A high-performance silicon tactile imager based on a capacitive cell

An 8 × 8-element silicon-based tactile imager fabricated using integrated-circuit process technology is described. The imager consists of an X-Y organized array of capacitive force sensors on 2-mm centers. Each transducer has a zero-pressure capacitance of 1.6 pF, an average sensitivity of 60 mV/g, and a maximum operating force of about 10 g/element. The operating force can be scaled over a wide range without changing the process or lateral array dimensions. The array is read out using a switched-capacitor charge integrator which has been shown capable of a resoiutionof about 1 fF(5 fC), giving a resolution for the imager itself (pad excluded) of more than 8 bit. The readout scheme permits off-chip electronics to be used so that the fabrication sequence requires only five noncritical masks. The array is addressed as a memory, with an access time of less than 20 µsec for 8 pixels. Scaling of the array size to other dimensions is examined and performance limitations are discussed.