Periodic signal generators having microelectromechanical resonators therein that support surface wave and bulk acoustic wave modes of operation with different temperature coefficients of frequency
View Patent ↗A periodic signal generator is configured to generate high frequency signals characterized by relatively low temperature coefficients of frequency (TCF). This generator may include an oscillator containing a pair of equivalent MEMs resonators therein, which are configured to support bulk acoustic wave and surface wave modes of operation at different resonance frequencies. Each resonator includes a stack of layers including a semiconductor resonator body (e.g., Si-body), a piezoelectric layer (e.g., AIN layer) on the resonator body and interdigitated drive and sense electrodes on the piezoelectric layer. The oscillator is configured to support the generation of first and second periodic signals having unequal first and second frequencies (f 1 , f 2 ) from first and second resonators within the pair. These first and second periodic signals are characterized by respective first and second temperature coefficients of frequency (TCf 1 , TCf 2 ), which may differ by at least about 10 ppm/° C.
1. A periodic signal generator, comprising:
an oscillator comprising first and second equivalent microelectromechanical resonators configured to support bulk acoustic wave and surface wave modes of operation, respectively, said first and second resonators each comprising a respective stack of layers including a semiconductor resonator body, an electrically insulating mode separation layer on the resonator body, a piezoelectric layer on the mode separation layer and interdigitated drive and sense electrodes on the piezoelectric layer, said first and second equivalent microelectromechanical resonators configured to generate first and second periodic signals having unequal first and second frequencies (f 1 , f 2 ), respectively, said first and second periodic signals characterized by respective first and second temperature coefficients of frequency (TCf 1 , TCf 2 ) that differ by greater than 10 ppm/° C., where the mode separation layer comprises a material that is sufficiently thick that TCf 2 is less than about 2 ppm/° C. when the second resonator is supporting the surface wave mode of operation at the second frequency f 2 and the first resonator is concurrently supporting the bulk acoustic wave mode of operation at the first frequency f 1 ;
a frequency multiplier responsive to the first periodic signal, said frequency multiplier configured to generate a periodic output signal having a frequency equal to N times a frequency of the first periodic signal, where N is a real number greater than one; and
a mixer circuit configured to generate a periodic beat signal in response to the second periodic signal and the periodic output signal, said periodic beat signal having a frequency f b equal to |f 2 −Nf 1 | and a temperature coefficient of frequency (TCf b ) of less than a smaller of TCf 1 and TCf 2 .
2. The generator of claim 1 , wherein a pitch between each of the fingers in the interdigitated drive and sense electrodes is less than a thickness of the resonator body.
3. The generator of claim 1 , wherein:
TCf b =TCf 1 +μ f ( TCf 2 −TCf 1 ),
where μ f =f 2 /f b .
4. A periodic signal generator, comprising:
an oscillator comprising first and second equivalent microelectromechanical resonators configured to support bulk acoustic wave and surface wave modes of operation, respectively, said first and second resonators each comprising a respective stack of layers including a semiconductor resonator body, an electrically insulating mode separation layer on the resonator body, a piezoelectric layer on the mode separation layer and interdigitated drive and sense electrodes on the piezoelectric layer, said first and second equivalent microelectromechanical resonators configured to generate first and second periodic signals having unequal first and second frequencies (f 1 , f 2 ), respectively, said first and second periodic signals characterized by respective first and second temperature coefficients of frequency (TCf 1 , TCf 2 ) that differ by greater than 10 ppm/° C., where the mode separation layer comprises a material that is sufficiently thick that TCf 2 is less than TCf 1 when the second resonator is supporting the surface wave mode of operation at the second frequency f 2 and the first resonator is concurrently supporting the bulk acoustic wave mode of operation at the first frequency f 1 ;
a frequency multiplier responsive to the first periodic signal, said frequency multiplier configured to generate a periodic output signal having a frequency equal to N times a frequency of the first periodic signal, where N is a real number greater than one; and
a mixer circuit configured to generate a periodic beat signal in response to the second periodic signal and the periodic output signal, said periodic beat signal having a frequency f b equal to |f 2 −Nf 1 | and a temperature coefficient of frequency (TCf b ) of less than a smaller of TCf 1 and TCf 2 .