Spin-Coated Heterogenous Stacked Electrodes for Performance Enhancement in CMOS-Compatible On-Chip Microsupercapacitors.

Integration of microsupercapacitors (MSCs) with on-chip sensors and actuators with nanoenergy harvesters can improve the lifetime of wireless sensor nodes in an Internet-of-Things (IoT) architecture. However, to be easy to integrate with such harvester technology, MSCs should be fabricated through a complementary-metal-oxide-semiconductor (CMOS) compatible technology, ubiquitous in electrode choice with the capability of heterogeneous stacking of electrodes for modulation in properties driven by application requirements. In this article, we address both these issues through fabrication of multielectrode modular, high energy density microsupercapacitors (MSC) containing reduced graphene oxide (GO), GO-heptadecane-9-amine (GO-HD9A), rGO-octadecylamine (rGO-ODA), and rGO-heptadecane-9-amine (rGO-HD9A) that stack through a scalable, CMOS compatible, high-wafer-yield spin-coating process. Furthermore, we compare the performance of the stack with individual electrode MSCs fabricated through the same process. The individual electrodes, in the presence of 1-ethyl-3-methylimidazolium bis(trifluoromethylsulfony)imide (EMIM-TFSI), demonstrate a capacitance of 38, 30, 36, and 105 µF cm-2 at 20 mV s-1 whereas the fabricated stack of electrodes demonstrates a high capacitance of 280 µF cm-2 at 20 mV s-1 while retaining and enhancing the material-dependent capacitance, charge retention, and power density.

Enhanced Electrode Deposition for On-Chip Integrated Micro-Supercapacitors by Controlled Surface Roughening.

On-chip micro-supercapacitors (MSCs), integrated with energy harvesters, hold substantial promise for developing self-powered wireless sensor systems. However, MSCs have conventionally been manufactured through techniques incompatible with semiconductor fabrication technology, the most significant bottleneck being the electrode deposition technique. Utilization of spin-coating for electrode deposition has shown potential to deliver several complementary metal-oxide-semiconductor (CMOS)-compatible MSCs on a silicon substrate. Yet, their limited electrochemical performance and yield over the substrate have remained challenges obstructing their subsequent integration. We report a facile surface roughening technique for improving the wafer yield and the electrochemical performance of CMOS-compatible MSCs, specifically for reduced graphene oxide as an electrode material. A 4 nm iron layer is deposited and annealed on the wafer substrate to increase the roughness of the surface. In comparison to standard nonroughened MSCs, the increase in surface roughness leads to a 78% increased electrode thickness, 21% improvement in mass retention, 57% improvement in the uniformity of the spin-coated electrodes, and a high yield of 87% working devices on a 2″ silicon substrate. Furthermore, these improvements directly translate to higher capacitive performance with enhanced rate capability, energy, and power density. This technique brings us one step closer to fully integrable CMOS-compatible MSCs in self-powered systems for on-chip wireless sensor electronics.

Impact of electrode geometry and thickness on planar on-chip microsupercapacitors.

We report an assessment of the influence of both finger geometry and vertically-oriented carbon nanofiber lengths in planar micro-supercapacitors. Increasing the finger number leads to an up-scaling in areal power densities, which increases with scan rate. Growing the nanofibers longer, however, does not lead to a proportional growth in capacitance, proposedly related to limited ion penetration of the electrode.

Carbon-Based Electrode Materials for Microsupercapacitors in Self-Powering Sensor Networks: Present and Future Development.

There is an urgent need to fulfill future energy demands for micro and nanoelectronics. This work outlines a number of important design features for carbon-based microsupercapacitors, which enhance both their performance and integration potential and are critical for complimentary metal oxide semiconductor (CMOS) compatibility. Based on these design features, we present CMOS-compatible, graphene-based microsupercapacitors that can be integrated at the back end of the line of the integrated circuit fabrication. Electrode materials and their interfaces play a crucial role for the device characteristics. As such, different carbon-based materials are discussed and the importance of careful design of current collector/electrode interfaces is emphasized. Electrode adhesion is an important factor to improve device performance and uniformity. Additionally, doping of the electrodes can greatly improve the energy density of the devices. As microsupercapacitors are engineered for targeted applications, device scaling is critically important, and we present the first steps toward general scaling trends. Last, we outline a potential future integration scheme for a complete microsystem on a chip, containing sensors, logic, power generation, power management, and power storage. Such a system would be self-powering.

A Micromachined Coupled-Cantilever for Piezoelectric Energy Harvesters.

This paper presents a demonstration of the feasibility of fabricating micro-cantilever harvesters with extended stress distribution and enhanced bandwidth by exploiting an M-shaped two-degrees-of-freedom design. The measured mechanical response of the fabricated device displays the predicted dual resonance peak behavior with the fundamental peak at the intended frequency. This design has the features of high energy conversion efficiency in a miniaturized environment where the available vibrational energy varies in frequency. It makes such a design suitable for future large volume production of integrated self powered sensors nodes for the Internet-of-Things.