Continual downsizing of technology means that researchers have to develop ever more ingenious methods of packaging and protecting their tiny devices. Jae-Wung Lee and co-workers at the A*STAR Institute of Microelectronics, Singapore, are at the forefront of efforts to develop safe but functional encasements for microelectromechanical systems (MEMS), such as sensors, switches or radio filters.
An optical image of a 400-by-400-micrometer, thin-film MEMS encapsulation developed using the new double-layer capping technique. The smaller square caps sit on top of holes, allowing access to the cavity below while protecting the devices within.
Reproduced from Ref. 1 © 2013 IOP Publishing
“MEMS devices need certain ambient conditions to operate properly and have fragile hanging structures that must be protected,” says Lee. “We developed a new thin-film encapsulation (TFE) technique to meet these two requirements.”
During TFE, a MEMS device is embedded in a ‘sacrificial layer’ of one material before adding a ‘cap layer’ of another type of material. By leaving some access channels in the cap layer, researchers can pipe in a chemical that reacts with and removes the sacrificial layer, leaving the MEMS device in a cavity protected by the cap layer.
Compared with other encasement methods, TFE can be performed cheaply using the same techniques that are used to build MEMS devices, and it produces less bulky packaging. However, previous attempts at TFE have suffered from two problems: depending on the design of the access holes in the cap layer, removing the sacrificial layer can be time consuming, and mass loading can damage moving components, such as resonators, in MEMS devices.
“Solving both these issues simultaneously is difficult because one can become severe when the other is solved,” says Lee. “We proposed fabricating the cap layer on two levels.”
The team’s design involves making a grid of square holes in the lower cap layer. A secondary square layer with four legs is deposited on top of each hole, leaving sideways access gaps underneath, rather like a chimney cap. These caps allow access for removing the sacrificial layer while protecting the device beneath from mass loading.
The researchers tested their idea using silicon oxide as the sacrificial layer and aluminum nitride for the cap layers. They were able to remove the silicon oxide using an acid vapor in just 20 minutes, compared to 8 hours for previous designs. The result was a strong, free-standing cap with a 3-micrometer-thick cavity underneath.
Lee and co-workers state that their TFE cavity design could be built using other materials and may find application beyond MEMS, for instance in microbiology. “Electrodes embedded in a TFE cavity could be used to apply electrostatic forces to biomolecules or even act as a microheater,” says Le
The A*STAR-affiliated researchers contributing to this research are from the Institute of Microelectronics.
Lee, J.-W., Sharma, J., Singh, N. and Kwong, D.-L. Development and evaluation of a two-level functional structure for the thin film encapsulation. Journal of Micromechanics and Microengineering 23, 075013 (2013).
Fraunhofer ISE Pushes World Record for Multicrystalline Silicon Solar Cells to 22.3 Percent
25.09.2017 | Fraunhofer-Institut für Solare Energiesysteme ISE
Producing electricity during flight
20.09.2017 | Albert-Ludwigs-Universität Freiburg im Breisgau
Controlling electronic current is essential to modern electronics, as data and signals are transferred by streams of electrons which are controlled at high speed. Demands on transmission speeds are also increasing as technology develops. Scientists from the Chair of Laser Physics and the Chair of Applied Physics at Friedrich-Alexander-Universität Erlangen-Nürnberg (FAU) have succeeded in switching on a current with a desired direction in graphene using a single laser pulse within a femtosecond ¬¬ – a femtosecond corresponds to the millionth part of a billionth of a second. This is more than a thousand times faster compared to the most efficient transistors today.
Graphene is up to the job
At the productronica trade fair in Munich this November, the Fraunhofer Institute for Laser Technology ILT will be presenting Laser-Based Tape-Automated Bonding, LaserTAB for short. The experts from Aachen will be demonstrating how new battery cells and power electronics can be micro-welded more efficiently and precisely than ever before thanks to new optics and robot support.
Fraunhofer ILT from Aachen relies on a clever combination of robotics and a laser scanner with new optics as well as process monitoring, which it has developed...
Plants and algae use the enzyme Rubisco to fix carbon dioxide, removing it from the atmosphere and converting it into biomass. Algae have figured out a way to increase the efficiency of carbon fixation. They gather most of their Rubisco into a ball-shaped microcompartment called the pyrenoid, which they flood with a high local concentration of carbon dioxide. A team of scientists at Princeton University, the Carnegie Institution for Science, Stanford University and the Max Plank Institute of Biochemistry have unravelled the mysteries of how the pyrenoid is assembled. These insights can help to engineer crops that remove more carbon dioxide from the atmosphere while producing more food.
A warming planet
Our brains house extremely complex neuronal circuits, whose detailed structures are still largely unknown. This is especially true for the so-called cerebral cortex of mammals, where among other things vision, thoughts or spatial orientation are being computed. Here the rules by which nerve cells are connected to each other are only partly understood. A team of scientists around Moritz Helmstaedter at the Frankfiurt Max Planck Institute for Brain Research and Helene Schmidt (Humboldt University in Berlin) have now discovered a surprisingly precise nerve cell connectivity pattern in the part of the cerebral cortex that is responsible for orienting the individual animal or human in space.
The researchers report online in Nature (Schmidt et al., 2017. Axonal synapse sorting in medial entorhinal cortex, DOI: 10.1038/nature24005) that synapses in...
Whispering gallery mode (WGM) resonators are used to make tiny micro-lasers, sensors, switches, routers and other devices. These tiny structures rely on a...
19.09.2017 | Event News
12.09.2017 | Event News
06.09.2017 | Event News
25.09.2017 | Power and Electrical Engineering
25.09.2017 | Health and Medicine
25.09.2017 | Physics and Astronomy