MEMS have proven to be effective solutions in various applications due to the sensitivity, spatial and temporal resolutions, and lower power requirements exhibited by MEMS devices. Consequently, MEMS-based sensors, such as accelerometers, gyroscopes, acoustic sensors, optical sensors, and pressure sensors, have been developed for use in a wide variety of applications.
In general, capacitive MEMS pressure sensors include a first electrode that forms one plate of a parallel plate capacitor and a second electrode that forms the other plate of the parallel plate capacitor. The first electrode is generally fixed and is typically provided in a substrate, such as a silicon wafer. The second electrode is generally movable and is incorporated into a deformable membrane that is suspended over the first electrode on the surface of the substrate. The first and second electrodes are generally spaced apart by open space, a dielectric, or another material. The deformable membrane is configured to deflect toward the substrate under an applied pressure which alters the gap between the fixed electrode and the movable electrode, resulting in a change in the capacitance between the two electrodes. By monitoring the change in capacitance between the fixed electrode and the movable electrode, a magnitude of a pressure applied to the deformable membrane can be determined.
The electrodes may be formed in a variety of different ways, such as by the deposition of a conductive film, electrical isolation of a conductive layer, and adding a spacer layer between two conductive layers. Surface micromachining is used to fabricate many MEMS devices. With surface micromachining, a MEMS device structure can be built on a silicon substrate using processes such as chemical vapor deposition. These processes allow MEMS structures to include layer thicknesses of less than a few microns with substantially larger in-plane dimensions. Frequently, these devices include parts, such as capacitive electrodes, which are configured to move with respect to other parts of the device. In this type of device, the movable structure is frequently built upon a sacrificial layer of material. After the movable structure is formed, the movable structure can be released by selective wet or dry etching of the sacrificial layers. After wet etching, the released MEMS device structure can be rinsed in deionized water to remove the etchant and etch products. For dry release, no subsequent cleaning may be necessary.
In some cases, MEMS having moving or flexing components have a limited lifespan, especially when such devices are released from the substrate and cannot benefit from added support of the substrate. In an example, MEMS devices being used on or near biological material or in a harsh environment may need to be regularly replaced to maintain accurate operation. Customary MEMS devices such as pressure sensors often require significant packaging, as well as expensive materials and processing requirements, and are thus not optimized for the uses described above. What is needed, therefore, is a flexible MEMS device that can be produced easily and at scale so as to be disposable.