Challenges and opportunities in MEMS development, assembly and applications

Citation

Hsieh, S.-J.(T). (2013), "Challenges and opportunities in MEMS development, assembly and applications", Assembly Automation, Vol. 33 No. 2. https://doi.org/10.1108/aa.2013.03333baa.001

Challenges and opportunities in MEMS development, assembly and applications

Article Type: Viewpoint From: Assembly Automation, Volume 33, Issue 2

Micro-Electro-Mechanical Systems (MEMS) are miniaturized mechanical and electro-mechanical devices and structures that are made using micro-fabrication techniques. The physical dimensions of MEMS devices can range from below 1 μm to several millimeters. The types of MEMS devices vary from relatively simple structures having no moving elements, to complex electromechanical systems with multiple moving elements under the control of integrated microelectronics. MEMS assembly involves joining two or more components to form a MEMS device.

A basic requirement of automated micro-assembly is that the system must be able to transport micro-scale parts and components and to manipulate them so that precise spatial relations (with micro-scale tolerances) can be established. For example, in die alignment and parts insertion or in packaging processes such as die bonding, device sealing, etc. the operating tolerances are very small and therefore, assembly and positioning tasks require very high precision and repeatability. In addition, assembly techniques for the macro domain do not directly translate to the micro-domain because of the dominance of effects such as Van der Waals forces, surface tension, and electrostatic forces. Current assembly technologies include:

1. 1.

   Robotic assembly. extends conventional “pick and place” assembly into the micro-domain. Micro-parts are fed by a feeding device, picked up by a tool such as a micro-gripper, and then moved to a desired position. The parts are then positioned at a target site using various releasing techniques. Many manipulator devices have been developed, such as a six degrees-of-freedom (DOF) parallel micro-manipulator developed by the Agency of Industrial Science and Technology (AIST) in Japan. In addition, many commercial positioning systems have been applied for robotic micro-handling. These are usually composed of precision mechanical rails and actuators based on direct-current (DC) motors, piezoelectric actuators, and piezoelectric motors. Many micro-gripper designs and releasing strategies have also been developed, including vacuum gripper, electrostatic gripper, capillary gripper, van der Waals gripper, vibration release, and snap-locking fixing.Robotic micro-assembly has limitations, including:

2. 2.

   depth of view and the contradiction between resolution and field of view of optical microscopes;

3. 3.

   difficulties in implementing force control due to performance of the sensors; and

4. 4.

   limited space for micro-grippers.

5. 5.

   Self-assembly. In self-assembly, micro-parts are fed to the assembly process. They are then driven toward the receptor sites using various agitation methods and finally positioned and aligned using the principle of minimum potential energy. The receptor sites can be micro-machined cavities or electrostatic traps; short-range attractive forces and random agitation of the parts serve to fill the sites.

Today, the principles of fluidic agitation, vibration excitation, and pattern matching have become widely accepted concepts in self-assembly of micro-parts. However, reliable and reproducible 3D self-assembly of micro-parts is still an open problem. Another challenge to be solved in all self-assembly is that the micro-parts might not go to the desired position due to friction and intermediate energy states.

MEMS future applications

In launching Central Nervous System for the Earth (CeNSE), Hewlett-Packard estimated that about 1 trillion nano sensors and actuators will be deployed for applications such as climate monitoring, oil exploration and production, assets and supply chain tracking, smart highway infrastructure, tsunami and earthquake warning, smart grids and homes, and structural health monitoring. Growth could be significantly accelerated if MEMS R&D speed could be increased to 15 cycles/year, and standardized MEMS processes become available for the fastest growing products. However, this would require significant funding exceeding capability of any single company. Areas for future research include:

• •

  Assembly of complex multi-functional MEMS sensors. For example, pill cameras are an application of MEMS that allow physicians to capture images inside the body. A possible enhancement would be for this device to also include an actuator to plow away blockages and another actuator to remove excess tissue.

• •

  Development of complex infrared MEMS sensors. An infrared detector and image array embedded within a smartphone could be used for quick screening of various parts of the body. For example, infrared imaging has been applied for breast cancer screening, skin cancer detection, and early detection of diabetes.

Sheng-Jen (“Tony”) HsiehBased at the Rockwell Automation Laboratory, Texas A&M University, Texas, USA