Micromachines

With the development of space exploration technologies, space-grade CMOS image sensors require high-performance on-chip clock circuits with low jitter, low power consumption, small area, and excellent radiation robustness. This paper presents a radiation-hardened self-biased phase-locked loop (PLL) implemented in a 55 nm CMOS process and optimized for space-grade image sensors. By replacing the conventional dual charge pump with a current adder to separate the proportional and integral paths, and incorporating a voltage-to-current converter to eliminate the loop filter resistor, the proposed design reduces the number of nodes susceptible to single-event transient (SET) effects, lowers power consumption and area, and inherently enhances radiation tolerance. Additionally, localized radiation-hardening techniques are applied to sensitive nodes to further improve SET resilience. The proposed PLL operates over a frequency range of 0.5–2.8 GHz. At an output frequency of 1 GHz, it achieves a lock time of 2.11 μs, power consumption of 3.04 mW, phase noise of −93.84 dBc/Hz at 1 MHz offset, and RMS jitter of 7.12 ps, with a core area of 0.049 mm². Under simulated heavy-ion irradiation with a linear energy transfer (LET) of 75 MeV·cm²/mg, the hardened PLL reduces output frequency deviation by 82.86% and recovery time by 37.63% compared to an unhardened design. These results demonstrate that the proposed PLL achieves significant radiation hardness without compromising performance, power consumption, or area.

In the original publication [...]

Ferroelectric characteristics of aluminum scandium nitride (Al_1−xSc_xN) enable area-selective poling for excitation of in-plane acoustic resonance modes without the need for patterned interdigital transducer (IDT) electrodes. This work presents Lamb-wave resonators created by periodic poling of a 195-nm-thick Al_0.7Sc_0.3N film and excited using fully covered electrodes. The polarization is switched every half wavelength using sacrificial mode-mediating electrodes, and the resulting poling pattern is verified using polarization-selective wet etching. The performance is compared with uniformly poled counterparts employing IDTs to excite the same Lamb modes. At a wavelength of 4.8 µm, a periodically poled resonator operating at 1.45 GHz exhibits a quality factor (Q) of 912, approximately 15% higher than that of the IDT-based counterpart, and an electromechanical coupling coefficient (k_t²) of 5.8%, representing a 0.3% absolute reduction compared to the IDT device. The larger transduction area of the unpatterned electrodes also yields an approximately 8 dB higher admittance. Across wavelengths from 4.8 to 16 µm, the periodically poled resonators exhibit 14–50% higher Q (3–33% higher f·Q product), while IDT-based resonators show fewer spurious modes. These results indicate the potential of periodically poled Lamb-wave resonators for compact multi-frequency filter arrays, provided that their spurious modes can be suppressed.