Sacrificial Layer Technique for Releasing Metallized Multilayer SU-8 Devices

Abstract

The low fabrication cost of SU-8-based devices has opened the fields of point-of-care devices (POC), µTAS and Lab-on-Chip technologies, which call for cheap and disposable devices. Often this translates to free-standing, suspended devices and a reusable carrier wafer. This necessitates a sacrificial layer to release the devices from the substrates. Both inorganic (metals and oxides) and organic materials (polymers) have been used as sacrificial materials, but they fall short for fabrication and releasing multilayer SU-8 devices. We propose photoresist AZ 15nXT (MicroChemicals GmbH, Ulm, Germany) to be used as a sacrificial layer. AZ 15nXT is stable during SU-8 processing, making it suitable for fabricating free-standing multilayer devices. We show two methods for cross-linking AZ 15nXT for stable sacrificial layers and three routes for sacrificial release of the multilayer SU-8 devices. We demonstrate the capability of our release processes by fabrication of a three-layer free-standing microfluidic electrospray ionization (ESI) chip and a free-standing multilayer device with electrodes in a microchannel.

An innovative methodology for monitoring the sacrificial layer removal process in MEMS structures

“…The basic requirements for the sacrificial layer technique include chemical/thermal/mechanical stability during subsequent processing steps, easy deposition and patterning, and selective removal (in comparison to structural layers) during the release step [11]. Also, an essential parameter for high throughput in a production line is the sacrificial layer releasing time [12].…”

“…The AZ 4620 photoresist sacrificial layer was dissolved by the SU-8 developer (propylene glycol monomethyl ether acetate) [19]. Also, in 2018 Anand Tatikonda et al proposes the use of photoresist AZ 15nXT as a stable sacrificial layer for the low-cost fabrication of multilayer SU-8-based devices, enabling the creation of free-standing microfluidic electrospray ionization (ESI) chips and multilayer devices with electrodes in microchannels through innovative release processes [11].…”

Fabrication of a 3D high-resolution implant for neural stimulation - challenges and solutions

“…As a conceptual device, we fabricated a sub-retinal implant composed of gold electrodes deposited on epoxy SU-8 as a substrate material, which is widely used in diverse bio-micro-electromechanical system (bio-MEMS) elds due to its mechanical properties and high aspect ratio capabilities. The fabrication process of a free-standing (11,12) complex 3D (13)(14)(15) metal coated (16, 17) bio-electronic device (15,(18)(19)(20)(21)(22) poses many challenges. Among the speci c main challenges are the creation of 3D structures with a high aspect ratio (14,23)and high-resolution, the shaping of metal microelectrode edges while avoiding "ear patterning", the fabrication of high-density metal microelectrodes with strong adhesion to SU-8, proper releasing of the device, and the bio-functionalization of the electrodes and encapsulation, aiming to enhance cell adhesion.…”

Synthesis of Printable Polyvinyl Alcohol for Aerosol Jet and Inkjet Printing Technology

“…Along with developing printed technology, researchers have been working on selecting appropriate sacrificial materials for years. In [ 39 ], the use of sacrificial layer technique is discussed to create multilayer metalized structure using SU-8 dielectric. Multilayer suspended structure was successfully fabricated by adopting sputter coating, which is another form of solution processible technique.…”