Laboratory of Advanced Microfluidic Systems

Our past efforts on promotion the education on microelectromechanical systems (MEMS) are listed below. Here, we would like to sincerely acknowledge the support from the Office of Education Development and Gateway Education via a Teaching Development Grant for both the laboratory module development and facilitating students' term projects as shown below.  
Laboratory 1: Basic Photolithography  

Objective: This lab session is to gain the basic understanding and experience for the photolithography, including standard cleaning, photoresist spin coating, and UV exposure.

Background: Photolithography is the fundamental process in semiconductor industry and microelectromechanical systems (MEMS). In contrast to the traditional machining process, UV light is used to transfer a pattern from a photo mask to the photosensitive material, photoresist. After UV exposure, positive photoresist becomes dissolvable in the developer, while the negative photoresist is the opposite. To ensure the quality, a series of chemical rinsing should be first conducted to remove the dust and organic/inorganic contamination. After cleaning, the photoresist is applied to the substrate using spin coating. The liquid solution of photoresist is dispensed onto the substrate, followed by spinning the substrate rapidly to achieve a uniform photoresist layer. Next, the substrate is soft-baked on a hotplate to remove the excess solvent within the photoresist. At last, with the assistance of UV aligner, the substrate with coated photoresist is exposed to a pattern of UV light defined by a photo mask.


Laboratory 2: Fabrication of Microelectrodes  

Objective: This lab session is to gain the basic understanding and experience for fabricating micro structures, including standard photolithography and wet etching.

Background: Indium tin oxide (ITO) can be coated on glass slide to form a conductive layer with a very small resistance. With a standard wet etching method, we can fabricate electrodes with this layer. Bonded with PDMS layer which has microfluidic structures, the glass slide can be used for biological applications, such as cell counting and trapping. To get the micro patterns of electrodes, we coat a protective layer of photoresist on the ITO-coated side of glass slide at first. After using method of photolithography, the structures of electrodes can be achieved and they can prevent required ITO from being etched. After etching ITO and removing all the photoresist, the required micro-electrodes can be obtained on ITO coated glass slide.


Laboratory 3: Molding of Polydimethylsiloxane (PDMS)  

Objective: This lab session is to gain the basic understanding and experience for PDMS molding, including preparation of PDMS pre-polymer, degassing, and molding. Students will learn how to fabricate the PDMS-based microstructure.

Background: Within the last decade, the use of microfluidic devices, ranging from single etched channel structures in glass substrates to complex multilayer fluidic networks, for the manipulation of biomolecules has grown exponentially. The popularity of this field can be attributed to its interdisciplinary nature. From a biological perspective, recent advances in genomics and proteomics have generated a need for cheaper high-throughput screening (HTS) platforms. However, the successful design of such platforms requires some knowledge in a variety of disciplines, ranging from engineering (design and manufacture of the microfluidic device) to materials science (selecting the appropriate substrate for device fabrication) to fluid mechanics for the optimization of the flow and/or mixing conditions. With more microfluidic platforms being developed as collaborative projects between laboratories as well as through industrial partnerships, devices with highly advanced functionalities are being produced for applications such as protein crystallization and tissue engineering that incorporates blood vessels.

Currently, a silicone rubber known as polydimethylsiloxane (PDMS) is probably the most popular material for rapid prototyping of microfluidic devices in research laboratories due to its ease of use in the laboratory, low cost, and properties that are suitable for a wide range of applications. In contrast, hard polymers are usually preferred for commercial device development due to their robustness and amenability for large scale manufacture by processes such as hot embossing and injection molding.


Project Guidelines on MEMS Design  

Objectives: The aim of this MEMS project is to provide an opportunity for MBE3115 students to experience a more comprehensive thinking of conceptual design, device design, fabrication, modeling and simulation, based on the techniques learnt from this course. Further we would be excited to see any novel ideas in the proposals, too.

Project Style: Individual project


Preparation (BONUS 2 % of the course)
1. Choose a published/existing MEMS device searchable on the Internet, or you may propose a new MEMS device based on your interest.
2. Please confirm with the lecturer about the device you want to work with in this project. The lecture will take records of your chosen device so that you will have this part of the marks. Your device should not be identical with any other students in this course. If possible, please stick with the fabrication processes compatible in our department.

MEMS Design Report (4 pages, 15 % of the course)
3. Submit the softcopy of design report via the course webpage. The report should be no more than 4 pages (please use the provided report template with font style ‘Garamond’, size 11, and single-line spacing). In the report, you have to mention a list of references. You should describe the chosen MEMS device in terms of its: 1) target application (3 %), 2) device geometry (1.5 %) and working principle (1.5 %), and 3) feasible fabrication process (9 %) based on the techniques you learnt in this course. You may take answers of the past problem sets (e.g. Pset 1 Q3 and Pset 2 Q2) as reference. If there are any new techniques, please describe the basic principles of the techniques in the report as well.

Project Feedback
4. Feedback will be given by Ray. Meetings maybe called by Ray to improve the fabrication feasibility.

MEMS Design and Modeling Report (4 + 4 pages, 15 % of the course)
5. Submit the softcopy of the final report via the course webpage.
a. The first part of this report should be the MEMS Design Report (4 pages max), including corrections of the fabrication process if there is any. NOTE that any improvement of this part will induce marks added back to your previously submitted Design Report (i.e. the previous 9 % for the fabrication process).
b. The second part (4 pages max) is weighed 15 % of the course. It should include the model (i.e. from the basic governing equations to the transfer function) describing functions of the selected MEMS device, and any basic analyses based on what you have learnt in other MBE courses, or on the web. Please also mention the related course/materials and explain how they are related to your analyses.

After the semester
6. We will select the outstanding proposals and ask for meetings with you after the semester. We will decide whether we can fabricate and implement the MEMS development. We will invite selected candidates to develop their products. Depending on the nature of work/my financial situation, we may support the selected students under the CIS/CWS scheme.
7. Upon completion of the product development, we will look into possibilities for any competitions, academic achievements, or patent applications. Hope in this way, the process can help students to develop the overall sense of MEMS device research and development (R&D).
8. If you wish to, this may become your FYP in the next year under the supervision of Ray.

Equipment Available in MBE
1. UV aligner
2. Spin-coater
3. Oxygen/air plasma bonding
4. Sputtering deposition machine (copper/aluminum/chromium/gold)
5. Reactive ion etch machine
6. Wet etching facilities

Let’s enjoy MEMS!



Laboratory of Advanced Microfluidic Systems | Department of Mechanical and Biomedical Engineering | City University of Hong Kong
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