Physics of Future Ultra High Speed Transistors - Part II: New Concepts

SiGe/Si - MODFETs have obtained encouraging results with maximum oscillation frequencies for p-and n-channel devices around 100 GHz. The SiGe/Si system is the only one with nearly symmetrical transport properties of holes and electrons. Future development of silicon based ultra high frequency devices will be strongly influenced by integration demands, quality of MOS gates on heterostructures, strained layer engineering and band ordering. Devices which exploit tunnelling, coherent transport and transit time effects will gain importance. Room temperature tunnelling via SiGe quantum wells and quantum dots is proposed and partly tested. Resonance phase operation may allow oscillators with defimed frequencies above the conventional frequency limits.