Future Transistors

Scanning electron micrograph of cross-sectioned NMOS transistor.

The number of transistors on an advanced chip is now approaching 1 billion—but such density comes at an ever-increasing price in manufacturing difficulty. As transistors shrink in size, new materials and techniques must be found to ensure that they work reliably. A particular problem lies in developing new insulators for transistor gates, which control the flow of electric current through the transistor. For decades, silicon dioxide (SiO₂) was the industry's workhorse for gate insulators; but as transistors have shrunk in size, SiO₂ layers have become increasingly thinner, so that electric current can now leak through, making the transistor nonfunctional.

One solution is to use other materials, particularly metal compounds of hafnium, zirconium and aluminum, for insulating layers, or "gate stacks." Due to their high dielectric constants, or k-values, gates of "high-k" materials can be made much thicker than those of SiO₂, while achieving the same gate capacitance (with capacitance proportional to the stored electrical charge that turns a gate on and off). The AMRC is working with SEMATECH to pursue this high-k option, identifying materials and processes in time to meet industry manufacturing needs.

Other future-transistor issues being addressed by the AMRC include:

Novel transistors using new fabrication approaches, such as strained silicon, silicon-on-insulator (SOI), and nanotechnology
Investigation of new gate stack materials through computer modeling
Advanced organic/silicon devices for chemical sensing and biosensing

Semiconductors

Future Transistors