Electrically reprogrammable nonvolatile semiconductor memory with MNMoOS (metal-nitride-molybdenum-oxide-silicon) structure

It is clearly better to use the highly conductive molybdenum (Mo) film than polycrystalline silicon (poly-Si) film as a floating gate from the consideration of the image force effect. We propose a new mode of operation for floating gate type electrically reprogrammable nonvolatile memory. The proposed memory has the P-channel MNOS structure with the floating molybdenum gate. This floating gate is charged positively ("WRITE") by means of nonavalanche mechanism (the Schottky emission from floating gate to the Si substrate), and charged negatively ("ERASE") by the avalanche breakdown at the source and/or drain junction. The advantage of this type of memory is that it can be operated with only negative voltages. The unit cell consists of a MNMoOS and a MNOS transistor. The method of the bit selection in the cases of "WRITE" and "ERASE" operations is explained in detail, and the fully decoded 256-bit memory array is produced with 200 Å SiO2and 800 Å Si3N4gate structures. The typical value of the writing and that of the erasing voltage of this device are respectively -30 V and -20 V for 1 ms pulse duration.