CES 2017 was the year of always-on voice: Alexa stole the show as the speech assistant that was seemingly everywhere. The sheer variety of Alexa-enabled products was overwhelming, with everything from Hydrao’s showerhead and LG’s smart refrigerator to a cute robot from Lynx and Hubble’s moving smartcam that can follow you around the room and even act as a baby monitor all coming out with voice power. This trend creates new opportunities for manufacturers but also new challenges, especially at the voice interface level.
At the start of the audio signal chain, the tiny MEMS microphones embedded in consumer products must capture designers’ attention because it’s the microphones that directly affect customer satisfaction with voice interfaces.
“Stiction” — the word that MEMS designers utter in whispers because it strikes such fear into their hearts —-is one of the most common problems encountered with MEMS technology, microphones included. For those familiar with MEMS, stiction is scary because it has been the biggest cause of MEMS failures historically.
Stiction is a combination of the words “stick,” and “friction.” In capacitive MEMS, the relative motion of two opposing plates charged to a very high-bias voltage sense mechanical motion. If these two plates move too closely together, the strong voltage will pull them together so that the two plates are electrostatically clamped together. It can be very difficult to unstick the plates once this happens. Typically, the system needs to be powered down to release the electrostatic clamping and dissipate the charge.
Once the charge is gone, a user can mechanically release the plates by banging on or hitting the system. Even worse, each incident of stiction increases the likelihood that the plates will stick again because the anti-stiction coatings, which are only partially effective from the get-go, are damaged and degraded. Today frustrated customers who have encountered stiction are filling user forums and reddit threads with negative comments, which is not what designers want to hear after their product launches.
Stiction is catastrophic for voice interfaces and typically results in total system failure. Unfortunately, this problem is more likely to occur in many new types of IoT systems because the user is expected to tap to activate voice controls, and even a seemingly gentle touch can create stiction. Because we cannot expect users not to tap on their devices, system designers would be wise to use a new type of MEMS microphone that operates on a completely different physical principle that makes it immune to stiction.
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Piezoelectric MEM microphones, such as those that Vesper supplies, use a single plate of piezoelectric material to sense sound instead of the two or more plates that capacitive MEMS microphones use. Encountering stiction in piezoelectric microphones is as difficult as clapping with one hand or dancing a solo tango: it simply cannot occur because there is nothing to which the piezoelectric plate can stick. In addition, piezoelectric microphones are immune to dust, water, chemicals, and kitchen oils so they keep working for decades in rough conditions.
System designers of all types are putting voice interfaces into an ever-widening array of products. To delight customers, voice-enabled products must not only be beautiful and functional; they must also be reliable. Selecting the most reliable MEMS microphones on the market will help systems designers to produce voice-enabled applications that customers will love, instead of driving them to complain on user forums.
Contact Vesper to learn more about the benefits of piezoelectric MEMS microphones. Email: email@example.com
“Encountering stiction in piezoelectric microphones is as difficult as clapping with one hand or dancing a solo tango.”