Temperature-insensitive nanomechanical clocks in CMOS oxides

For nearly a century, quartz has been the material of choice for stable clock generation due to its temperature-insensitive stiffness, which enables mechanical oscillations with frequency instability as low as a few parts per million (ppm) across extended temperature ranges. However, the specialized processing of quartz prevents its integration within complementary metal-oxide semiconductor (CMOS) chips. The reliance on off-chip quartz clocks limits central processing units from fully utilizing emerging massively parallel computing architectures, where spatially and spectrally distributed, independent clocking is essential for achieving high speed and low power consumption. Additionally, quartz lacks inherent frequency-tuning mechanisms, limiting its ability to reduce instability levels below the part-per-billion (ppb) range, as required for precision timekeeping applications. In this work, we present an approach to match and even surpass the temperature stability of quartz in nanomechanical resonators implemented using oxides available in CMOS processes. By leveraging the composition-dependent phase transformations, we engineer the stiffness of hafnium-zirconium oxide (HZO) to complement the temperature characteristics of amorphous silicon dioxide (SiO ₂ ). This enables the creation of temperature-insensitive HZO-SiO2 nano-resonators with frequency drifts as small as 9 ppm over a 120°C range. Furthermore, by exploiting the electric-field control of HZO’s structure, we actively tune stiffness, reducing the temperature instability of HZO-SiO ₂ nano-resonators to ± 0.25 ppb. This advancement opens the possibility of replacing off-chip clocks with on-chip nanoscale alternatives that offer significantly higher stability.