Evaluation of bonding between oxygen plasma treated polydimethyl siloxane and passivated silicon
01 Apr 2006-Vol. 34, Iss: 1, pp 155-161
TL;DR: In this article, the bonding quality of polydimethyl siloxane to passivated silicon using oxygen plasma treatment was evaluated using manual peel and mechanical shear tests, and it was found that the lowering of plasma pressure from 500 to 30 mTorr and using a plasma power between 20 to 60 W helped to improve the bond quality for the first three types of passivation.
Abstract: Oxygen plasma treatment has been used extensively to bond polydimethyl siloxane to polydimethyl siloxane or glass in the rapid prototyping of microfluidic devices. This study aimed to improve the bonding quality of polydimethyl siloxane to passivated silicon using oxygen plasma treatment, and also to evaluate the bonding quality. Four types of passivated silicon were used: phosphosilicate glass, undoped silicate glass, silicon nitride and thermally grown silicon dioxide. Bonding strength was evaluated qualitatively and quantitatively using manual peel and mechanical shear tests respectively. Through peel tests we found that the lowering of plasma pressure from 500 to 30 mTorr and using a plasma power between 20 to 60 W helped to improve the bond quality for the first three types of passivation. Detailed analysis and discussion were conducted to explain the discrepancy between the bonding strength results and peeling results. Our results suggested that polydimethyl siloxane can be effectively bonded to passivated silicon, just as to polydimethyl siloxane or glass.
Citations
More filters
TL;DR: Critical selection criteria are included for pumps and valves to aid in determining the pumping mechanism that is most appropriate for a given application and important limitations or incompatibilities are addressed.
Abstract: Micropumping has emerged as a critical research area for many electronics and biological applications. A significant driving force underlying this research has been the integration of pumping mechanisms in micro total analysis systems and other multi-functional analysis techniques. Uses in electronics packaging and micromixing and microdosing systems have also capitalized on novel pumping concepts. The present work builds upon a number of existing reviews of micropumping strategies by focusing on the large body of micropump advances reported in the very recent literature. Critical selection criteria are included for pumps and valves to aid in determining the pumping mechanism that is most appropriate for a given application. Important limitations or incompatibilities are also addressed. Quantitative comparisons are provided in graphical and tabular forms.
467 citations
Cites background from "Evaluation of bonding between oxyge..."
...An O2 plasma etch of PDMS surfaces converts the surface O– Si(CH3)2 group into a silanol (OH) group which, in turn, changes the surface chemistry from hydrophobic to hydrophilic (Tang et al. 2006)....
[...]
TL;DR: This work describes the real-time detection of single magnetically labelled cells with a magnetoresistive based cell cytometer and compares that obtained with a hemocytometer.
Abstract: Although conventional state-of-the-art flow cytometry systems provide rapid and reliable analytical capacities, they are bulky, expensive and complex. To overcome these drawbacks modern flow cytometers have been developed with enhanced portability for on-site measurements. Unlike external fluorescent/optical detectors, magnetoresistive sensors are micro-fabricated, can be integrated within microfluidic channels, and can detect magnetically labelled cells. This work describes the real-time detection of single magnetically labelled cells with a magnetoresistive based cell cytometer. For Kg1-a cells magnetically labelled with 50 nm CD34 microbeads (Milteny) flowing through a 150 μm wide, 14 μm high microchannel, with speeds around 1 cm s−1, bipolar signals with an average amplitude of 10–20 μV were observed corresponding to cell events. The number of cells counted by the spin valve cytometer has been compared with that obtained with a hemocytometer. Both methods agree within the respective error bars.
68 citations
TL;DR: In this article, a modified poly-dimethyl-siloxane (PDMS) soft stamp was used to reduce pattern deformation and residual layer thickness in soft UV-nanoimprint lithography.
57 citations
TL;DR: In this paper, the authors presented a comprehensive experimental study and characterization of material and bonding of PDMS-based structures to various substrates, including semiconductor substrates (silicon, zinc oxide, and silicon dioxide), metals (gold, aluminum), photoresists (SU-8, AZxx) and glass.
