Crystal oscillator and method of making the same

A method of making a crystal oscillator, comprising the steps of:

• (a) forming a bottom electrode layer on a lower surface of a piezoelectric substrate, the bottom electrode layer having a bottom work portion spaced apart from a plurality of edges of the lower surface of the piezoelectric substrate, and a bottom extension extending from the bottom work portion toward one edge of the lower surface of the piezoelectric substrate;
• (b) adhering a temporary substrate to the lower surface of the piezoelectric substrate so as to cover the bottom electrode layer;
• (c) patterning an upper surface of the piezoelectric substrate that is opposite to the lower surface thereof so that the piezoelectric substrate is formed with a thinned portion and two side portions located on two opposite ends of the thinned portion, the thinned portion having the lower surface of the piezoelectric substrate and an upper surface opposite to the lower surface, the upper surface and the lower surface respectively defining an upper surface work portion and a lower surface work portion spaced apart from a plurality of ends of the thinned portion, the lower surface work portion being formed with the bottom work portion of the bottom electrode layer, at least one of the two side portions having a recessed portion extending inwardly from a top surface thereof, wherein the upper surface of the thinned portion and a bottom surface of the recessed portion are flush with each other;
• (d) forming a top electrode layer on the upper surface of the thinned portion, the top electrode layer having a top work portion located on the upper surface work portion, and a top extension extending from the top work portion onto the bottom surface of the recessed portion;
• and
• (e) removing the temporary substrate from the lower surface of the piezoelectric substrate to expose the bottom electrode layer.