Investigations on an Ultra-Thin Bendable Monolithic Si CMOS Image Sensor

In this paper, theoretical as well as experimental results of the investigations on a bendable ultrathin Si monolithic CMOS image sensor are presented. The electro-optical behavior of a thinned flexible CMOS active pixel sensor for the application of uniaxial mechanical stress is theoretically and experimentally analyzed. The necessity of a correlated double sampling readout scheme to achieve a stress-independent operation is underlined. Optical as well as electrical characteristics of standard photodiodes on ultrathin silicon chips embedded into a polyimide foil under several bending configurations are discussed and experimental data are presented. Moreover, design rules for the stress-independent operation of a flexible ultrathin image sensor are given and the thinning and the encapsulation processes are shortly presented.

I. Introduction

Flexible electronics have gained an increasing attention during the last years with applications ranging from foldable displays up to consumer and biomedical devices. Ultra-thin silicon (Si) chips with thicknesses less than 20 are being employed toward this direction, i.e., for realizing bendable, foldable and in general flexible systems such as retinal implants, the electronic paper, 3-D ICs etc. [1].