Capacitive resonators and methods of fabrication

A method for fabricating micro-electro-mechanical system (MEMS) capacitive resonators, the method comprising:

• forming trenches in a semiconductor-on-insulator substrate;
• conformally coating the sidewalls of the trenches with an oxide;
• filling the coated trenches with polysilicon, wherein electrodes are derived from the polysilicon;
• forming release openings and removing the polysilicon and at least a portion of the semiconductor-on-silicon substrate without isotropic etching of the polysilicon or semiconductor portion of the semiconductor-on-silicon substrate;
• and
• removing the conformally coated oxide and an oxide of the semiconductor-on-insulator substrate, wherein a capacitive gap is formed, wherein a resonating element of one of the capacitive resonators is released.

A method for fabricating micro-electro-mechanical system (MEMS) capacitive resonators having sharply defined boundaries, the method consisting of:

• growing or depositing an oxide layer on a semiconductor-on-insulator substrate and patterning the oxide to the shape of the resonators;
• forming trenches in the semiconductor-on-insulator substrate by using the oxide layer as a mask;
• conformally coating sidewalls of the trenches with an oxide;
• filling the coated trenches with polysilicon, wherein electrodes are derived from the polysilicon;
• forming release openings and removing the polysilicon and at least a portion of the semiconductor-on-silicon substrate without isotropic etching of the polysilicon or semiconductor portion of the semiconductor-on-silicon substrate;
• and
• forming a resonating element having sharply defined boundaries of one of the capacitive resonators by removing the conformally coated oxide and an oxide of the semiconductor-on-insulator substrate, wherein a capacitive gap is formed, wherein the resonating element is released.

A method for fabricating micro-electro-mechanical system (MEMS) capacitive resonators having a height-to-width ratio of less than one, the method comprising:

• forming trenches in a semiconductor-on-insulator substrate;
• conformally coating sidewalls of the trenches with an oxide;
• filling the coated trenches with polysilicon, wherein electrodes are derived from the polysilicon;
• forming release openings and removing the polysilicon and at least a portion of the semiconductor-on-silicon substrate without isotropic etching of the polysilicon or semiconductor portion of the semiconductor-on-silicon substrate;
• and
• forming a resonating element having a height-to-width ratio of less than one of the capacitive resonators by removing the conformally coated oxide and an oxide of the semiconductor-on-insulator substrate, wherein a capacitive gap is formed, wherein the resonating element is released.