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Sacrificial adhesive bonding: a powerful method for fabrication of glass microchips.

Lima RS, Leão PA, Piazzetta MH, Monteiro AM, Shiroma LY, Gobbi AL, Carrilho E - Sci Rep (2015)

Bottom Line: This step relies on a selective development to remove the SU-8 only inside the microchannel, generating glass-like surface properties as demonstrated by specific tests.Finally, the SAB protocol is an improvement on SU-8-based bondings described in the literature.Aspects such as substrate/resist adherence, formation of bubbles, and thermal stress were effectively solved by using simple and inexpensive alternatives.

View Article: PubMed Central - PubMed

Affiliation: Laboratório de Microfabricação, Laboratório Nacional de Nanotecnologia, Centro Nacional de Pesquisa em Energia e Materiais, Campinas, São Paulo 13083-970, Brazil.

ABSTRACT
A new protocol for fabrication of glass microchips is addressed in this research paper. Initially, the method involves the use of an uncured SU-8 intermediate to seal two glass slides irreversibly as in conventional adhesive bonding-based approaches. Subsequently, an additional step removes the adhesive layer from the channels. This step relies on a selective development to remove the SU-8 only inside the microchannel, generating glass-like surface properties as demonstrated by specific tests. Named sacrificial adhesive layer (SAB), the protocol meets the requirements of an ideal microfabrication technique such as throughput, relatively low cost, feasibility for ultra large-scale integration (ULSI), and high adhesion strength, supporting pressures on the order of 5 MPa. Furthermore, SAB eliminates the use of high temperature, pressure, or potential, enabling the deposition of thin films for electrical or electrochemical experiments. Finally, the SAB protocol is an improvement on SU-8-based bondings described in the literature. Aspects such as substrate/resist adherence, formation of bubbles, and thermal stress were effectively solved by using simple and inexpensive alternatives.

No MeSH data available.


Related in: MedlinePlus

Microfabrication steps for SAB.Glass slide (a), deposition of SU-8 over this wafer and then pre-bake (b), preliminary bonding against the glass substrate with the walls of the microchannel coated with a thin film of Al (golden in the drawings) (c), cure of the resist just around the microchannel after UV exposure and PEB (resist under the channel is not cured because it is protected from UV by thin film of Al that is deposited only inside the microchannel; see Fig. 4) (d), removal of the uncured SU-8 and, next, of the Al film by pumping specific solvents (blue in the drawing) (e), and final chip showing residual SU-8 in the bottom of the sidewalls (Fig. 6) (f). Features not drawn to scale. In addition, the sidewalls in wet-etched glass are commonly not vertical but rounded.
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f1: Microfabrication steps for SAB.Glass slide (a), deposition of SU-8 over this wafer and then pre-bake (b), preliminary bonding against the glass substrate with the walls of the microchannel coated with a thin film of Al (golden in the drawings) (c), cure of the resist just around the microchannel after UV exposure and PEB (resist under the channel is not cured because it is protected from UV by thin film of Al that is deposited only inside the microchannel; see Fig. 4) (d), removal of the uncured SU-8 and, next, of the Al film by pumping specific solvents (blue in the drawing) (e), and final chip showing residual SU-8 in the bottom of the sidewalls (Fig. 6) (f). Features not drawn to scale. In addition, the sidewalls in wet-etched glass are commonly not vertical but rounded.

Mentions: Herein, we present a new bonding method for fabricating glass microchips, named sacrificial adhesive bonding (SAB). The procedure is simple, fast, and compatible with ULSI processes and thin film integration. First, it consists of using an intermediate layer to seal glass slides to one another, as in conventional adhesive bonding. However, this intermediate layer is selectively developed (and removed) to create microfluidic channels with glass-like surface properties. In this procedure, a specific developer flows with the aid of a hydrodynamic pumping system removing the intermediate just inside the microfluidic channel. The main steps of the microfabrication in SAB are depicted in Fig. 1. SU-8 resist was used as sacrificial adhesive. Such a thermoset is a fundamental element of pattern transfer processes obtained by photolithography. The advantages of this epoxy-based negative photoresist are: (1) thermomechanical stability, (2) chemical inertia (resistance to organic media and alkaline or acid solutions at high temperature), (3) transparency (near UV and visible radiation), (4) sensitivity, selectivity, and contrast to UV, (5) photolithography resolution, (6) biocompatibility, (7) vertical sidewall profile (desired for lift-off), (8) wide range of thickness (1 to approximately 500 μm) achieved by spinning in a single run3, and (9) electrophoretic performance similar to that of glass24. Additionally, uncross-linked SU-8 is used as glue in adhesive bonding processes. All-SU-8 microdevices are reported in the literature as well. The latter require a multilevel photolithography for fabrication that defines the bottom, sidewall, and top surfaces in SU-825.


