Devices Using Ultimate Silicon Technology

The size of VLSI devices is becoming smaller and smaller for higher integration and higher performance Figure 5.5.1 shows the trend for VLSI devices, taking DRAMs for example. The density of DRAMs has increased 4 times during every three years, while the gate length of MOSFETs has decreased 0.7 times during every three years. This device trend has been valid for last 25 years. If the trend continued in the future, the device size would be 0.1 μm in 10 years and 0.03 μm in 20 years. These sizes are almost comparable with the electron wavelength in semiconductors, suggesting that quantum effects or single-electron phenomena would play an important role in electron transport even in VLSI devices. Various problems and issues that limit device scaling are being discussed, including size fluctuations, statistical fluctuations of dopants in the channel, limited lithography resolution, and difficulty of manufacturing.