High-density CMOS probes for large-scale extracellular neural recording

Abstract: In order to move forward with understanding the brain, many challenges have to be addressed. On the experimental side, these include performing simultaneous large-scale recordings from different brain regions and processing neural signals in close proximity to their firing sources. For this reason, minimizing the size of recording tools while increasing their performance remains an essential goal of research in neurotechnology.

This thesis presents the design, fabrication and characterization of two neural probe systems developed to serve some of the current neuroscientist research goals. Both systems implement the electronic depth control approach which provides substantial flexibility in monitoring different brain regions without moving the probe within the brain. The probe systems have been realized in a 0.18 µm complementary metal-oxide semiconductor (CMOS) technology which is followed by a customized microfabrication process performed at the Clean Room Service Center of the Department of Microsystems Engineering. The post-CMOS process involves a series of steps to deposit passivation and metallization layers and to pattern the deposited and the subjacent CMOS layers.

The first system presented in this thesis implements a new hierarchical addressing scheme distributed across the entire probe structure. As a consequence, the decoding and selection process of recording sites is performed at the probe base and in the slender shank which consists of 50 identical blocks of 32 electrodes each. The implemented addressing scheme has resulted in an area-efficient array of 1600 recording sites, with a footprint of 17×17 µm² per electrode, integrated along a 10-mm-long, 100-µm-wide and 50-µm-thick probe shank. The compact and dense arrangement of the recording sites with an electrode-to-electrode spacing of 3 µm allows neuroscientists to perform recordings with high spatial resolution. Up to 32 recording sites can be recorded simultaneously using analog output channels. In addition, the probe system provides the capability to reconfigure the set of selected electrodes within a short time period of around 33 µs. The probe base has a small area of 0.55×1.8 µm² which facilitates performing in vivo experiments and increases the number of fabricated probes per wafer.

The functionality of the addressing scheme and the fabricated probes has been validated. The electrochemical impedances of platinum and iridium oxide electrodes were measured to be 2.2±0.28 MΩ and 231±39 kΩ, respectively. Also, a crosstalk of -58 dB at 1 kHz was measured between two adjacent output channels. In addition, in vivo acute experiments were successfully conducted to measure brain activity of anesthetized rats. In this experiment, the electrodes were reconfigured to monitor multiple regions located at different depths in the brain.

The second neural probe system presented in this thesis comprises 128 recording sites with an area-efficient low-noise amplifier (LNA), with a footprint of 45×78 µm², integrated under each electrode. The probe uses the same addressing scheme concept implemented in the first system. Here, the 100-µm-wide and 7-mm-long probe shank is divided into 16 blocks of eight electrodes each. The topology used to implement the LNA integrated in each recording site is a single stage differential cascode amplifier with improvements implemented to enhance the system performance. The LNA has been realized in two feedback versions with different low cut-off frequencies.

The system functionality has been verified using test chips designed to characterize the LNA performance as well as using the fabricated probe system. The closed-loop gain of the fabricated LNA was measured to be 35–37 dB. Also, the low cut-off frequency is 0.35 Hz and 130 Hz for the two feedback versions, while the high cut-off is around 9 kHz. The resulting input-referred noise of the fabricated LNA is 16 µVrms in the frequency range of 200 Hz–5 kHz and 22 µVrms for the frequency band between the lower and the upper cut-off frequencies. The power consumption of the LNA is 7.7 µW at a supply voltage of ±0.9 V.

Object Details

• Location: Deutsche Nationalbibliothek Frankfurt am Main
• Extent: Online-Ressource
• Language: Englisch
• Notes: Universität Freiburg, Dissertation, 2020

Classification and Topics

• Keyword: Sonde ; Schnittstelle

Contributors, Places and Time

• Event: Veröffentlichung
• (where): Freiburg
• (who): Universität
• (when): 2021
• Creator: Sayed Herbawi, Abdalrahman
• Contributor: Paul, Oliver ; Albert-Ludwigs-Universität Freiburg. Fakultät für Angewandte Wissenschaften

Further information

• DOI: 10.6094/UNIFR/175792
• URN: urn:nbn:de:bsz:25-freidok-1757925
• Rights: Der Zugriff auf das Objekt ist unbeschränkt möglich.
• Last update: 25.03.2025, 1:51 PM CET