The effect of mechanical strain on the characteristics of MOS transistor structures has been measured. A strip of silicon cut from an array of MOS transistors on a slice was made into a cantilever and vibrated at about 60 Hz. The change in the device characteristics could be due to a variation in mobility or turn on voltage, but by careful investigation around the threshold of conduction it was concluded that the chief cause is due to mobility variation. This change in the mobility and hence the β of the transistor is consistent with a piezoresistive effect in the channel, the overall change in conductivity being some 50 times greater than that expected by simple geometric distortion. The piezoresistive effect in MOS structures can give rise to a change in the device characteristics due to strain built in during fabrication. This could lead to an undesirable situation in large scale arrays. Alternatively it is possible to propose using the strain sensitivity for a strain gauge and novel circuits for this purpose might be devised. © 1969.