Abstract: This paper presents a comprehensive experimental study and characterization of material and bonding of PDMS based structures to various substrates. A previously published method [1] of bonding is further improved with the inclusion of more substrate material and additional characteristics. Uncured PDMS is used as an adhesive to bond PDMS devices reversibly to various substrates including a number of commonly used substrate materials that are not supported by the widely used plasma treatment method. We have optimized parameters such as PDMS base to curing agent ratio, curing temperature, and PDMS device age to obtain better bond strengths and quality. Bond strengths are presented for semiconductor substrates (silicon, zinc oxide, and silicon dioxide), metals (gold, aluminum), photoresists (SU-8, AZxx) and glass. Silicon based substrates experienced minor amounts of surface residue, but the method is fully reversible for other tested substrates. Bond strengths were measured as maximum endurable pressure between PDMS and substrates. Maximum average bond strengths of more than 0.4 MPa were achieved for substrates with Si-O groups. Other substrates exhibited maximum average bond strengths in the range 0.2–0.3 MPa. Also presented is a method that avoids alignment step for PDMS microfluidic device bonding, named the non-aligned method. This method provides bond strengths of more than 0.1 MPa. Presented methods do not need special equipment or processes such as plasma generators or temperature increases. Biocompatibility tests are performed for materials used in fabrications to ensure applicability in bio-sensing related devices.
52 citations
TL;DR: A flexible, color-neutral, and high-efficiency transparent solar cell based on a freestanding form of n-silicon microwires embedded in a transparent polymer matrix is demonstrated and the stretchable and transparent platform in this study is promising for future TSCs.
Abstract: Transparent solar cells (TSCs) are emerging devices that combine the advantages of visible transparency and light-to-electricity conversion. Currently, existing TSCs are based predominantly on organics, dyes, and perovskites; however, the rigidity and color-tinted transparent nature of those devices strongly limit the utility of the resulting TSCs for real-world applications. Here, we demonstrate a flexible, color-neutral, and high-efficiency TSC based on a freestanding form of n-silicon microwires (SiMWs). Flat-tip SiMWs with controllable spacing are fabricated via deep-reactive ion etching and embedded in a freestanding transparent polymer matrix. The light transmittance can be tuned from ~10 to 55% by adjusting the spacing between the microwires. For TSCs, a heterojunction is formed with a p-type polymer in the top portion of the n-type flat-tip SiMWs. Ohmic contact with an indium-doped ZnO film occurs at the bottom, and the side surface has an Al2O3 passivation layer. Furthermore, slanted-tip SiMWs are developed by a novel solvent-assisted wet etching method to manipulate light absorption. Finite-difference time-domain simulation revealed that the reflected light from slanted-tip SiMWs helps light-matter interactions in adjacent microwires. The TSC based on the slanted-tip SiMWs demonstrates 8% efficiency at a visible transparency of 10% with flexibility. This efficiency is the highest among Si-based TSCs and comparable with that of state-of-the-art neutral-color TSCs based on organic-inorganic hybrid perovskite and organics. Moreover, unlike others, the stretchable and transparent platform in this study is promising for future TSCs.
48 citations
References
More filters
TL;DR: Fabrication of microfluidic devices in poly(dimethylsiloxane) (PDMS) by soft lithography provides faster, less expensive routes to devices that handle aqueous solutions.
Abstract: Microfluidic devices are finding increasing application as analytical systems, biomedical devices, tools for chemistry and biochemistry, and systems for fundamental research. Conventional methods of fabricating microfluidic devices have centered on etching in glass and silicon. Fabrication of microfluidic devices in poly(dimethylsiloxane) (PDMS) by soft lithography provides faster, less expensive routes than these conventional methods to devices that handle aqueous solutions. These soft-lithographic methods are based on rapid prototyping and replica molding and are more accessible to chemists and biologists working under benchtop conditions than are the microelectronics-derived methods because, in soft lithography, devices do not need to be fabricated in a cleanroom. This paper describes devices fabricated in PDMS for separations, patterning of biological and nonbiological material, and components for integrated systems.
3,344 citations
"Evaluation of bonding between oxyge..." refers background in this paper
...Introduction In microfluidic applications, polydimethyl siloxane (PDMS) is a popular type of polymer used in the rapid prototyping of microfluidic systems [1,2]....
[...]
...In addition, a thin layer of PDMS can also be used as a capping layer for microfluidic devices as it is optically transparent down to 280 nm and thus suitable for a number of fluorescence or absorbance detection schemes [1]....
[...]
TL;DR: This Account summarizes techniques for fabrication and applications in biomedicine of microfluidic devices fabricated in poly(dimethylsiloxane) (PDMS).
Abstract: This Account summarizes techniques for fabrication and applications in biomedicine of microfluidic devices fabricated in poly(dimethylsiloxane) (PDMS). The methods and applications described focus on the exploitation of the physical and chemical properties of PDMS in the fabrication or actuation of the devices. Fabrication of channels in PDMS is simple, and it can be used to incorporate other materials and structures through encapsulation or sealing (both reversible and irreversible).
2,490 citations
"Evaluation of bonding between oxyge..." refers background or methods in this paper
...Introduction In microfluidic applications, polydimethyl siloxane (PDMS) is a popular type of polymer used in the rapid prototyping of microfluidic systems [1,2]....
[...]
