Electrically powered implanted actuators are commonly used for neural tissue micro-stimulation to research treatment of a variety of neurological disorders. Currently, these actuators are being activated by electrical power delivered through electrodes tethered to the skull, resulting in tissue damage for long-term implants. Optically powered silicon photodiodes can electrically stimulate neural tissue without causing tissue damage. At the near-infrared range of 850nm, an optical power source can safely penetrate human tissue. We have designed and fabricated silicon photodiodes for implantation and opto-electrical stimulation of neural tissue to meet both electrical performance and tissue biocompatibility demands. Having shown successful performance characteristics in the first round of device development, a second round of optimized photodiodes with smaller dimensions and improved stimulation performance have been designed and are currently being fabricated. These devices are expected to facilitate advancements in the study of neurological disease treatment.