Wafers for MEMS Based Acoustic Resonators

Silicon Microstructure for MEMS Sensors

Piezoelectric MEMS / AE sensors consist of resonant silicon microstructure with a thin piezoelectric layer mounted on a ceramic housing. Due to the development of thin piezoelectronic layers and the deposition of substrates, piezoelectric MEMS sensors can be designed to detect and operate. The most important material and geometric characteristics for scanning are the piezoelectric coefficient, the electromechanical coupling coefficient and the mechanical quality factors (resonance frequency, residual voltage, etc.) 

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What is a MEMS Based Acoustic Resonators

To understand how MEMS based acoustic resonators work, we first have to understand what they are made of. These wafer based devices consist of a solid piece of metal such as solid steel or tin and a layer of thin sheets of wafer material called a wafer top. The wafer top is constructed from a number of different alloys, which include the most commonly used, silicon. Silicon is the most commonly used material because it's inexpensive, conductive of electricity and has excellent electrical and mechanical properties.

Researchers have purchased the following Silicon Wafer/Oxide Item to research and development of fabrications methods.

Item #3330
50.8mm P/B <100> 1-10 ohm-cm 270um SSP Prime Grade with 300nm of Thermal Oxide

When silicon is used as a wafer, it's wrapped by a layer of an electrically conductive metal such as copper. The copper layer serves to keep the wafer from being negatively charged, which can be harmful to its component parts. This layer of metal also insulates the wafer from sound, which makes for a very sturdy device. The thickness of the wafer material makes this device ideal for use in a variety of situations including bulletproof vests, protective coatings on fire trucks and police cars, and in a variety of other industries.

Since the wafer top acts like a barrier between the wafer and the rest of the device, acoustic transducers are built into the device. These transducers are able to detect the thickness of the wafer. If the wafer is too thick, the transducers will not detect them and the resonator will not function. On the other hand, if the wafer is too thin, the resonator will absorb too much energy and break. Therefore, wafer thickness is important but not nearly as important as the other factors that determine the performance of a MEMS based acoustic transducer.

A second factor that affects the performance of the resonators is the thermal conductivity of the metal being used to make the wafer. Metals that have higher thermal conductivity include aluminum and titanium. Usually thicker metal like these two metals will provide more room for the wafer to develop micro-spheres. Microspheres are areas of unperceived heat, similar to what you feel when you touch an aluminum foil. When the temperature rises, this heat dissipates into the room and you will not feel it.

The thickness of the wafer also affects the amount of power needed to produce the desired frequencies. If the wafer is too thick, then it reduces the amount of power that can be utilized to resonate the wafer. Because the wafer is too thick, there is less room for the waves to resonate. The thicker metal will also make it harder for the waves to travel through the material without breaking or sliding. The reduction in the amount of power that can be utilized to resonate a thin wafer will reduce the power necessary to create the audio frequency.

Most industries use flat or thick metallic wafers in many types of applications. These include MEMS enabled thin film displays and computer chips. If you are looking at creating your own wafer based instruments, you will have to take into consideration the differences in the thickness of the metallic wafers as well as the metal that is used to make them. Because thin metals can conduct the electrical current, you must take into consideration the thickness of the wafer and the metal that it is made from. Typically if you are working with a thin sheet metal, then you do not need as thick a wafer and the same would apply if you were working with a thick wafer.

The application of MEMS based acoustic resonators is very common in the medical industry. One example would be a neck pain device that is worn on a patient's head to help with relief of pain. You may also find these devices used in the military to help train new soldiers in basic combat skills. Since the wafers are so thin, the acoustic vibrations created by the device can be heard as the soldiers move around and train.

Another example of where these products can be used would be for a fan blade on a jet engine. Again, since the wafers are thin, the air flow through the blades can be increased. Because the air is expanded, you will find that there are more wind resistance and hence more power is produced. This is just one application of MEMS based thin metal wafer tools. Since they are quite inexpensive in comparison to other tools, you can easily incorporate them into your overall toolbox without having to spend a lot of money.