MOS memory devices

Packing density is greater for metal oxide semiconductor transistors and hence it is preferred over bipolar junction transistors while designing a semiconductor chip. There are two types of metal oxide semiconductor field effect transistors- n channel MOSFET or NMOS and complementary MOSFET or CMOS. Both NMOS and CMOS devices have immense applications. NMOS is commonly used and an integral part of very large scale integration (VLSI) circuits. NMOS devices can also be used as NOR gate circuits. The memory chips developed by using NMOS devices are ROM, PROM, EPROM, EEPROM, SRAM, BSRAM and DRAM. ROM is read only memory and preferred in personal computers. PROM is programmable read only memory where ‘erase’ option is unfeasible. EPROM is erasable programmable read only memory with erasing option. EEPROM is electrically erasable programmable read only memory. SRAM is static random access memory. BSRAM is bipolar static random access memory and DRAM is dynamic random access memory.