MEMS静电驱动

Electrostatic actuation is favored in MEMS 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导电梳状结构组成。施加电压后，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平行移动。其关键优势在于，随着梳状结构啮合，重叠的指状结构对数量增加，但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结构位置无关的力。这种稳定、长程的驱动方式是一项革命性的突破，它使得各种器件得以应用，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。