Sacrificial adhesive bonding: a powerful method for fabrication of glass microchips.

Lima RS, Leão PA, Piazzetta MH, Monteiro AM, Shiroma LY, Gobbi AL, Carrilho E - Sci Rep (2015)

Microfabrication steps for SAB.Glass slide (a), deposition of SU-8 over this wafer and then pre-bake (b), preliminary bonding against the glass substrate with the walls of the microchannel coated with a thin film of Al (golden in the drawings) (c), cure of the resist just around the microchannel after UV exposure and PEB (resist under the channel is not cured because it is protected from UV by thin film of Al that is deposited only inside the microchannel; see Fig. 4) (d), removal of the uncured SU-8 and, next, of the Al film by pumping specific solvents (blue in the drawing) (e), and final chip showing residual SU-8 in the bottom of the sidewalls (Fig. 6) (f). Features not drawn to scale. In addition, the sidewalls in wet-etched glass are commonly not vertical but rounded.
© Copyright Policy - open-access
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC4543966&req=5

f1: Microfabrication steps for SAB.Glass slide (a), deposition of SU-8 over this wafer and then pre-bake (b), preliminary bonding against the glass substrate with the walls of the microchannel coated with a thin film of Al (golden in the drawings) (c), cure of the resist just around the microchannel after UV exposure and PEB (resist under the channel is not cured because it is protected from UV by thin film of Al that is deposited only inside the microchannel; see Fig. 4) (d), removal of the uncured SU-8 and, next, of the Al film by pumping specific solvents (blue in the drawing) (e), and final chip showing residual SU-8 in the bottom of the sidewalls (Fig. 6) (f). Features not drawn to scale. In addition, the sidewalls in wet-etched glass are commonly not vertical but rounded.
Mentions: Herein, we present a new bonding method for fabricating glass microchips, named sacrificial adhesive bonding (SAB). The procedure is simple, fast, and compatible with ULSI processes and thin film integration. First, it consists of using an intermediate layer to seal glass slides to one another, as in conventional adhesive bonding. However, this intermediate layer is selectively developed (and removed) to create microfluidic channels with glass-like surface properties. In this procedure, a specific developer flows with the aid of a hydrodynamic pumping system removing the intermediate just inside the microfluidic channel. The main steps of the microfabrication in SAB are depicted in Fig. 1. SU-8 resist was used as sacrificial adhesive. Such a thermoset is a fundamental element of pattern transfer processes obtained by photolithography. The advantages of this epoxy-based negative photoresist are: (1) thermomechanical stability, (2) chemical inertia (resistance to organic media and alkaline or acid solutions at high temperature), (3) transparency (near UV and visible radiation), (4) sensitivity, selectivity, and contrast to UV, (5) photolithography resolution, (6) biocompatibility, (7) vertical sidewall profile (desired for lift-off), (8) wide range of thickness (1 to approximately 500 μm) achieved by spinning in a single run3, and (9) electrophoretic performance similar to that of glass24. Additionally, uncross-linked SU-8 is used as glue in adhesive bonding processes. All-SU-8 microdevices are reported in the literature as well. The latter require a multilevel photolithography for fabrication that defines the bottom, sidewall, and top surfaces in SU-825.

Bottom Line: This step relies on a selective development to remove the SU-8 only inside the microchannel, generating glass-like surface properties as demonstrated by specific tests.Finally, the SAB protocol is an improvement on SU-8-based bondings described in the literature.Aspects such as substrate/resist adherence, formation of bubbles, and thermal stress were effectively solved by using simple and inexpensive alternatives.

View Article: PubMed Central - PubMed

Affiliation: Laboratório de Microfabricação, Laboratório Nacional de Nanotecnologia, Centro Nacional de Pesquisa em Energia e Materiais, Campinas, São Paulo 13083-970, Brazil.

ABSTRACT
A new protocol for fabrication of glass microchips is addressed in this research paper. Initially, the method involves the use of an uncured SU-8 intermediate to seal two glass slides irreversibly as in conventional adhesive bonding-based approaches. Subsequently, an additional step removes the adhesive layer from the channels. This step relies on a selective development to remove the SU-8 only inside the microchannel, generating glass-like surface properties as demonstrated by specific tests. Named sacrificial adhesive layer (SAB), the protocol meets the requirements of an ideal microfabrication technique such as throughput, relatively low cost, feasibility for ultra large-scale integration (ULSI), and high adhesion strength, supporting pressures on the order of 5 MPa. Furthermore, SAB eliminates the use of high temperature, pressure, or potential, enabling the deposition of thin films for electrical or electrochemical experiments. Finally, the SAB protocol is an improvement on SU-8-based bondings described in the literature. Aspects such as substrate/resist adherence, formation of bubbles, and thermal stress were effectively solved by using simple and inexpensive alternatives.

No MeSH data available.


Related in: MedlinePlus