Fabrication of Flexible Image Sensor Based on Lateral NIPIN Phototransistors

Summary

We present a detailed method to fabricate a deformable lateral NIPIN phototransistor array for curved image sensors. The phototransistor array with an open mesh form, which is composed of thin silicon islands and stretchable metal interconnectors, provides flexibility and stretchability. The parameter analyzer characterizes the electrical property of the fabricated phototransistor.

Abstract

Flexible photodetectors have been intensely studied for the use of curved image sensors, which are a crucial component in bio-inspired imaging systems, but several challenging points remain, such as a low absorption efficiency due to a thin active layer and low flexibility. We present an advanced method to fabricate a flexible phototransistor array with an improved electrical performance. The outstanding electrical performance is driven by a low dark current owing to deep impurity doping. Stretchable and flexible metal interconnectors simultaneously offer electrical and mechanical stabilities in a highly deformed state. The protocol explicitly describes the fabrication process of the phototransistor using a thin silicon membrane. By measuring I-V characteristics of the completed device in deformed states, we demonstrate that this approach improves the mechanical and electrical stabilities of the phototransistor array. We expect that this approach to a flexible phototransistor can be widely used for the applications of not only next-generation imaging systems/optoelectronics but also wearable devices such as tactile/pressure/temperature sensors and health monitors.

Introduction

Bio-inspired imaging systems can provide many advantages compared to the conventional imaging systems^1,2,3,4,5. Retina or hemispherical ommatidia is a substantial component of biological visual system^1,2,6. A curved image sensor, which mimics the critical element of animal eyes, can provide a compact and simple configuration of optical systems with low aberrations⁷. Diverse advancements of f....

Protocol

CAUTION: Some chemicals (i.e., hydrofluoric acid, buffered oxide etchant, isopropyl alcohol, etc.) used in this protocol can be hazardous to health. Please consult all relevant material safety data sheets before any sample preparation takes place. Utilize appropriate personal protective equipment (e.g., lab coats, safety glasses, gloves) and engineering controls (e.g., wet station, fume hood) when handling etchants and solvents.

1. Si Doping and Isolation

NOTE: See Figure 1a - 1d.

1. Prepare a doped SOI wafer by ion implan....

Results

Figure 3a and 3b show the designed and fabricated structure of NIPIN PTR considering previous studies^2,23. The inset in Figure 3a exhibits a basic I-V characteristic of PTR. The detailed structural parameters of PTR are shown in Figure 3b. The doping process for a Si layer on an SOI wafer was conducted using the ion implantat.......

Discussion

The fabrication technology described here contributes significantly to the progress of advanced electronics and wearable devices. The fundamental concepts of this approach use a thin Si membrane and metal interconnectors capable of stretching. Although Si is a brittle and hard material that can easily be fractured, a very thin Si layer can obtain a flexibility^26,27. In the case of the metal interconnector, the wavy shape offers stretchability and flexibility

Materials

List of materials used in this article

Name	Company	Catalog Number	Comments
MBJ3	karl suss	MJB3 UV400 MASK ALIGNER	Mask aligner
80 plus RIE	Oxford instruments	Plasmalab 80 Plus for RIE	ICP-RIE
80 plus PECVD	Oxford instruments	Plasmalab 80 Plus forPECVD,	PECVD
SF-100ND	Rhabdos Co., Ltd.	SF-100ND	Spin coater
Polyimide	Sigma-Aldrich	575771	Poly(pyromellitic dianhydride-co-4,4′-oxydianiline), amic acid solution
SOI (silicon on insulator) wafer, 8inch	Soitec	SOI (silicon on insulator) wafer, 8inch	8inch SOI Wafer (silicon Thickness: 1.25μm)
Acetone	Duksan Pure Chemicals Co., Ltd.	3051	Acetone
Isopropyl Alcohol (IPA)	Duksan Pure Chemicals Co., Ltd.	4614	Isopropyl Alcohol (IPA)
Buffered Oxide Etch 6:1	Avantor	1278	Buffered Oxide Etch 6:1
HSD150-03P	Misung Scientific Co., Ltd	HSD150-03P	Hot plate
AZ5214	Microchemical	AZ5214	Photoresist
MIF300	Microchemical	MIF300	Developer
SYLGARD184	Dow Corning	SYLGARD184	Polydimethylsiloxane elastomer
Hydrofluoric Acid	Duksan Pure Chemicals Co., Ltd.	2919	Hydrofluoric Acid
CR-7	KMG Chemicals, Inc	210023	Chrome mask etchant
MFCD07370792	Sigma-Aldrich	651842	Gold etchant