Session:

Dielectric electrostatic capacitors, although they lag behind their electrochemical counterparts in energy storage, are better suited for integrated on-chip energy storage. Here we report record-high electrostatic energy storage density (ESD) and power density (PD) in back-end-of-the-line (BEOL)-compatible HfO₂-ZrO₂ (HZO)-based thin films on silicon [1]. Until now, the promise of ultrathin (anti)ferroelectricity in HZO on silicon has mostly motivated low-power computing applications [2]. However, the same features which make HZO so promising for computing – (anti)ferroelectric order down to the ultrathin regime [3,4], high permittivity via negative capacitance (NC) [2], inherently large breakdown field, conformal growth by ALD [1-4] – are also appealing for energy storage. First, to increase its intrinsic energy storage, atomic-layer-deposited antiferroelectric HZO films were engineered near its field-driven ferroelectric phase transition to exhibit amplified charge storage via the NC effect [5], which enhanced its volumetric ESD beyond the best known BEOL-compatible dielectrics (120 J/cm³). Second, to increase the overall stored energy, amorphous-templated HZO-Al₂O₃ superlattices overcame the conventional thickness limitations of HZO-based (anti)ferroelectricity to scale-up its high storage antiferroelectric NC behavior (100-nm regime). Third, to increase storage-per-footprint, the superlattices were conformally integrated into three-dimensional (3D) capacitors to boost its areal ESD (PD) to 9-times (180-times) the best-known 3D electrostatic capacitors: 80 mJ/cm² (300 kW/cm²). Notably, this ESD value exceeds that of most state-of-the-art electrochemical microsupercapacitors and is only ~ 1 order of magnitude away from commercial Li-ion microbatteries, despite boasting over 8 orders of magnitude larger PD. Therefore, this work leverages NC ferroic engineering, superlattice thickness scaling, and 3D integration to overcome the traditional capacity-speed (ESD-PD) trade-off spanning the electrostatic-to-electrochemical energy storage hierarchy. Furthermore, this work demonstrates that HfO₂-ZrO₂ can serve as the functional material system across all technologies required for energy-efficient autonomous electronics, including on-chip microsupercapacitors [1] as well as computing units [2]. Therefore, these results establish a pathway for co-designed microelectronics in which computing and energy technologies are monolithically-integrated and synergistically-operated towards enhanced energy-efficiency and sustainability.

References
[1] S Cheema, N Shanker, SL Hsu … S Salahuddin. “Giant energy storage electrostatic microsupercapacitors via negatve capacitance antiferroelectric superlattices.” In preparation.
[2] S Cheema, N Shanker … S Salahuddin. “Ultrathin ferroic HfO₂–ZrO₂ superlattice gate stack for advanced transistors.” Nature 604, 65–71 (2022).
[3] S Cheema, N Shanker, SL Hsu … S Salahuddin. “Emergent ferroelectricity in subnanometer binary oxide films on silicon.” Science 376, 648–652 (2022).
[4] S Cheema, D Kwon … S Salahuddin. “Enhanced ferroelectricity in ultrathin films grown directly on silicon.” Nature 580, 478–482 (2020).
[5] S Salahuddin & S Datta. “Use of Negative Capacitance to Provide Voltage Amplification for Low Power Nanoscale Devices. Nano Lett. 8, 405–410 (2008).

Co-Author(s): Nirmaan Shanker (University of California, Berkeley), Shang-Lin Hsu (University of California, Berkeley), Mohamed Mohamed (Massachusetts Institute of Technology), Sayeef Salahuddin (University of California, Berkeley)

Suraj Cheema

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