High performance polysilicon circuits on thin metal foils

In recent years, there has been a growing interest in microelectronic fabrication of thin, flexible substrates. The utilization of flexible materials in processing in motivated by the need to have low weight, high strength microelectronic circuitry compatible with roll-to-roll processing. This can lead to a new era in the fabrication of reliable, low cost and highly versatile circuits for a wide variety of applications Thin metal foils offer a number of significant advantages over polymers, their main contender in this field. The most important asset of metals for substrate application is their compatibility with high temperature processing (up to 1000degreesC), which can lead to high mobility, low drift devices. This paper examines the performance of a variety of circuits fabricated on flexible metal foils, such as stainless steel, using laser crystallized polycrystalline silicon films. The basic performance characteristics and architecture of fabricated static and dynamic shift registers and ring oscillators are discussed. N-channel thin film transistors with an average mobility of 200cm(2)/Vs were measured. Ring oscillator measurements indicate an average propagation delay of 1.38ns per inverter stage at a supply voltage of 15V. Both static and dynamic shift registers exhibit a maximum clock frequency beyond 1MHz. These circuits play a pivotal role for the fabrication of integrated display systems and most other large area electronics. This is the first time circuits of this complexity and performance have been successfully fabricated on flexible metal substrates.