A Low-Power and Low-Voltage Power Management Strategy for On-Chip Micro Solar Cells

Ismail Cevik,Suat U Ay

doi:10.1155/2015/739871

Abstract

Fundamental characteristics of on-chip micro solar cell (MSC) structures were investigated in this study. Several MSC structures using different layers in three different CMOS processes were designed and fabricated. Effects of PN junction structure and process technology on solar cell performance were measured. Parameters for low-power and low-voltage implementation of power management strategy and boost converter based circuits utilizing fractional voltage maximum power point tracking (FVMPPT) algorithm were determined. The FVMPPT algorithm works based on the fraction between the maximum power point operation voltage and the open circuit voltage of the solar cell structure. This ratio is typically between 0.72 and 0.78 for commercially available poly crystalline silicon solar cells that produce several watts of power under typical daylight illumination. Measurements showed that the fractional voltage ratio is much higher and fairly constant between 0.82 and 0.85 for on-chip mono crystalline silicon micro solar cell structures that produce micro watts of power. Mono crystalline silicon solar cell structures were observed to result in better power fill factor (PFF) that is higher than 74% indicating a higher energy harvesting efficiency.

Highlights

Sensors that can work in isolated environments for extended duration are demanded by many modern sensor applications
This study presents experimental results Journal of Sensors showing that a very simple and power efficient method can be employed to operate the on-chip photodiode micro solar cell (MSC) at the maximum power point (MPP)
The three MSC structures investigated in this study were fabricated in three different CMOS processes

Summary

Introduction

Sensors that can work in isolated environments for extended duration are demanded by many modern sensor applications. It is very hard to access these sensors to replace power sources One example of such sensor applications is implantable biomedical devices such as retinal prosthesis. Increasing power transfer efficiency in both methods requires high directivity and large coils/antennas. These are not suitable for long range applications [4]. Energy harvesters presented are arrays of on-chip micro solar cells (MSCs) composed of PN junction photodiodes that can be built using readily available layers in CMOS processes. Journal of Sensors showing that a very simple and power efficient method can be employed to operate the on-chip photodiode MSCs at the maximum power point (MPP)

Energy Harvesting with On-Chip MSCs

Low-Power Low-Voltage FVMPPT Circuit

Measurement Results

Conclusion and Discussions

Conflict of Interests