Substrate for diaphragm-type resonant mems devices, diaphragm-type resonant mems device and method for manufacturing same

A method for producing a di pe resonant micro electro mechanical system device, the method comprising the steps of:

• forming an upper electrode on the piezoelectric film side of a substrate for diaphragm-type resonant micro electro mechanical system devices in which a first silicon oxide film formed by thermal oxidation or by a process including a heat treatment at 900° C. or above, a second silicon oxide film having a stress with an absolute value of 100 MPa or less, a lower electrode, and a piezoelectric film are laminated in this order on a first surface of a silicon substrate;
• and
• etching the opposite side surface of the first surface of the silicon substrate by deep reactive ion etching until the first silicon oxide film is exposed so as to form a recess, and thereby forming a diaphragm structure including a diaphragm having the first silicon oxide film and the second silicon oxide film,
• wherein when the film thickness of the first silicon oxide film is designated as t1, the film thickness of the second silicon oxide film is designated as t2, and the proportion of the film thickness of the second silicon oxide film with respect to the sum of the film thickness of the first silicon oxide film and the film thickness of the second silicon oxide film, t2/(t1+t2), is designated as R2, the following conditions are satisfied:
• 0.10 μm≦t1≦2.00 μm;
• and
• R2≧0.70.

A diaphragm-type resonant micro electro mechanical system device comprising:

• a laminate in which a first silicon oxide film, a second silicon oxide film, a lower electrode, a piezoelectric film, and an upper electrode are laminated in this order;
• and
• a silicon substrate that supports the laminate through the first silicon oxide film side of the laminate,
• wherein the second silicon oxide film having a stress with an absolute value of 100 MPa or less, and
• when the film thickness of the first silicon oxide film is designated as t1, the film thickness of the second silicon oxide film is designated as t2, and the proportion of the second silicon oxide film with respect to the sum of the film thickness of the first silicon oxide film and the film thickness of the second silicon oxide film, t2/(t1+t2), is designated as R2, the following conditions are satisfied:
• 0.10 μm≦t1≦2.00 μm;
• and
• R2≧0.70.

A substrate for diaphragm-type resonant micro electro mechanical system devices, the substrate comprising:

• a first silicon oxide film formed by thermal oxidation or by a process including a heat treatment at 900° C. or above;
• a second silicon oxide film having a stress with an absolute value of 100 MPa or less;
• a lower electrode;
• and
• a piezoel ectric film
• laminated in this order on a surface of a silicon substrate,
• wherein when the film thickness of the first silicon oxide film is designated as t1, the film thickness of the second silicon oxide film is designated as t2, and the proportion of the second silicon oxide film with respect to the sum of the film thickness of the first silicon oxide film and the film thickness of the second silicon oxide film, t2/(t1+t2), is designated as R2, the following conditions are satisfied:
• 0.10 μm≦t1≦2.00 μm;
• and
• R2≧0.70.