A photosensitive readout array for optical memories

A monolithic photosensitive array has been developed for readout of digital patterns stored in holographic optical memories. To achieve large capacity, fast readout, and high optical sensitivity the photosensor array is word-organized with 256 photocells arranged in a 16 words × 16 bits-per-word configuration. The individual photocell consists of a silicon P⁺N^-N⁺photodiode as a sensor and a pair of p-channel metal-oxide-semiconductor field-effect transistors as switching elements. The photodiodes have a common cathode. Their anodes are connected to the source electrodes of the MOS devices. The gate electrodes of the MOS devices in a photocell are used as a pair of complementary address lines to select a word, whereas the drain electrodes represent digit lines. This configuration has been realized with a simple, reliable, and inexpensive process using low-temperature doped silicon oxide diffusions.