Provided is a dispenser for a solution including a reservoir configured to hold a suspension of micro light-emitting diodes (LEDs) suspended in a solvent; a stirrer configured to stir the suspension in the reservoir; a discharge path including a first valve configured to control outflow of the suspension from the reservoir; a filling path including a second valve configured to control inflow of the suspension into the reservoir; a hydraulic path including a third valve configured to control a pressure inside the reservoir; and a washing path connected to the first valve and configured to input a washing fluid for washing the discharge path into the discharge path, wherein the first valve includes a multi-way valve configured to selectively connect the discharge path to one of the reservoir and the washing path.

A device for picking and placing semiconductor chips includes a liquid having a first surface and a second surface and a layer of semiconductor chips disposed over the first surface. Characteristically, the first surface is a liquid-air interface. The device also includes a focused ultrasonic transducer positioned to focus acoustic wave on the layer of semiconductor chips such that a droplet including at least one semiconductor chip is ejected through the liquid-air per each actuation of the focused ultrasonic transducer through droplet ejection. The focused ultrasonic transducer includes a piezoelectric substrate having a top face and a bottom face, a Fresnel acoustic lens including a plurality of annular rings of air cavities disposed on the top face, and a first patterned circular electrode disposed over the top face and a second patterned circular electrode disposed over the bottom face. The first patterned circular electrode overlaps the second patterned circular electrode.