Modern energy storage devices for portable and wearable technologies must fulfill a number of requirements, such as small size, flexibility, thinness, reliability, transparency, manufacturing simplicity and performance, in order to be competitive in an ever expanding market. To this end, a comprehensive inkjet printing process is developed for the scalable and low-cost fabrication of transparent and flexible micro-supercapacitors. These solid-state devices, with printed thin films of graphene flakes as interdigitated electrodes, exhibit excellent performance versus transparency (ranging from a single-electrode areal capacitance of 16 μF cm⁻² at transmittance of 90% to a capacitance of 99 μF cm⁻² at transmittance of 71%). Also, transparent and flexible devices are fabricated, showing negligible capacitance degradation during bending. The ease of manufacturing coupled with their great capacitive properties opens up new potential applications for energy storage devices ranging from portable solar cells to wearable sensors.

We present graphene-based CO₂ sensing and analyze its cross-sensitivity with humidity.

Graphene is an atomically thin material that features unique electrical and mechanical properties, which makes it an extremely promising material for future nanoelectromechanical systems (NEMS). Recently, basic NEMS accelerometer functionality has been demonstrated by utilizing piezoresistive graphene ribbons with suspended silicon proof masses. However, the proposed graphene ribbons have limitations regarding mechanical robustness, manufacturing yield, and the maximum measurement current that can be applied across the ribbons. Here, we report on suspended graphene membranes that are fully clamped at their circumference and have attached silicon proof masses. We demonstrate their utility as piezoresistive NEMS accelerometers, and they are found to be more robust, have longer life span and higher manufacturing yield, can withstand higher measurement currents, and are able to suspend larger silicon proof masses, as compared to the previous graphene ribbon devices. These findings are an important step toward bringing ultraminiaturized piezoresistive graphene NEMS closer toward deployment in emerging applications such as in wearable electronics, biomedical implants, and internet of things (IoT) devices.

In Part I, we have established a wafer-scale, CMOS compatible graphene transfer for the back end of the line integration. In Part II of this paper, we analyze statistical data of device properties and draw conclusions about possible causes of device failure. Statistical analysis is performed for device mobility and compared with the yield analysis. To complement this analysis, detailed Raman spectra are employed to analyze strain. In addition, device models developed in Part I are examined and provide further insight. From the analysis, it appears that compressive strain introduced during the graphene transfer process is may be the primary source for device failure. Moreover, we speculate based on the device statistics that the mitigation of compressive strain will improve device mobility, carrier density, and reduce variability. In addition, the presence of residues, tears, and cracks in the graphene may result in some device failure.

Graphene has extraordinary mechanical and electronic properties, making it a promising material for membrane-based nanoelectromechanical systems (NEMS). Here, chemical-vapor-deposited graphene is transferred onto target substrates to suspend it over cavities and trenches for pressure-sensor applications. The development of such devices requires suitable metrology methods, i.e., large-scale characterization techniques, to confirm and analyze successful graphene transfer with intact suspended graphene membranes. We propose fast and noninvasive Raman spectroscopy mapping to distinguish between free-standing and substrate-supported graphene, utilizing the different strain and doping levels. The technique is expanded to combine two-dimensional area scans with cross-sectional Raman spectroscopy, resulting in three-dimensional Raman tomography of membrane-based graphene NEMS. The potential of Raman tomography for in-line monitoring is further demonstrated with a methodology for automated data analysis to spatially resolve the material composition in micrometer-scale integrated devices, including free-standing and substrate-supported graphene. Raman tomography may be applied to devices composed of other two-dimensional materials as well as silicon micro- and nanoelectromechanical systems.

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.