Its very new apparently. It would seem that these types of drivers will mostly be used for tweeters and can be used in headphones as well. Very interesting development
https://www.digikey.co.za/en/articles/techzone/2019/oct/what-are-the-advantages-of-mems-loudspeakers?utm_medium=email&utm_source=tnl&utm_campaign=60661_TNL1912A&utm_content=article2title_ZA&utm_cid=10648111&mkt_tok=eyJpIjoiT0dFMU9EZGpZamc1TW1FMCIsInQiOiJHMFYzUVh2VEF1ZG03TFcwTmhFKzZFTVN5OVF5XC90WW9YdGdpbUFZb0R2RlpldFIxVkVrakV0dzFrdmErUmUxc1k5R2p1cHpQUkNCVjNsajZFTTFVb3hnMm1Wbk41TGdsSjZoVXE2enVNaDIxRGxyT0U4MEs0ZXhYYlZ1RnJCOUgifQ%3D%3D
https://www.digikey.co.za/en/articles/techzone/2019/oct/what-are-the-advantages-of-mems-loudspeakers?utm_medium=email&utm_source=tnl&utm_campaign=60661_TNL1912A&utm_content=article2title_ZA&utm_cid=10648111&mkt_tok=eyJpIjoiT0dFMU9EZGpZamc1TW1FMCIsInQiOiJHMFYzUVh2VEF1ZG03TFcwTmhFKzZFTVN5OVF5XC90WW9YdGdpbUFZb0R2RlpldFIxVkVrakV0dzFrdmErUmUxc1k5R2p1cHpQUkNCVjNsajZFTTFVb3hnMm1Wbk41TGdsSjZoVXE2enVNaDIxRGxyT0U4MEs0ZXhYYlZ1RnJCOUgifQ%3D%3D