Structure-property relationships in the optimization of polysilicon thin films for electrical recording/stimulation of single neurons

Rajarshi Saha; Jitendran Muthuswamy

doi:10.1007/s10544-006-9039-x

Structure-property relationships in the optimization of polysilicon thin films for electrical recording/stimulation of single neurons

Rajarshi Saha, Jitendran Muthuswamy

Research output: Contribution to journal › Article › peer-review

8 Scopus citations

Abstract

We had earlier demonstrated the use of polysilicon microelectrodes for recording electrical activity from single neurons in vivo. Good machinability and compatibility with CMOS processing further make polysilicon an attractive interface material between biological environments on one hand and MEMS technology and digital circuits on the other hand. In this study, we focus on optimizing the polysilicon thin films for (a) electrical recording and (b) stimulation of single neurons by minimizing its electrochemical impedance spectra and maximizing its charge storage/injection capacity respectively. The structure-property relationships in ion-implanted (phosphorus) LPCVD polysilicon thin films under different annealing and doping conditions were carefully assessed during this optimization process. A 2D model of the polysilicon thin film consisting of 4 grains and 3 grain boundaries was constructed and the effect of grain size and grain boundaries on dc resistivity was simulated using device simulator ATLAS. Optimal processing conditions and doping concentrations resulted in a 10-fold decrease in electrochemical impedance from 1.1 kΩ to 0.1 kΩ at 1 kHz (area of polysilicon interface = 4.8 mm²). Subsequent characterizations showed that evolution of secondary grains within the polysilicon thin films at optimal doping and annealing conditions (10²¹/cm³ of phosphorus and annealed at 1200°C) was responsible for decreasing the impedance. Cyclic voltammetry studies demonstrated that charge storage properties of low doped (10¹⁵/cm³) thin films was 111.4 μC/cm² in phosphate buffered saline which compares well with platinum wires (∼50 μC/cm²) and the double-layered capacitance (C_dl) could be sustained between -1 to 1 V before breakdown and hydrolysis. We conclude that polysilicon can be optimized for recording and stimulating single neurons and can be a valuable interface material between neurons and CMOS or MEMS devices.

Original language	English (US)
Pages (from-to)	345-360
Number of pages	16
Journal	Biomedical Microdevices
Volume	9
Issue number	3
DOIs	https://doi.org/10.1007/s10544-006-9039-x
State	Published - Jun 2007

Keywords

Brain interface
Microelectrodes
Microfabricated neural interfaces
Micromachined biological interfaces
Neural implants
Neural interface
Neural prostheses

ASJC Scopus subject areas

Biomedical Engineering
Molecular Biology

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10.1007/s10544-006-9039-x

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title = "Structure-property relationships in the optimization of polysilicon thin films for electrical recording/stimulation of single neurons",

abstract = "We had earlier demonstrated the use of polysilicon microelectrodes for recording electrical activity from single neurons in vivo. Good machinability and compatibility with CMOS processing further make polysilicon an attractive interface material between biological environments on one hand and MEMS technology and digital circuits on the other hand. In this study, we focus on optimizing the polysilicon thin films for (a) electrical recording and (b) stimulation of single neurons by minimizing its electrochemical impedance spectra and maximizing its charge storage/injection capacity respectively. The structure-property relationships in ion-implanted (phosphorus) LPCVD polysilicon thin films under different annealing and doping conditions were carefully assessed during this optimization process. A 2D model of the polysilicon thin film consisting of 4 grains and 3 grain boundaries was constructed and the effect of grain size and grain boundaries on dc resistivity was simulated using device simulator ATLAS. Optimal processing conditions and doping concentrations resulted in a 10-fold decrease in electrochemical impedance from 1.1 kΩ to 0.1 kΩ at 1 kHz (area of polysilicon interface = 4.8 mm2). Subsequent characterizations showed that evolution of secondary grains within the polysilicon thin films at optimal doping and annealing conditions (1021/cm3 of phosphorus and annealed at 1200°C) was responsible for decreasing the impedance. Cyclic voltammetry studies demonstrated that charge storage properties of low doped (1015/cm3) thin films was 111.4 μC/cm2 in phosphate buffered saline which compares well with platinum wires (∼50 μC/cm2) and the double-layered capacitance (Cdl) could be sustained between -1 to 1 V before breakdown and hydrolysis. We conclude that polysilicon can be optimized for recording and stimulating single neurons and can be a valuable interface material between neurons and CMOS or MEMS devices.",

keywords = "Brain interface, Microelectrodes, Microfabricated neural interfaces, Micromachined biological interfaces, Neural implants, Neural interface, Neural prostheses",

author = "Rajarshi Saha and Jitendran Muthuswamy",

note = "Funding Information: Acknowledgments We would like to thank Arizona Biomedical Research Commision and the NIH for supporting this research. We gratefully acknowledge the use of facilities within the Center for Solid State Science and the Center for Solid State Electronics Research at Arizona State University.",

year = "2007",

month = jun,

doi = "10.1007/s10544-006-9039-x",

language = "English (US)",

volume = "9",

pages = "345--360",

journal = "Biomedical Microdevices",

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T1 - Structure-property relationships in the optimization of polysilicon thin films for electrical recording/stimulation of single neurons

