Record Capacitance Density from Three-Dimensional Silicon-Based Capacitor: Toward Effective on-Chip Energy Storage

The currently growing request for a continuous connectivity between people and things has increased exponentially the demand for portable and/or wearable electronics. Thus, high performance components with more compact size, lower power consumption, and increased energy storage capability are needed. Although electronic active components have downscaled and and their performance optimized over the years, passive elements (e.g., resistors, capacitors, and inductors) have made only little progress. Supercapacitors (SCs) are electrochemical capacitors that can achieve very high capacitance density, in the order of 0.1–1 mF/mm2. Nonetheless, SC intrinsic low operation voltage (a few Volts) and reduced frequency range (up to a few hundreds of Hertz), together with their poor compatibility with integrated circuit (IC) processes have inhibited their electronic applications to date1. Dielectric capacitors (DCs) make use of solid-state dielectrics sandwiched between conductive electrodes. DCs can achieve high working frequencies, up to a several MHz, and large operating voltages, easily exceeding 5V 2. However, DC capacitance density is orders of magnitude smaller than that of SCs. Nowadays, it is still challenging to simultaneously achieve capacitors with high capacitance density, wide working frequency range, and small footprint for future electronic applications, with a fabrication process that is compatible with ICs technology. Here, we demonstrate the possibility to integrate, on a silicon chip, 3D microcapacitors with capacitance density up to 1 μF/mm2 by leveraging the atomic layer deposition of conductive (TiN) and dielectric (Al2O3and HfAlOX) nanocoatings (20 and 40 nm) into trenches electrochemically etched in silicon with high aspect-ratio (up to 100). Power and energy densities of the 3D microcapacitors, namely, 566 W/cm2and 1.7 μWh/cm2, respectively, overcome those of most state-of-the-art dielectric capacitors and supercapacitors. Further, the 3D microcapacitors feature operating frequency up to 70kHz and show excellent stability with voltage (up to 16V) and temperature (up to 100°C), over 100 h of continuous operation (>108charge/discharge cycles) . These results pave a road for effective on-chip energy storage for consumer and wearable electronic applications.