Materials Characterization of CIGS solar cells on Top of CMOS chips
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Materials Characterization of CIGS solar cells on Top of CMOS chips J. Lu1, W. Liu2, A. Y. Kovalgin1, Y. Sun2 and J. Schmitz1 1 MESA+ Institute for Nanotechnology, University of Twente, Enschede, Netherlands, email: [email protected] 2 Tianjin Key Laboratory, Nankai University, Tianjin, PR China ABSTRACT In the current work, we present a detailed study on the material properties of the CIGS layers, fabricated on top of the CMOS chips, and compare the results with the fabrication on standard glass substrates. Almost identical elemental composition on both glass and CMOS chips (within measurement error). From X-ray diffraction measurement, except two peaks from the Si substrate, the diffraction peaks from CIGS solar cell CMOS chip and that on glass substrate coincide for all three temperatures. Helium ion microscope images of the cross-section and top view of the CIGS layers, shows that the grain size is suitable for high efficiency solar cells. INTRODUCTION Ubiquitous computing [1] requires the development of hundreds of working microelectronic devices everywhere and whenever [2]. Traditional power supplies cannot meet the energy needs of such systems: cable wiring is prohibitively expensive and sometimes unavailable; contemporary batteries can only supply very little total energy (~1-3 J/mm3) until they run out; and their lifetime is anyway limited to 1-3 years [3, 4]. The development of new batteries is slow: the energy density of batteries has only increased by a factor of five over the last two centuries [5, 6]. Advances in low-power Complementary Metal Oxide Semiconductor (CMOS) very large scale integration (VLSI) have led to the dramatic decreases in power consumption. Theoretically, it was predicated that the power consumption of different motes will be below 10 μW in the foreseeable future [7]; practically, it was reported that a CMOS image sensor can operate continuously at 70 μW/cm2 [8] and a temperature sensor requires less than 40 μW continuous power supply [9] Energy scavenging-also known as Energy harvesting-has recently drawn huge interests in both academia and industry. The concept is to power micro-electronic devices by gathering energy from the environment surrounding the device itself. It is a potential solution for powering various low power electronic devices for autonomous systems; that is, maintenance free systems. Different approaches exist for the energy harvesting, and Lu et al. [10] describe the effects of trying to monolithically integrating solar cells on top of CMOS chips as energy harvesters to convert light into electricity, thus to power the underneath integrated circuits (IC). Fig. 1 shows an envisaged system design for such PV energy harvesters.
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Fig. 1. Envisaged autonomous microchip comprising of a PV cell for energy collection, power management circuits, integrated energy storage (e.g. high-density capacitor or solid-state battery) and low-power circuits. The PV cell can be realized on the chip’s front or back side.
The Cu(In1-xGax)Se2 (CIGS) solar cell is a competitive
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