Considerations and Methodology to Determine R2R Manufacturing and Scaling of Electronic Devices on Flexible Stainless Steel Foil Substrates

Abstract

Stainless steel substrates enable a combination of low cost, flexibility, durability, high processing temperatures, and sub-100 um thickness making it well suited for sheet based and roll-to-roll processing. NFC (13.56 MHz) based circuits using high performance polysilicon TFTs on steel sheets have been manufactured using a hybrid printed process in a production environment. The process scheme utilizes a hybrid, additive materials approach encompassing low cost manufacturing steps such as slot die coating and screen printing of silicon and dopant inks to enable a high throughput, low cost, manufacturing flow. This paper describes the approach for migrating from a sheet-based hybrid process flow to a R2R-based process. A comparison of substrate choices and considerations for R2R process integration is presented. A sensitive electrical method for evaluating the feasibility of R2R-based process integration schemes and materials selection is presented. MIM capacitor leakage, TFT device characteristics, NFC circuit performance, and defect density considerations are shown as a function of steel substrate bending, down to a diameter of 0.75 inches. Electrical characteristics and optical inspections show no measurable change to insulator characteristics, demonstrating a high degree of flexibility and overall device and process capability for R2R processing.

Roll‐to‐Roll Fabrication of Solution Processed Electronics

“…For R2R processing to be applicable, the used substrates obviously need to display a certain degree of mechanical flexibility. Several types of substrate materials have been reported for use in R2R manufacturing, the most important ones being thin glass, polymer films, and metal foils or metallized polymer films . For certain applications, also paper substrates have been used .…”

82‐2: Invited Paper: Roll‐to‐Roll Processing of Polysilicon TFTs on Flexible Large Area Stainless Steel Substrates

“…This results in a high throughput, low maintenance, and low step count process, capable of migrating to a R2R manufacturing line. The advantages of steel over other flexible substrates for R2R, including dimensional stability, flexibility, resistance to chemical attack, and non-permeability to water and oxygen, have been discussed elsewhere [5]. In addition, steel provides a mechanical robustness with more than 10 times greater impact resistance compared to silicon and a capability to withstand higher compressive pressures.…”