Two-dimensional high density piezo-FET stress sensor arrays for in-situ monitoring of wire bonding processes

This paper reports the design, fabrication, and characterization of a CMOS based two-dimensional stress sensor array. It is based on a stress sensor element exploiting the transverse pseudo-Hall effect in metal oxide semiconductor (MOS) field effect transistor (FET). In this work p-doped MOS devices (PMOS) were integrated in a 4×4 stress sensor array with a total area of only 120×120 μm². The array is connected onchip to an analog multiplexer. The new device was used for the in-situ monitoring of a ball wedge wire bonding process. It gives access to position and force information. The piezo-FET sensor array was used to spatially resolve the stress distribution underneath and close to a bondpad. A sensitivity of the array to position variations of at least 5 μm is demonstrated. Compared to previous stress sensor arrays the sensor density was increased by a factor of 22 and the number of required bondpads was reduced by a factor of 3.5.