Micropatterning of poly(dimethylsiloxane) using a photoresist lift-off technique for selective electrical insulation of microelectrode arrays

Abstract

A poly(dimethylsiloxane) (PDMS) patterning method based on a photoresist lift-off technique to make an electrical insulation layer with selective openings is presented. The method enables creating PDMS patterns with small features and various thicknesses without any limitation in the designs and without the need for complicated processes or expensive equipments. Patterned PDMS layers were created by spin-coating liquid phase PDMS on top of a substrate having sacrificial photoresist patterns, followed by a photoresist lift-off process. The thickness of the patterned PDMS layers could be accurately controlled (6.5–24 µm) by adjusting processing parameters such as PDMS spin-coating speeds, PDMS dilution ratios, and sacrificial photoresist thicknesses. PDMS features as small as 15 µm were successfully patterned and the effects of each processing parameter on the final patterns were investigated. Electrical resistance tests between adjacent electrodes with and without the insulation layer showed that the patterned PDMS layer functions properly as an electrical insulation layer. Biocompatibility of the patterned PDMS layer was confirmed by culturing primary neuron cells on top of the layer for up to two weeks. An extensive neuronal network was successfully formed, showing that this PDMS patterning method can be applied to various biosensing microdevices. The utility of this fabrication method was further demonstrated by successfully creating a patterned electrical insulation layer on flexible substrates containing multi-electrode arrays.

A PDMS-Based Conical-Well Microelectrode Array for Surface Stimulation and Recording of Neural Tissues

“…Thus, most negative photoresists are not suitable in our process due to their difficulty in stripping after development without using solvents, with the exception that a compatible stripper exists (e.g. RR4 or RR41 from Futurrex for its NR series, as has been used in [27]). Considering these, we focused on developing an efficient, high-resolution lift-off method using a positive photoresist with its developer as the stripper.…”

“…After exploration, we finally found the negative photoresist NR5-8000 (Futurrex, Inc.) could meet all the above requirements. Results also show that, with proper process parameters, planar electrodes could be fabricated [27], [28], [45]. …”

“…The combination of spin speed, spin duration, and baking conditions is designed to disperse the prepolymer to a film thickness less than the height of the sacrificial posts [26]. Additionally, the processing recipe guarantees that the prepolymer gets rid of the top of sacrificial posts [27], [28]. These conditions and the oxygen plasma pre-treatment are crucial for successfully achieving the conical-well structure.…”

Elastomer Application in Microsystem and Microfluidics

“…Recently, PDMS has been micropatterned using a photoresist lift-off technique for selective electrical insulation in microelectrode array applications 39 . The micropatterning technique is able to manufacture PDMS patterns with feature as small as 15 µm and various thicknesses down to 6 µm.…”

Simulation of polymeric integrated Young interferometer sensor

“…As cladding, PDMS layer is considered, both for its compatibility with the microfluidic channel fabrication and for its lower refractive index compared to SU8 (n SU8 =1.61 and n PDMS = 1.43). Although PDMS cannot be directly patterned by photolithography, there are some methods for PDMS configuration with the usual photolithographic techniques with additional technological steps 6,7 The medium refractive index change are recorded by monitoring the the shift of the interference fringe at a certain distance from the sensor exit facet. The fringe shift appear s due to the change in the radiation phase difference between the reference and the measurement arm.…”