In this article, dive deeper into understanding the different latest technologies behind different MEMS devices and applications, including RF MEMS, MEMS loudspeakers, BioMEMS and PowerMEMS. Learn about what they are, their objectives and most importantly how they will transform the way that existing technologies are used!
Note: This article is a continuation of our previous article, Introduction to Microelectromechanical Systems (MEMS).
Recap: What are MEMS?
MEMS, or MicroElectroMechanical Systems in full, are a class of systems that combine electronic, electrical, and mechanical components into a single, integrated device.
Uniquely, MEMS are characterised by their ultra compact physical size (one millimeter down to one micron!) and microfabrication process. Microfabrication is the same process that’s being used to manufacture semiconductor-based components like the integrated circuits in our CPUs – It’s for this reason that MEMS have been easily and heavily assimilated into embedded applications like our mobile phones & wearable devices.
MEMS are not new to our modern technologies. Over the past three decades, MEMS research has yielded commercial applications in sensing temperature, pressure, inertial forces, etc. In spite of this, research and development in MEMS remains very active over the years. In particular, a large focus has been placed on integrating a greater variety of components and experimenting with different microfabrication processes to meet various operational demands.
Radio Frequency MEMS
Radio Frequency MEMS, or RF MEMS for short, are MEMS that have incorporated RF-based passive components for radio communication.
These components refer to our typical resistors, capacitors, inductors, etc. that are used in RF circuits. However, because passive components in RF applications have to sustain performance at high signal frequencies, they face unique design requirements and challenges. If you are keen to know more about RF circuits, click here.
In general, RF MEMS have improved signal isolation in addition to achieving low power dissipation, reduced cost, size, and weight. Some of the broad applications of RF MEMS are shown in the graphic below:
RF MEMS Switches
Among RF MEMS applications, switches have gained the most development traction, with recent breakthroughs in commercial offerings.
The new RF MEMS switches developed by MenloMicro contain a conductive beam actuator made of a proprietary alloy. The alloy is pulled towards the electrical contact by a high-voltage static electric field to close the switch.
These switches approach the performance of an “ideal switch”, featuring super low resistance in the “on” state, but super high resistance when “off”. In addition, they feature high linearity, low switch time and low power consumption, as well as the conventional robustness and reliability of MEMS-based design.
Cutting edge RF MEMS switches are now being used in aerospace, military, and wireless-infrastructure industries to deliver high quality communication at massive rates. Nonetheless, we expect that the applications for these RF MEMS devices will continue to evolve over time as new technologies and research findings begin to unfold.
While MEMS technology has been around for the past three decades for microphones and accelerometers, MEMS loudspeakers have only recently become an significant field of MEMS development.
In general, MEMS speakers work by using thin piezoelectric films that deform when a voltage is applied across it. This mechanical deflection then causes a displacement in the surrounding air to generate sound waves.
MEMS loudspeakers have two primary advantages: size and power efficiency. They can be seamlessly integrated into the PCB as a single module, simplifying product design and saving space. In addition, the high intrinsic impedance of MEMS speakers requires a lower driving current and thus consumes less power.
MEMS Speakers in Earbuds
Their two benefits have led to MEMS loudspeakers being popular for occluded-ear (or in-ear) applications, such as wireless earbuds. The small form factor allows the use of larger batteries, which coupled with the improved battery consumption results in significantly improved battery life for a better user experience.
New Designs Enabled by MEMS Speakers
Due to their small size, MEMS loudspeakers typically comprise an array of MEMS speakers. This is comparable to how individual LEDs are of insufficient brightness, and are typically used in arrays to achieve desired lighting.
The results are some very interesting and compact designs, such as USound’s Proteus 2.0 shown below. The base box contains a regular subwoofer, while each of the differently oriented three tubes contain 20 MEMS speakers each to achieve 360 degree sound output.
These arrays are also lightweight and thin options to replace full-sized speakers where space and weight are critical design considerations. For example, reducing the weight of vehicles by mounting the MEMS speaker array on the car ceiling.
