Achieving Reliable and Ultrafast Memristors via Artificial Filaments in Silk Fibroin.

The practical implementation of memristors in neuromorphic computing and biomimetic sensing suffers from unexpected temporal and spatial variations due to the stochastic formation and rupture of conductive filaments (CFs). Here, the biocompatible silk fibroin (SF) is patterned with an on-demand nanocone array by using thermal scanning probe lithography (t-SPL) to guide and confine the growth of CFs in the silver/SF/gold (Ag/SF/Au) memristor. Benefiting from the high fabrication controllability, cycle-to-cycle (temporal) standard deviation of the set voltage for the structured memristor is significantly reduced by ≈95.5% (from 1.535 to 0.0686 V) and the device-to-device (spatial) standard deviation is also reduced to 0.0648 V. Besides, the statistical relationship between the structural nanocone design and the resultant performance is confirmed, optimizing at the small operation voltage (≈0.5 V) and current (100 nA), ultrafast switching speed (sub-100 ns), large on/off ratio (104 ), and the smallest switching slope (SS < 0.01 mV dec-1 ). Finally, the short-term plasticity and leaky integrated-and-fire behavior are emulated, and a reliable thermal nociceptor system is demonstrated for practical neuromorphic applications.

Post-Processing Trimming of Silicon Photonic Devices Using Femtosecond Laser.

Fabrication errors inevitably occur in device manufacturing owing to the limited processing accuracy of commercial silicon photonic processes. For silicon photonic devices, which are mostly processing-sensitive, their performances usually deteriorate significantly. This remains an unsolved issue for mass production, particularly for passive devices, because they cannot be adjusted once fixed in processes. This study presents a post-processing trimming method to compensate for fabrication errors by changing the cladding equivalent refractive indices of devices with femtosecond lasers. The experimental results show that the resonant wavelengths of micro-ring resonators can be regularly shifted within their free spectral range via tuning the illuminating area, focusing position, emitting power, and scanning speed of the trimming femtosecond laser with an acceptable loss increase. These experiments, as well as the trimming experiments in improving the phase balance of Mach-Zehnder interferometer switches, indicate that the femtosecond laser trimming method is an effective and fast method for silicon photonic devices.

Effective metrology and standard of the surface roughness of micro/nanoscale waveguides with confocal laser scanning microscopy.

Surface roughness is one of the important parameters affecting the optical scattering loss of dielectric waveguides. Despite extensive research interests in correlating optical losses with surface roughness, not much research focus has been dedicated to the study of an accurate metrology and measurement standard for the characterization of waveguide roughness. In this Letter, we report an effective metrology for the measurement of waveguide surface roughness, using confocal laser scanning microscopy (CLSM). We also provide the definition of surface roughness relevant to CLSM terminology based on the measured peak-to-valley (P-V) values, which can be correlated to the conventional root-mean-square roughness, by employing multi-dimensional statistical models. Finally, we demonstrate the use of CLSM metrology in measuring two-dimensional roughness of 10 µm×6 µm silica waveguides, showing an average top surface roughness of 0.151 µm and an average sidewall roughness of 0.203 µm. For comparison, the scanning electron microscopy (SEM) measurements are also carried out for the same waveguide samples, and then the measured sidewall roughness values are in the range of 0.08-0.12 µm. Since SEM measures only the amplitude of roughness profile, while CLSM measures the P-V value, after doubling the SEM value, these two methods can provide comparable results of roughness.