently small rigidity to X and Y axes accelerations,potentially leading to a large sensitivity for measuring the in-plane acceleration.
Jian-qiang HANRi-sheng FENGYan LISen-lin LIQing LI