If you are interested in the specific technologies used by the key players in the MEMS loudspeaker market, this article by Mike Klasco provides a detailed description.
BioMEMS, short for Biomedical or Biological MEMS, is a subset of MEMS for biological applications. There are two primary types of BioMEMS, one involving biological procedures (eg. drug delivery), and another that utilises biological molecules for their operation (eg. virus detection).
There are a broad number of applications of BioMEMS used today. For example, the glucose sensor below uses a micro transducer of about 1mm long by 200 µm wide to sense blood glucose levels! When a drop of blood is placed onto the transducer, the coating on the transducer begins a glucose oxidation reaction with the glucose in the blood plasma. The electrons produced by this reaction becomes a current that is measured by the device and converted to a glucose level reading.
BioMEMS also overlaps heavily with two other active fields of development, Lab-on-Chip (LOC) and Micro Total Analysis Systems (µTAS). LOCs are devices that integrate laboratory functions onto an integrated circuit, handling volumes of sub pico-litres. On the other hand, µTAS is a type of LOC that performs an automated and complete chemical analysis of a given sample – shrinking an entire series laboratory procedures into mere micrometers in form factor!
These technologies are targeted at developing Point-Of-Care (POC) Devices. Robust yet tiny diagnostic devices featuring BioMEMS technology could bring portable and effective testing to less developed countries where laboratory-scale tools are not available.
3D Printing: BioMEMS Molds for COVID-19 Testing at UC Berkeley
Researchers from UC Berkeley utilised projection micro-stereolithography to produce molds for multiplex microfluidic devices that can be used in the fight against COVID-19. These POC devices are equipped with a sensor and can be used to perform a traditional antibody test for patients who are infected.
Microfluidic multiplex devices allow for a single chip to carry out multiple tests. For instance, some channels can carry antibodies while others are allocated for detecting viral RNA. With LOC technology, large-scale testing for COVID 19 can be achieved with automation and high-throughput screening. Read more about their work here.
BioMEMS is a very diverse field of research that continues to evolve. If you would like to learn more about BioMEMS, I strongly encourage you to visit this 30-minute learning module by the Southwest Center for Microsystems Education.
The last type of MEMS that we will look at are PowerMEMS. PowerMEMS aims to develop technology for replacing rechargeable batteries in a wide range of applications through energy generation or conversion. There are two main types of PowerMEMS projects, Scavenger Systems and Fuel-based Systems.
Scavenger System PowerMEMS
Many electronics that are available today are now power efficient enough to operate on minute amounts of energy that can be ‘scavenged’ from the environment. The scavenger system’s class of PowerMEMS aims to convert environmental energy such as thermal or kinetic energy through a dedicated microsystem.
One way through which this is achieved is by using resonant spring-mass systems enclosed in a frame that oscillate in response to external vibrations. The mechanical energy from the oscillation is harvested into electrical energy. In the figure below, the converter is represented by a damper on the spring-mass system. In reality, the converter may be implemented with an electromagnet or piezoelectric materials.
You can read more about Scavenger System PowerMEMS here.
Fuel-based PowerMEMS aim to miniaturise generators and turbines that are commonly found in power plants. This would allow portable devices to take advantage of the energy density of most fuels, which vastly exceed those of today’s best performing batteries. Just imagine – what if we had a mini power plant in our pockets?
You can read more about Fuel-based PowerMEMSi, their unique design considerations and challenges here.
Summary & Conclusion
We kicked off this article by looking at some breakthroughs in MEMS technology, such as RF MEMS switches and RF loudspeakers. Then, we talked about some areas of modern research, like BioMEMS and PowerMEMS. All of these are important areas of study and we hope that you enjoyed learning about them!
If you would like to read deeper reading on different MEMS, here are the summarised links of the resources that we’ve mentioned.
- How RF MEMS Tech Finally Delivered the “Ideal Switch”
- The Impact of MEMS Speakers in Audio
- BioMEMS Overview
- PowerMEMS Project Homepage
Be sure to also check out our previous articles on MEMS technologies!