AU - Saha, Rajarshi

AU - Muthuswamy, Jitendran

N1 - Funding Information: Acknowledgments We would like to thank Arizona Biomedical Research Commision and the NIH for supporting this research. We gratefully acknowledge the use of facilities within the Center for Solid State Science and the Center for Solid State Electronics Research at Arizona State University.

PY - 2007/6

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N2 - We had earlier demonstrated the use of polysilicon microelectrodes for recording electrical activity from single neurons in vivo. Good machinability and compatibility with CMOS processing further make polysilicon an attractive interface material between biological environments on one hand and MEMS technology and digital circuits on the other hand. In this study, we focus on optimizing the polysilicon thin films for (a) electrical recording and (b) stimulation of single neurons by minimizing its electrochemical impedance spectra and maximizing its charge storage/injection capacity respectively. The structure-property relationships in ion-implanted (phosphorus) LPCVD polysilicon thin films under different annealing and doping conditions were carefully assessed during this optimization process. A 2D model of the polysilicon thin film consisting of 4 grains and 3 grain boundaries was constructed and the effect of grain size and grain boundaries on dc resistivity was simulated using device simulator ATLAS. Optimal processing conditions and doping concentrations resulted in a 10-fold decrease in electrochemical impedance from 1.1 kΩ to 0.1 kΩ at 1 kHz (area of polysilicon interface = 4.8 mm2). Subsequent characterizations showed that evolution of secondary grains within the polysilicon thin films at optimal doping and annealing conditions (1021/cm3 of phosphorus and annealed at 1200°C) was responsible for decreasing the impedance. Cyclic voltammetry studies demonstrated that charge storage properties of low doped (1015/cm3) thin films was 111.4 μC/cm2 in phosphate buffered saline which compares well with platinum wires (∼50 μC/cm2) and the double-layered capacitance (Cdl) could be sustained between -1 to 1 V before breakdown and hydrolysis. We conclude that polysilicon can be optimized for recording and stimulating single neurons and can be a valuable interface material between neurons and CMOS or MEMS devices.

AB - We had earlier demonstrated the use of polysilicon microelectrodes for recording electrical activity from single neurons in vivo. Good machinability and compatibility with CMOS processing further make polysilicon an attractive interface material between biological environments on one hand and MEMS technology and digital circuits on the other hand. In this study, we focus on optimizing the polysilicon thin films for (a) electrical recording and (b) stimulation of single neurons by minimizing its electrochemical impedance spectra and maximizing its charge storage/injection capacity respectively. The structure-property relationships in ion-implanted (phosphorus) LPCVD polysilicon thin films under different annealing and doping conditions were carefully assessed during this optimization process. A 2D model of the polysilicon thin film consisting of 4 grains and 3 grain boundaries was constructed and the effect of grain size and grain boundaries on dc resistivity was simulated using device simulator ATLAS. Optimal processing conditions and doping concentrations resulted in a 10-fold decrease in electrochemical impedance from 1.1 kΩ to 0.1 kΩ at 1 kHz (area of polysilicon interface = 4.8 mm2). Subsequent characterizations showed that evolution of secondary grains within the polysilicon thin films at optimal doping and annealing conditions (1021/cm3 of phosphorus and annealed at 1200°C) was responsible for decreasing the impedance. Cyclic voltammetry studies demonstrated that charge storage properties of low doped (1015/cm3) thin films was 111.4 μC/cm2 in phosphate buffered saline which compares well with platinum wires (∼50 μC/cm2) and the double-layered capacitance (Cdl) could be sustained between -1 to 1 V before breakdown and hydrolysis. We conclude that polysilicon can be optimized for recording and stimulating single neurons and can be a valuable interface material between neurons and CMOS or MEMS devices.

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KW - Microelectrodes

KW - Microfabricated neural interfaces

KW - Micromachined biological interfaces

KW - Neural implants

KW - Neural interface

KW - Neural prostheses

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Structure-property relationships in the optimization of polysilicon thin films for electrical recording/stimulation of single neurons

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Keywords

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