Acta Physico-Chimica Sinica

Special Issue: Neural Interfaces

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Light-Induced Noise Reduction of Lightly Doped Silicon-based Neural Electrode

Chunrong Wei1,2,4, Fei Wang1,2,4, Weihua Pei1,2,4, Zhiduo Liu1,2,4, Xurui Mao1, Hongze Zhao1,2,4, Sikai Wang1,2,4, Yijun Wang1,2,4, Xiaowei Yang1,2,4, Yuanyuan Liu3,4, Shanshan Zhao5, Qiang Gui1,2,4, Hongda Chen1,2   

  1. 1 The State Key Laboratory on Integrated Optoelectronics, Institute of Semiconductors, Chinese Academy of Sciences, Beijing 100083, P. R. China;
    2 CAS Center for Excellence in Brain Science and Intelligence Technology, Beijing 100083, P. R. China;
    3 Engineering Research Center for Semiconductor Integrated Technology, Beijing 100083, P. R. China;
    4 University of Chinese Academy of Sciences, Beijing 100049, P. R. China;
    5 School of Information Technology and Engineering, Tianjin University of Technology and Education, Tianjin 300222, P. R. China
  • Received:2020-05-12 Revised:2020-06-10 Accepted:2020-06-12 Published:2020-06-15
  • Supported by:
    The project was supported by the National Key Technologies Research and Development Program of China (2017YFA0205903, 2017YFA0701100, 2016YFB0402405); the National Natural Science Foundation of China (61634006, 61671424); the Strategic Priority Research Program of Chinese Academy of Sciences Pilot Project (XDB32030100, XDB32040200); the Key Research Programs of Frontier Sciences, CAS (QYZDY-SSW-JSC004).

Abstract: Silicon-based neural probes are practical tools for recording neural cell firing. A single silicon-based needle with a width of only 70 μm, prepared using the standard complementary metal-oxide-semiconductor (CMOS) process technology, can contain thousands of electrode-recording sites. Optogenetics has made control over neuronal activity more precise. By recording the electrical activity of neurons stimulated by light, more information about brain activity can be recorded and analyzed. When yellow light or blue light is used to stimulate neurons, the photon energy is greater than the forbidden bandwidth of the silicon substrate, and the valence-band electrons are excited to the conduction band, generating electron-hole pairs. The photoinduced carrier in the silicon substrate severely disrupts the probe's signal-to-noise ratio. Decreasing the disturbance caused by light is a pragmatic way to execute recording and stimulating simultaneously. The traditional noise reduction method involves using heavily doped silicon as the substrate, reducing the carrier life by increasing the impurity concentration, and then reducing the noise of the silicon electrode under illumination. However, the heavily doped silicon substrate has more lattice defects than its lightly doped counterparts, which makes the silicon electrode fragile, and this method is not compatible with the standard CMOS process technology. On analyzing the photoinduced noise mechanism of manufacturing electrodes on lightly doped silicon substrates, we found that the inhomogeneous distribution of carriers generated by light excitation polarizes lightly doped silicon substrates. The potential caused by photoinduced polarization will affect the electrodes fabricated on it. Metalizing and grounding the lightly doped silicon substrate will effectively decrease the polarization potential. On using this method, the noise amplitude caused by the illumination can drop to 0.87% of the original value. To ensure an appropriate firing rate of neurons, the photo-stimulation frequency was chosen to be 20 Hz. Under the illumination of 1 mW·mm-2, the background noise of the electrode could be controlled below 45 μV, which meets the needs for general optogenetics applications. Modification of the lightly doped silicon substrate will meet the requirements of the neural electrode for optogenetics applications. Unlike the traditional method of reducing light-induced noise by heavily doping the entire substrate, the noise reduction method of lightly doped silicon substrate is compatible with the standard CMOS process technology. It provides a noise cancellation method for the preparation of silicon-based neural microelectrodes with dense recording sites and high channel count using standard CMOS processes.

Key words: Light-induced noise, Photoinduced carrier, Optogenetics, Lightly doped, Silicon-based neural probe


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