Human-computer interfaces have been widely developed to bridge the gap in information transmission and enable the interaction between humans and computers. It provides unique opportunities to understand, augment, assist and repair the cognitive, sensory, and motor functions. Due to the soft nature of human skin and tissues, the conventional rigid human-computer interfaces face challenges in biocompatibility, wearability, comfortability, and high signal-to-noise (SNR) ratio for long-term and stable recording. Flexible devices are emerging. The flexible human-machine interface requires fundamental research in materials, mechanism, device design, and fabrication. This work focuses on developing flexible devices for human-computer interfaces which collect high-quality physical and physiological signals from animals. We have developed low impedance flexible electronic devices for high SNR recording in the motor cortex of rats: With a simple direct sputtering method, we can reduce the impedance of flexible Pt microelectrodes by 5-9-fold and reduce the thermal noise from both in vitro and in vivo recording. We also demonstrated that in addition to the surface area, the shape also affects the total impedance. We then further investigated how the design and materials of the electrodes affect the impedance, which is important for balancing the electrode sizes and recording SNR. We discovered that for materials associated with a diffusion-limited process, in small electrodes with a radius of fewer than 10 microns, the impedance transitions from area-dependent to perimeter-dependent. This indicates that when pushing for small electrodes, materials that have interactions with diffusion species in the electrolyte should be preferred. Finally, similar fabrication techniques for flexible microelectrodes can be applied to flexible photonic devices for temperature monitoring. We designed a micro-ring-resonator (MRR) based temperature sensor and demonstrated that the flexible temperature sensor doubled the temperature sensitivity compared to the conventional silicon-based MRR temperature sensor, which opens opportunities for biomedical applications in wearable devices or high sensitivity temperature monitoring. In summary, this work reports a novel method for wafer-scale low-impedance microelectrodes fabrication and provides insights into flexible device design, mechanism, and materials for high-quality recording and human-computer interfaces.