Giant piezoresistance
DOI: 10.1063/1.2947637
A new experiment, conducted by scientists from France, Switzerland, and the UK, has recorded the largest-ever change brought about in a bulk material’s electrical resistance by straining the material at room temperature. Called piezoresistance, the phenomenon is often exploited in sensors. In simple metal-foil piezoresistors, the kind used to examine the integrity of a concrete wall or to monitor a prosthetic limb, the change in resistance per unit of strain (a ratio referred to as the gage factor) has a typical value of about 2. For silicon-based piezoresistors, the kind used in cell phones and airbag accelerometers, the gage factor is usually about 100. The new experiment uses a silicon–aluminum hybrid material in which the arrangement of the components, not their composition, is of paramount importance. The metal—in this case aluminum—is effectively a current shunt; applying a mechanical stress to the device deflects current toward or away from the shunt and thereby alters the device’s resistance. For appropriate geometric configurations, the researchers, led by Alistair Rowe of the École Polytechnique in Palaiseau, France, measured a gage factor of nearly 900, the largest ever seen at room temperature in a bulk material. Giant piezoresistive structures could be good news for the designers of microelectro-mechanical devices in which the measurement of ultra-small accelerations or atomic-scale deflections is important. Alternatively, higher sensitivity to movement can be translated into lower power requirements when battery energy is at a premium, as in cell phones. (
