ZG
Z. Guan
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Neural microelectrode arrays (MEAs) are moving from rigid silicon toward soft and transparent substrates, so that electrical recording and optical imaging of the same cells become possible. PDMS is attractive as a substrate because it is soft, biocompatible and transparent, and PEDOT:PSS is attractive as an electrode material because its volumetric capacitance gives a low interface impedance. However, combining the two is difficult in every aspect that matters for microfabrication: surface chemistry, thermomechanical behavior, and compatibility with standard cleanroom steps. Therefore, the process has to be developed rather than adapted from an existing flow. This thesis develops a complete microfabrication process for a transparent PDMS-based MEA with PEDOT:PSS electrodes.
Firstly, we characterized the properties of the individual layers and the PEDOT:PSS/PDMS, metal/PDMS interfaces. Secondly, a full process flow was then built. The main obstacles were micromasking during the PDMS etch, film continuity across the electrode opening, and delamination of the PEDOT:PSS during development, and a solution is presented for each situation. Arrays with 30 µm and 50 µm electrodes were fabricated and prepared for subsequent bonding to a flexible PCB and encapsulation.
At the release step the stack separated at the PDMS/PDMS interface instead of at the base PDMS/SiO2 interface, so the recording face stayed sealed and the electrodes could not be measured individually. However, impedance spectroscopy performed from the front of the wafer shows that the PEDOT:PSS retains its capacitive behavior and remains functional after the full process. Once the release step is corrected in the future, the rest of the characterization of the device will be performed. ...
Firstly, we characterized the properties of the individual layers and the PEDOT:PSS/PDMS, metal/PDMS interfaces. Secondly, a full process flow was then built. The main obstacles were micromasking during the PDMS etch, film continuity across the electrode opening, and delamination of the PEDOT:PSS during development, and a solution is presented for each situation. Arrays with 30 µm and 50 µm electrodes were fabricated and prepared for subsequent bonding to a flexible PCB and encapsulation.
At the release step the stack separated at the PDMS/PDMS interface instead of at the base PDMS/SiO2 interface, so the recording face stayed sealed and the electrodes could not be measured individually. However, impedance spectroscopy performed from the front of the wafer shows that the PEDOT:PSS retains its capacitive behavior and remains functional after the full process. Once the release step is corrected in the future, the rest of the characterization of the device will be performed. ...
Neural microelectrode arrays (MEAs) are moving from rigid silicon toward soft and transparent substrates, so that electrical recording and optical imaging of the same cells become possible. PDMS is attractive as a substrate because it is soft, biocompatible and transparent, and PEDOT:PSS is attractive as an electrode material because its volumetric capacitance gives a low interface impedance. However, combining the two is difficult in every aspect that matters for microfabrication: surface chemistry, thermomechanical behavior, and compatibility with standard cleanroom steps. Therefore, the process has to be developed rather than adapted from an existing flow. This thesis develops a complete microfabrication process for a transparent PDMS-based MEA with PEDOT:PSS electrodes.
Firstly, we characterized the properties of the individual layers and the PEDOT:PSS/PDMS, metal/PDMS interfaces. Secondly, a full process flow was then built. The main obstacles were micromasking during the PDMS etch, film continuity across the electrode opening, and delamination of the PEDOT:PSS during development, and a solution is presented for each situation. Arrays with 30 µm and 50 µm electrodes were fabricated and prepared for subsequent bonding to a flexible PCB and encapsulation.
At the release step the stack separated at the PDMS/PDMS interface instead of at the base PDMS/SiO2 interface, so the recording face stayed sealed and the electrodes could not be measured individually. However, impedance spectroscopy performed from the front of the wafer shows that the PEDOT:PSS retains its capacitive behavior and remains functional after the full process. Once the release step is corrected in the future, the rest of the characterization of the device will be performed.
Firstly, we characterized the properties of the individual layers and the PEDOT:PSS/PDMS, metal/PDMS interfaces. Secondly, a full process flow was then built. The main obstacles were micromasking during the PDMS etch, film continuity across the electrode opening, and delamination of the PEDOT:PSS during development, and a solution is presented for each situation. Arrays with 30 µm and 50 µm electrodes were fabricated and prepared for subsequent bonding to a flexible PCB and encapsulation.
At the release step the stack separated at the PDMS/PDMS interface instead of at the base PDMS/SiO2 interface, so the recording face stayed sealed and the electrodes could not be measured individually. However, impedance spectroscopy performed from the front of the wafer shows that the PEDOT:PSS retains its capacitive behavior and remains functional after the full process. Once the release step is corrected in the future, the rest of the characterization of the device will be performed.