Advances in Encapsulating Elastically Stretchable Microelectrode Arrays
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Advances in Encapsulating Elastically Stretchable Microelectrode Arrays Oliver Graudejus1, Candice Tsay1, Sigurd Wagner1, Zhe Yu2, Barclay Morrison III2, and Stephanie Lacour3 1 Electrical Engineering, Princeton University, Engineering Quadrangle, Olden Street, Princeton, NJ, 08544 2 Biomedical Engineering, Columbia University, 351 Engineering Terrace, MC 8904, 1210 Amsterdam Avenue, New York, NY, 10027 3 Material Science, Cambridge University, Cambridge, CB2 3QZ, United Kingdom
ABSTRACT Stretchable microelectrode arrays (SMEAs) that are fabricated on the compliant silicone poly dimethyl siloxane (PDMS) have potential applications for research on traumatic brain injury (TBI). Increasing the number of electrodes in the array improves the accuracy in assessing the effects of traumatic injury to cell tissue cultures. The currently available encapsulation process with a photopatternable silicone limits the electrode density on the array. The present research examines four factors in the encapsulation process: exposure dose, scattered and reflected light as well as hard bake time. Careful optimization of these four factors leads to a significant reduction of the minimum feature size of a contact via patterned into the encapsulation layer, thus enabling an increase of the electrode density on the array. INTRODUCTION About 50,000 Americans die of traumatic brain injury (TBI) each year. In addition, about 1.4 million Americans sustain a traumatic brain injury every year and currently five million Americans who suffered from a traumatic brain injury require lifelong care. The annual direct and indirect costs of TBI are estimated to be 60 billion dollars in the U.S. alone [1]. Minimizing the consequences of TBI would greatly benefit the affected individuals and the society. The present research focuses on fabricating a stretchable microelectrode array (SMEA) for an in-vitro TBI model [2]. Stretchable thin-film metallization could provide a mechanically compliant interface with the neural tissue used for the study of traumatic brain injury [3]. In addition, stretchable metallization may enable elastically stretchable metal interconnects for electronic skin [4, 5]. The basic structure of elastic thin-film metallization is (i) an elastomeric substrate, (ii) a thin-film metallization patterned as needed by the application, (iii) an overlayer of stretchable encapsulation and electrical insulation, and (iv) vias made in the encapsulation for contacts. Encapsulating the electrodes and opening contact vias are critical steps in fabricating the SMEAs. These steps currently limit the minimum feature size and therefore the electrode density. In this paper we describe how the resolution of the encapsulation can be improved, allowing the electrode density to be increased. We apply a photopatternable silicone for electrode encapsulation and then pattern it for contact vias. We have increased the resolution of the SMEAs by optimizing four factors in the
encapsulation process: exposure dose, minimizing scattered and reflected
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