Laterally-doped MEMS resonator with piezoelectric layer

A method of fabricating a semiconductor device, the method comprising:

• providing a first silicon layer, a second silicon layer and a third silicon layer, the first silicon layer being disposed between the second silicon layer and the third silicon layer;
• forming, within the first silicon layer, first and second regions, wherein forming the first and second regions comprises differently doping the first and second regions;
• forming a first microelectromechanical system (MEMS) resonant structure with the first region of the first silicon layer and forming a second MEMS resonant structure with the second region of the first silicon layer;
• disposing a piezoelectric layer over the resonant structure of the first silicon region;
• and
• disposing a conductive layer over the piezoelectric layer in a pattern that forms electrically distinct first and second electrodes;
• wherein the first MEMS resonant structure and the second MEMS resonant structure have respective first-order temperature coefficients of frequency that differ from one another due, at least in part, to the different doping of the first and second regions of the first silicon layer;
• and
• wherein the first order temperature coefficient of frequency of the resonant structure formed with the second region of the first silicon layer is at least ten times greater than the first-order temperature coefficient of frequency of the resonant MEMS member with the first region of the first silicon layer.

A method of fabricating a semiconductor device, the method comprising:

• providing a first silicon layer, a second silicon layer and a third silicon layer, the first silicon layer being disposed between the second silicon layer and the third silicon layer;
• forming, within the first silicon layer, a first region and a second region, wherein forming comprises differently doping the first region and the second region;
• forming a first microelectromechanical system (MEMS) resonant structure with the first region and forming a second MEMS resonant structure with the second region, wherein the forming of the first region and the second region, the forming of the first MEMS resonant structure and the forming of the second MEMS resonant structure are performed in a manner such that a first-order temperature coefficient of frequency (TCF) of the second MEMS resonant structure is at least ten times greater than the first-order temperature coefficient of frequency of the first MEMS resonant structure;
• disposing a piezoelectric layer over the first region;
• and
• disposing a conductive layer over the piezoelectric layer in a pattern that forms electrically distinct first and second electrodes;
• wherein differently doping comprises
• forming one or more trenches in the first silicon layer in a manner abutting the first region,
• depositing a dopant source into the one or more trenches as well as onto a surface of the first region,
• performing a thermally-anneal process to drive dopant from the dopant source into a top surface of the first region as well as into at least one lateral side of the first region, the at least one lateral side being defined by the one or more trenches.