Micro bellow actuators

We report here a novel micromachined bellow-style actuator (microbellow) which uses a smaller real estate but is capable of larger deflections compared to a flat membrane of the same size. In this first demonstration, three-layer silicon nitride microbellows have been successfully fabricated by using polysilicon/TMAH sacrificial layer etching technology. Inside the bellows, runs of sacrificial layer are designed at the joints of every two layers to improve the boundary conditions (i.e., to reduce the stress concentration). By doing this, a 5 times improvement in burst pressure has been achieved. The large deflection of the bellow has also been demonstrated. As an example, a 800 /spl mu/m diameter circular microbellow made of 1.2 /spl mu/m thick silicon nitride can deflect more than 50 /spl mu/m in the center compared to only 13 /spl mu/m for a flat membrane of the same dimensions. Thermopneumatic actuation of the microbellow is also demonstrated.