quality:corruption, structural:summarization
Stimulation microelectrode technologies

Microelectrodes are one of the key components of the neurostimulation, which deliver the current to neurons. Typical microelectrodes have three main components: a substrate (the carrier), a conductive metal layer, and an insulation material. In cochlear implants, microelectrodes are formed from platinum-iridium alloy. State-of-the-art electrodes include deeper insertion to better match the tonotopic place of stimulation to the frequency band assigned to each electrode channel, improving efficiency of stimulation, and reducing insertion related trauma. These cochlear implant electrodes are either straight or spiral such as Med-El Combi 40+ and Advanced Bionics Helix microelectrodes respectively. In visual implants, there are two types of electrode arrays called planar type or three dimensional needle or pillar type, where needle type array such as Utah array is mostly used for cortical and optic nerve stimulations and rarely used in retinal implants due to the possible damage of retina. However, a pillar-shaped gold electrode array on thin-film polyimide has been used in an extraocular implant. On the other hand, planar stretchable microelectrode arrays are formed from flexible polymers, such as silicone, polyimide, and Parylene as candidates for retinal implants. Regarding to DBS microelectrodes an array, which can be controlled independently, distributed throughout the target nucleus would permit precise control of the spatial distribution of the stimulation, and thus, allow better personalized DBS. There are several requirements for DBS microelectrodes that include long lifetime without injury to the tissue or degradation of the electrodes, customized for different brain sites, long-term biocompatibility of the material, mechanically durable in order to reach the target without being damaged during handling by the implant surgeon, and finally uniformity of performance across the microelectrodes in a particular array. Tungsten microwire, iridium microwires, and sputtered or electrodeposited Platinum-iridium alloy microelectrodes are the examples of microelectrode used in DBS. Silicon carbide is a potential interesting material for realizing biocompatible semiconductor devices.