...After placing the two pieces together the specimens were treated in an oven at 150 ̊C for 2 h with a weight placed on it to improve the bond strength [2]....
[...]
TL;DR: The focus of this review is microscale phenomena and the use of the physics of the scale to create devices and systems that provide functionality useful to the life sciences.
Abstract: ■ Abstract Fluid flow at the microscale exhibits unique phenomena that can be leveraged to fabricate devices and components capable of performing functions useful for biological studies. The physics of importance to microfluidics are reviewed. Common methods of fabricating microfluidic devices and systems are described. Components, including valves, mixers, and pumps, capable of controlling fluid flow by utilizing the physics of the microscale are presented. Techniques for sensing flow characteristics are described and examples of devices and systems that perform bioanalysis are presented. The focus of this review is microscale phenomena and the use of the physics of the scale to create devices and systems that provide functionality useful to the life sciences.
1,721 citations
"Evaluation of bonding between oxyge..." refers background in this paper
...Consequently, this means that the fluidic pressure exerted in the fluidic channels are inversely proportional to its cross-sectional length scale by four orders [4]....
[...]
TL;DR: In this article, a fabrication technique for building 3D micro-channels in polydimethylsiloxane (PDMS) elastomer is described, which allows for the stacking of many thin (less than 100-/spl mu/m) patterned PDMS layers to realize complex 3D channel paths.
Abstract: This paper describes a fabrication technique for building three-dimensional (3-D) micro-channels in polydimethylsiloxane (PDMS) elastomer. The process allows for the stacking of many thin (less than 100-/spl mu/m thick) patterned PDMS layers to realize complex 3-D channel paths. The master for each layer is formed on a silicon wafer using an epoxy-based photoresist (SU 8). PDMS is cast against the master producing molded layers containing channels and openings. To realize thin layers with openings, a sandwich molding configuration was developed that allows precise control of the PDMS thickness. The master wafer is clamped within a sandwich that includes flat aluminum plates, a flexible polyester film layer, a rigid Pyrex wafer, and a rubber sheet. A parametric study is performed on PDMS surface activation in a reactive-ion-etching system and the subsequent methanol treatment for bonding and aligning very thin individual components to a substrate. Low RF power and short treatment times are better than high RF power and long treatment times, respectively, for instant bonding. Layer-to-layer alignment of less then 15 /spl mu/m is achieved with manual alignment techniques that utilize surface tension driven self-alignment methods. A coring procedure is used to realize off-chip fluidic connections via the bottom PDMS layer, allowing the top layer to remain smooth and flat for complete optical access.
1,200 citations
"Evaluation of bonding between oxyge..." refers background or result in this paper
...Oxygen plasma treatment has been used by many researchers to create an effective bonding of PDMS to PDMS or glass [5,6]....
[...]
...Besides higher plasma power, an over-exposure to plasma is detrimental to the adhesiveness of PDMS to all the passivation materials, which has also been reported in previous literatures [5,6]....
[...]
TL;DR: In this article, the authors explored the possibility of the existence of a common scale, which can be used to gauge bond strength between various surfaces and found that the changes in wettability of surfaces owing to various levels of plasma exposure can be a useful parameter to gauge the bond strength.
Abstract: An issue in microfabrication of the fluidic channels in glass/poly (dimethyl siloxane) (PDMS) is the absence of a well-defined study of the bonding strength between the surfaces making up these channels. Although most of the research papers mention the use of oxygen plasma for developing chemical (siloxane) bonds between the participating surfaces, yet they only define a certain set of parameters, tailored to a specific setup. An important requirement of all the microfluidics/biosensors industry is the development of a general regime, which defines a systematic method of gauging the bond strength between the participating surfaces in advance by correlation to a common parameter. This enhances the reliability of the devices and also gives a structured approach to its future large-scale manufacturing. In this paper, we explore the possibility of the existence of a common scale, which can be used to gauge bond strength between various surfaces. We find that the changes in wettability of surfaces owing to various levels of plasma exposure can be a useful parameter to gauge the bond strength. We obtained a good correlation between contact angle of deionized water (a direct measure of wettability) on the PDMS and glass surfaces based on various dosages or oxygen plasma treatment. The exposure was done first in an inductively coupled high-density (ICP) plasma system and then in plasma enhanced chemical vapor deposition (PECVD) system. This was followed by the measurement of bond strength by use or the standardized blister test.
825 citations
"Evaluation of bonding between oxyge..." refers background or result in this paper
...Oxygen plasma treatment has been used by many researchers to create an effective bonding of PDMS to PDMS or glass [5,6]....
[...]
...Besides higher plasma power, an over-exposure to plasma is detrimental to the adhesiveness of PDMS to all the passivation materials, which has also been reported in previous literatures [5,6]....
[...]