High Performance Polysilicon Thin Film Transistor Circuits On Flexible Stainless Steel Foils

Abstract

In recent years, there has been an increased interest in the use of flexible substrates in microelectronic fabrication. Flexible substrates, such as polymers and metals have the potential to be utilized in roll-to-roll processing, resulting in low cost, rugged systems. Thin flexible stainless steel foils offer a number of advantages over polymers for device and circuit fabrication, most significantly in the increased thermal budget tolerance that they provide. This enables the utilization of high temperature processes in the fabrication and the production of high performance devices and circuits.Thin film transistors have been fabricated on thin stainless steel foils using a variety of crystallization and gate dielectric approaches. N-channel devices with average effective mobility values of 250cm2/Vs and p-channel devices with effective mobility values in the region of 90cm2/Vs were successfully fabricated. Both digital and analog circuits, such as operational amplifiers, ring oscillators and a variety of shift register designs were also fabricated, and their basic performance characteristics will be presented in this paper. The characteristics of ring oscillators having 19 inverter stages operating with speeds of 15MHz or higher, along with the characteristics of various shift register architectures with maximum operating frequencies above 1MHz, will be reported. The impact of process and design parameters on their operation was evaluated and will be addressed in this paper.The results that are presented in this paper constitute the first successful implementation of high performance circuitry having a high degree of scalability and complexity on thin metal foils, thus making the fabrication of efficient, inexpensive and versatile systems on flexible foils for a large variety of applications a realistic prospect.

Printing technology for ubiquitous electronics

“…In practice, large gate widths in low-mobility devices may increase the area. Modeling a printed silicon circuit with six layers (similar to standard thin film MOS polysilicon TFTs (Carey and Smith, 1999;Afentakis et al, 2003) with two level metal, the transistor process cost is $8.3 £ 0 2 6 , which is , 640x larger than the average total cost of ULSI transistors.…”

“…Using layer thicknesses based on polySi data (Carey and Smith, 1999;Afentakis et al, 2003) (see the Appendix for details), and costs of insulators (except gate) at $0.01/g, gate dielectric $0.05/g (150 nm), metal $0.1/g (200 nm) and semiconductor $0.3/g (150 nm), plus passivation on the substrate and on top (full area coverage), a cost of $1.7 £ 10 2 8 /transistor was obtained, far below the process cost, but slightly greater than the total cost of a ULSI transistor. Thus, even if some of the materials are substantially cheaper, the total is not dramatically lower than the silicon IC components.…”

“…Kovio reportedly uses stainless steel for process temperature compatibility (Johnson, 2007). The need for smoothness of stainless steel for electronics has been emphasized (Afentakis et al , 2003); material suitable for thin film amorphous Si solar cells is ∼$10‐12/m 2 (Cannella, 2002). This completely dominates the materials cost.…”

Fabrication processes and experimental validation of a planar PV power system with monolithically embedded power converters

“…The use of large area electronics or Macro-electronics is a relatively recent idea, although significant work has been done to integrate the display driver circuitry on the same substrate with the display itself used in large screen TV monitors. Therefore, there exist many success stories in the literature in this regard [1]. On the other hand, power electronic components such power semiconductor switches, resistors, capacitors, inductors and other passive elements have been used in the form of discrete components on printed circuit boards (PCB) for several decades.…”

Fabrication of Electrophoretic Display Driven by Membrane Switch Array

“…1) Most of these devices have been driven using backplane of thin-film transistors fabricated using conventional semiconductor technology. 2,3) Thus far, the enthusiasm has been focused on increasing display resolution. However, there is a substantial demand for developing large-scale displays for applications such as digital signage and point-of-purchase (POP) displays.…”