Considerations and Methodology to Determine R2R Manufacturing and Scaling of Electronic Devices on Flexible Stainless St
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Considerations and Methodology to Determine R2R Manufacturing and Scaling of Electronic Devices on Flexible Stainless Steel Foil Substrates Aditi Chandra1; Mao Takashima1; Joey Li1; Patricia Beck1; Scott Bruner1; Dylan Tinsley1; Raghav Sreenivasan1; Arvind Kamath1 1
Thinfilm Electronics, San Jose, CA, 95134 United States.
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. INTRODUCTION The demand for low cost, high volume manufacturing of electronic disposable devices integrated in smart packages necessitates the need for roll to roll (R2R) manufacturing of RF, display battery, and sensor elements. Printed electronics in conjunction with R2R and sheet-based manufacturing has received considerable attention in recent years1-4. We have previously shown that high performance polysilicon TFT devices based on printable silicon ink and screen printed dopants on a sheet-based high temperature steel substrate can be used to make low cost RF capable devices (with limited transistor count) in a production environment 5-7. A key enabling technology is the use of screen printed n and p type silicon dopants that completely eliminates expensive ion implantation equipment from the manufacturing flow. This results in a low maintenance, high throughput, and low step count process integration module. This work examines the substrate choice criteria for high temperature R2R. We also present a methodology encompassing sensitive electrical characterization and optical inspections as a method for evaluating suitability for a process to move from sheet based to R2R based.
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