BETTS: bonding, exposing and transferring technique in SU-8 for microsystems fabrication

Abstract

A novel fabrication process called BETTS (bonding, UV exposing and transferring technique in SU-8) is presented in this paper. SU-8 layers can be transferred and patterned over SU-8 microstructures by means of a removable, flexible and transparent substrate. This substrate is composed of a thin acetate film, which can be also used as a mask, and a cured PDMS layer deposited over it. SU-8 is then spin coated and transferred to the SU-8 structures performing simultaneously the steps of bonding and transferring by UV exposure. Due to the low adhesion between PDMS and SU-8, acetate film removal can be easily performed. BETTS provides easy, irreversible and robust SU-8 to SU-8 bonding, where the absence of oxygen plasma equipment or vacuum systems decreases drastically the fabrication cost and time involved. The reported fabrication process makes it possible to fabricate complex SU-8 three-dimensional structures using a simple and inexpensive procedure and also ensures its compatibility and integration with microfluidic and PCB-MEMS devices. Some specific applications such as multilevel microchannel network, patterned membranes, microchambers and microvalves are reported to demonstrate the potential of the proposed process.

Electroosmotic impulsion device for integration in PCB-MEMS

“…Next, in step 7, the inlet and outlet ports are drilled. Later, in step 8, an SU-8 cover is transferred and bonded using BETTS [15] in order to construct buried microchannels, finishing the fabrication of the micropump. The procedure of fabrication can be seen in Fig.…”

Fabrication process of a SU-8 monolithic pressurized microchamber for pressure driven microfluidic applications

“…Now, a 50 µm layer (SU-8 2025) is spinned over an acetate sheet with a thickness of 180 µm, which was previously cleaned with IPA. After drilling dust removal, the device is covered by a similar procedure to BETTS [7] without PDMS and acetate removal, in order to make the fabrication process faster (h). The thickness of the SU-8 layer over the acetate is selected to avoid undesirable displacements into the cavities of the resist in contact with the device walls, and specifically to prevent the control microchannel from obstruction.…”

“…In addition to this, new fabrication processes such as BETTS (Bonding, UV Exposing and Transferring Technique in SU-8) [7] have been developed and successfully demonstrated, making faster and easier the adhesive bonding of SU-8 membranes over a wide range of materials to achieve hermetically sealed microfluidic cavities. Although polymers are typically several orders of magnitude more permeable to gas leakages than glass or metals, epoxy resins are characterized by low gas permeability and thus can be used for simple and low-cost sealing of packages [8].…”

Glass/SU‐8 microchip for electrokinetic applications

“…SU‐8 is an epoxy‐based negative photoresist fundamental at photolithographic pattern transfers . In addition, this resist has been used in the fabrication of microfluidic channels , reactors , cantilevers , photonic crystals , solar and fuel cells, and microchip CE‐ESI for MS . Other applications involve the integration of sensors , electrochemical detectors , MEM components , optical waveguides , molecular filters , PCR analyzers , chromatography separation phases , and dielectrophoresis system .…”

“…This releasing step is necessary to access the reservoirs that are recorded in the resist top surface. Hydrofluoric acid (HF) etching , mechanical process using a carrier surface with low adhesion to SU‐8 , and resist lift‐off list as some of the procedures employed for the releasing step in microfluidics. The etching‐based release can take 12 h when using interfaces with high thermal stress .…”