以微機電技術製造應用於大腦皮質層電波量測之可撓式平面電極

Abstract

本論文研究以微機電技術發展以聚對二甲苯(Parylene C)為基材可應用於大腦皮質層電波感測之可撓式平面電極元件的製造，製程上利用厚度10um基材搭配厚度1um元件保護層成功製作出上薄下厚三明治結構(上下二層Parylene；中間一層白金)，改善目前以聚酰亞胺(Polyimide)製作的對稱三明治結構平面電極，其相同之基材及元件保護層厚度(>20um)將造成平面電極柔軟度差而無法有效貼附在大腦皮質層上，另外元件保護層厚度將造成電極與感測區域落差大而需另外電鍍電極等後製程問題。此外，Parylene可於室溫下鍍膜，改善Polyimide製作上需利用高溫(200~400℃) curing而改變原先基材厚度的缺點。最後，本研究提出之平面電極經由測試，動物實驗量測到聽覺皮層誘發電位約為±70μV，在麻醉狀態下引起誘發電位的最小聲音強度為20dB SPL，且亦可偵測到大腦局部神經群放電效應GAMA Activity (30Hz ~ 500Hz)。結果顯示此電極陣列不僅涵蓋大部份聽覺皮層且可分出不同聽覺分區。未來將可進一步應用在清醒動物上，有助於探討神經可塑性與腦部疾病發生之機制及其致病原因，亦可發展以大腦腦電波控制的新一代腦機介面。

In this thesis, the implementation and characterization of a MEMS-based flexible surface electrode utilizing parylene-C as substrate was presented for ECoG measurement applications. An un-symmetric sandwich-type structure consists of two parylene layer (10um substrate & 1um isolation layer) and one platinum layer was successfully realized in this study. Comparing to previous works that using symmetric sandwich-type structures and thicker isolation layer (polyimide, >20um), proposed method enhanced the adhesion property on brain cortex surface with great flexibility. Also, previous works may suffer from the level difference between sensing electrode and sensor surface due to the thick isolation layer and need another electroplating post process. By applying the proposed method, simplified process and superior properties were achieved without extra complex post processes. Furthermore, comparing to polyimide process that needs curing temperature (200~400℃) which cause thickness variation, presented method can be accomplished under room temperature. Practical in-vivo experiments demonstrate the recording capability of the proposed surface electrode array. Recorded auditory evoked potentials (AEPs) is ±70μV with 20dB SPL minimum sound level under general anesthesia, as well as the localized neurons discharge phenomenon (GAMA Activity, 30Hz~500Hz). The measurement result shows that the presented electrode array can cover the most of brain auditory cortex surface area, and distinguish specific signal characteristics between different electrode sites. Proposed multi-electrode array can be used in awake animals in the future works, help the studies on neurons degeneration, the mechanism of brain disease, and the development of the ECoG controlled BCI interface as well.