Acoustically actuated flextensional SixNy and single-crystal silicon 2-D micromachined ejector arrays

We propose using two-dimensional (2-D) micromachined droplet ejector arrays for environmentally benign deposition of photoresist and other spin-on materials, such as low-k and high-k dielectrics used in IC manufacturing. Direct deposition of these chemicals will reduce waste as well as production cost. The proposed device does not harm heat or pressure sensitive fluids and they are chemically compatible with the materials used in IC manufacturing. Each element of the 2-D ejector array consists of a flexurally vibrating circular membrane on one face of a cylindrical fluid reservoir. The membrane has an orifice at the center. A piezoelectric transducer generating ultrasonic waves, located at the open face of the reservoir, actuates the membranes. As a result of this actuation, droplets are fired through the membrane orifice. Ejector arrays were built with either Si_xN_y or single-crystal silicon membranes using two different fabrication processes. We show that single-crystal silicon membranes are more uniform in their thickness and material quality than those of Si_xN_y membranes. The single-crystal silicon membrane-based devices showed thickness and material uniformity across all the membranes of an array. This improvement eliminated nonuniform membrane resonance frequencies across an array as observed with Si_xN_y membrane-based devices. Therefore, it should be possible to repeatably build devices and to predict their dynamic characteristics. Using the fabricated devices, we demonstrated water ejection at 470 kHz, 1.24 MHz, and 2.26 MHz. The corresponding droplet diameters were 6.5, 5, and 3.5 μm, respectively.