基于微机电系统（MEMS）和纳机电系统（NEMS）技术的开关具有体积小、漏电流低等优点，近年来得到了广泛的关注。随着低电压互补金属氧化物半导体（CMOS）电路的兴起，MEMS/NEMS开关驱动电压高的问题逐渐成为其集成到CMOS电路中的阻碍。二氧化钒（VO2）具有相变温度略高于室温（67 ℃附近）、相变带来的应变大等优点，因此具有降低MEMS开关驱动电压的潜力。本文以实现驱动电压低（< 1 V）且工作寿命高（10^6次）的MEMS开关为研究目标，对VO2 MEMS开关及其相关技术展开研究。 首先，本文通过优化脉冲激光沉积的工艺参数，制备出了高质量的VO2薄膜，为VO2 MEMS器件的研制打下基础。 传统VO2 MEMS执行器的过高且失控的曲率，阻碍了VO2 MEMS开关的实现。为解决该问题，本文提出了一种“跷跷板”曲率控制方法。这种方法依靠调节多层薄膜之间的厚度关系实现曲率控制，具有曲率设计范围广、工艺简单等优点。基于所用薄膜残余应力的测量数据，建立了高精度的VO2 MEMS执行器有限元模型。基于“跷跷板”方法和有限元仿真分析，设计并制造出曲率可控的VO2 MEMS执行器，其曲率的实验结果与设计值相符，证实“跷跷板”方法能够完全控制VO2 MEMS执行器的曲率。 基于“跷跷板”式VO2 MEMS执行器，设计了VO2 MEMS开关，并通过不同的单项实验确定了VO2 MEMS开关的各部分材料。在上述研究的基础上，首次研制出单一硅片上的完整VO2 MEMS开关。该开关的各项技术参数均符合本研究的预期指标。实验表明，VO2 MEMS开关的驱动电压为0.2 V，最高工作频率约2 kHz，工作寿命优于1×10^6次。本文研制的VO2 MEMS开关可用作环境温度感知开关或焦耳热控制开关。 最后，本文探索了VO2 MEMS开关的概念在光学领域中的应用，提出了VO2 MEMS光开关的研究目标，并设计和制造出了VO2 MEMS光开关。实验表明，这些光开关在最佳工作波长处的调制深度可达169%-277%，说明VO2 MEMS光开关具有较高的调制深度。
Switches based on micro-electro-mechanical systems (MEMS) or nano-electro-mechanical systems (NEMS) technologies have gained widespread attention in recent years due to their advantages such as small sizes and limited leakage currents. However, with the thriving of low-voltage complementary metal-oxide-semiconductor (CMOS) circuits, the high actuation voltages of MEMS/NEMS switches have gradually become the major barrier to the integration of MEMS/NEMS switches and CMOS circuits. The phase-transition material of vanadium dioxide (VO2) has many merits. For example, the phase-transition temperature of VO2 is slightly above room temperature (around 67 ℃), and the VO2 phase transition is accompanied by huge strain, etc. Therefore, VO2 has the potential to decrease the actuation voltages of MEMS switches. To realize MEMS switches with sub-1 V actuation voltages and 10^6 operating cycles, the research on VO2 MEMS switches and related technologies have been conducted and summarized in this dissertation. First, the fabrication parameters of pulsed laser deposition were optimized to deposit high-quality VO2 thin films, which laid the foundation of VO2 MEMS devices. The large and uncontrolled curvatures of conventional VO2 MEMS actuators present to be an obstacle to the realization of VO2 MEMS switches. To tackle that problem, a "seesaw" method for curvature control is introduced in this dissertation. The “seesaw” method, which controls the curvature by adjusting the thickness relationship within multi-layer structures, has advantages such as a wide range of curvature design and simple fabrication processes. A precise finite element model of VO2 MEMS actuators was established with the measurement results of the residual stresses in the involved thin films. VO2 MEMS actuators with controlled curvatures were designed and fabricated based on the “seesaw” method and the finite element model. The experimental curvatures of those VO2 MEMS actuators were in correspondence with the design, proving that the “seesaw” method is able to fully control the curvatures of VO2 MEMS actuators. A VO2 MEMS switch was designed based on the “seesaw” VO2 MEMS actuator. Materials for different parts of the VO2 MEMS switch were selected with individual tests. Based on the above research, VO2 MEMS switches in a single silicon wafer were fabricated, with performance matching the expectations. Experiments showed that, the actuation voltage, maximum working frequency, and operating cycles of the VO2 MEMS switch were 0.2 V, 2 kHz, and at least 1×10^6, respectively. Those VO2 MEMS switches can be used as environment temperature sensing switches or Joule-heating-driven switches. Finally, the concept of VO2 MEMS switches was expanded into the optical field with the introduction of VO2 MEMS optical switches. VO2 MEMS optical switches were designed and fabricated. Experimental results showed that, the modulation depths of such optical switches reached 169%-277% at the optimized working wavelengths, indicating that the VO2 MEMS optical switches have relatively high modulation depths.
