Energy harvesting with on-chip solar cells and integrated DC/DC converter

In this paper an energy-autonomous fully integrated photovoltaic driven harvesting solution for wireless sensor node applications is proposed. Photo diodes in parallel connection are used as on-chip micro solar cells. In order to provide the highest efficiency for ambient harvesting purposes, the n-well to p-substrate junction, which gives a negative voltage related to the p-substrate, is used. A test chip in a 130 nm CMOS technology, with different solar-cell configurations was designed and investigated. Numerous performance measurements were carried out in order to compare the on-chip solar cells. The achieved fill factor is 78% at 25 klux and 42°C. A charge pump circuit including a flying capacitor driver which allows the usage of the generated negative voltage is also presented.