MEMS静电驱动

Electrostatic actuation is favored in 微机电系统 due to its low power consumption (ideally zero static power), high speed, and compatibility with standard microfabrication processes. The fundamental force [latex]F[/latex] in a parallel-plate actuator is given by [latex]F = \frac{1}{2} \frac{dC}{dx}V^2[/latex], where [latex]V[/latex] is the voltage and [latex]\frac{dC}{dx}[/latex] is the gradient of the capacitance [latex]C[/latex] with respect to displacement [latex]x[/latex]. For an ideal parallel-plate capacitor, this simplifies to [latex]F approx \frac{1}{2} \frac{\epsilon A V^2}{g^2}[/latex], where [latex]\epsilon[/latex] is the dielectric permittivity, [latex]A[/latex] is the plate area, and [latex]g[/latex] is the gap. This equation highlights a critical challenge: the force is highly non-linear with displacement. As the gap closes, the electrostatic force increases rapidly, while a typical mechanical restoring force (from a spring) increases linearly. At a certain point (typically one-third of the initial gap), the electrostatic force overwhelms the restoring force, causing the movable plate to snap unstably to the fixed plate. This phenomenon, known as ‘pull-in,’ limits the stable travel range of simple electrostatic actuators.

为了克服这一局限性，人们发明了梳状驱动致动器。它由两个相互交错的梳状导电指状结构组成。施加电压时，指状结构两侧会形成静电场。这会产生一个横向力，使一个梳状结构相对于另一个梳状结构沿基板方向移动。其主要优势在于，当梳状结构…… 从事随着重叠指状电极对数量的增加，它们之间的间隙保持不变。这使得电容随位移线性变化，从而产生一个基本与可移动梳状电极位置无关的力。这种稳定、长程的驱动方式是一项革命性的突破，使其得以应用于各种器件，特别是像陀螺仪和加速度计这样需要精确稳定力反馈的高性能谐振传感器。