Fully Three-Dimensional Silicon-Integrated Dielectric Capacitor at 1 µFmm-2 for on-Chip Energy Storage

The increasing request of on-chip energy storage devices is driven by the augmented connectivity between people and things for IoT, portable, and wearable electronic applications. These systems require high performance components with low power consumption, compact size, and high energy storage capability. Supercapacitors (SCs) achieve capacitance density in the order of 0.1–1 mF/mm2. Nonetheless, their poor performance in terms of operation frequency (from Hz to tens of Hz, rarely beyond 1 kHz) and voltage (rarely exceeding 2 V), together with their low compatibility with standard integrated circuit (IC) technologies, have inhibited their integration to date. Dielectric capacitors (DCs) make use of solid-state dielectrics sandwiched between two conductive electrodes. These capacitors operate at high frequency (up to a several MHz) and voltages (exceeding tens of Volt). However, the areal capacitance of DCs is order of magnitude smaller than that of SCs. The use of high dielectric constant materials (k>10) and the exploitation of the third dimension (3D capacitor) to increase the effective surface area of the capacitor per unit volume have been proposed. In this work, we successfully address the challenge of achieving a 3D silicon-based dielectric capacitor with high capacitance density and large operation voltage and frequency range, using a fabrication process that is compatible with silicon ICs technology. Specifically, we report on 3D DCs fully integrated in a silicon chip with areal capacitance up to 1 μF/mm2 by atomic layer deposition of conductive (TiN) and high-k dielectric (Al2O3 and HfAlOX) nanocoatings (20 and 40 nm) into trenches electrochemically etched in silicon with aspect ratio up to 100 [1]. The 3D DCs operate up to 70kHz with an excellent stability with voltage (up to 16V) and temperature (up to 100°C), over 100 h of continuous operation (>108charge/discharge cycles). The 3D DCs exhibit power and energy densities of 566 W/cm2 and 1.7 μWh/cm2, respectively, greater that those of most state-of-the-art dielectric capacitors and supercapacitors. [1] L. M Strambini, A. Paghi, S. Mariani, A. Sood, J. Kalliomäki, P. Järvinen, F. Toia, M. Scurati, M. Morelli, A. Lamperti, G. Barillaro, Three-dimensional silicon-integrated capacitor with unprecedented areal capacitance for on-chip energy storage, Nano Energy, 68, 104281 (2020)