Micro-electro-mechanical systems (or microsystems) are devices that include mechanical and electrical elements. Transducers, or devices that transform one form of energy into another form of energy, are often the electro-mechanical elements within these systems. The purpose of most MEMS is to act as sensors or actuators: that is, devices that interact directly with the physical environment. Sensors can convert such physical signals as pressure, temperature, acceleration, displacement, light, etc. into electrical signals to be processed by electronics. Moreover, electrical signals can be converted in actuators to perform work on the environment, like pumping and valve operation in microfluidics, and switching in optics and/or electronics. In many cases, physical signals induced by the package can be misinterpreted as signals from the environment. For example, in pressure sensors, packaging stress can affect the stress of the sensor (or transducer), thus affecting the output of the device. Vibrational modes in the package can influence the operation of an accelerometer. In summary, packaging affects the MEMS. This was observed very early in the development of sensors and actuators. Senturia and Smith noted in 1988,"... it is necessary to design the microsensor and the package AT THE SAME TIME.” They made two very important observations in this work: (1) “Packaging people” and “sensor people” are usually not the same people, and they do not always work well together; and (2) consideration of the package can result in elimination of possible sensor designs because they would not be feasible in a particular package.
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