MEMS-based, computer systems, clock generation and oscillator circuits and LC-tank apparatus for use therein

• US 20030210101A1
• Filed: 02/26/2003
• Published: 11/13/2003
• Est. Priority Date: 02/26/2002
• Status: Active Grant

• Current Assignee: Board of Regents of the University of Michigan (University of Michigan)
• Original Assignee: Board of Regents of the University of Michigan (University of Michigan)
• Inventors: Brown, Richard B., McCorquodale, Michael S.
• Granted Patent: US 6,972,635 B2
• Time in Patent Office: Days
• US Class Current: 331/117FE
• CPC Class Codes: H01F 17/0006 Printed inductances printed coils for dynamo-electric machines H02K3/26; printed circuits H05K
• CPC Class Codes: H01G 5/40 Structural combinations of variable capacitors with other electric elements not covered by this subclass, the structure mainly consisting of a capacitor, e.g. RC combinations
• CPC Class Codes: H01L 23/5227 Inductive arrangements or effects of, or between, wiring layers other inductive arrangements H01L23/645
• CPC Class Codes: H01L 2924/00 Indexing scheme for arrangements or methods for connecting or disconnecting semiconductor or solid-state bodies as covered by H01L24/00
• CPC Class Codes: H01L 2924/0002 Not covered by any one of groups H01L24/00, H01L24/00 and H01L2224/00
• CPC Class Codes: H01L 2924/3011 Impedance
• CPC Class Codes: H03B 5/1212 the amplifier comprising a pair of transistors, wherein an output terminal of each being connected to an input terminal of the other, e.g. a cross coupled pair
• CPC Class Codes: H03B 5/1228 the amplifier comprising one or more field effect transistors
• CPC Class Codes: H03B 5/124 the means comprising a voltage dependent capacitance
• CPC Class Codes: H03B 5/18 with frequency-determining element comprising distributed inductance and capacitance
• CPC Class Codes: H03B 5/32 being a piezoelectric resonator selection of piezoelectric material H10N30/00
• CPC Class Codes: H03H 2007/006 MEMS
• CPC Class Codes: H03H 7/0115 comprising only inductors and capacitors H03H7/075, H03H7/09, H03H7/12, H03H7/13 take precedence

Abstract

MEMS-based, computer system, clock generation and oscillator circuits and LC-tank apparatus for use therein are provided and which are fabricated using a CMOS-compatible process. A micromachined inductor (L) and a pair of varactors (C) are developed in metal layers on a silicon substrate to realize the high quality factor LC-tank apparatus. This micromachined LC-tank apparatus is incorporated with CMOS transistor circuitry in order to realize a digital, tunable, low phase jitter, and low power clock, or time base, for synchronous integrated circuits. The synthesized clock signal can be divided down with digital circuitry from several GHz to tens of MHz—a systemic approach that substantially improves stability as compared to the state of the art. Advanced circuit design techniques have been utilized to minimize power consumption and mitigate transistor flicker noise upconversion, thus enhancing clock stability.

Claims

1. A MEMS-based, clock generation circuit for generating a highly stable, digital output signal without the need for external components, the circuit comprising:

a substrate;

an oscillator fabricated on the substrate and including a high-Q MEMS LC-tank apparatus for generating a periodic signal; and

first circuitry also fabricated on the substrate for converting the periodic signal into a high frequency digital output signal.

2. The clock generation circuit as claimed in claim 1 wherein the periodic signal is sinusoidal and has an original frequency and wherein the output signal is a square-wave signal having a frequency at half of the original frequency and wherein the circuit further comprises second circuitry also fabricated on the substrate for dividing the frequency of the square-wave digital output signal to at least one lower desired application frequency, thus reducing phase noise of the signal whereby stability is enhanced.

3. The clock generation circuit as claimed in claim 2 wherein the first and second circuitry and the oscillator are fabricated on the substrate with a CMOS-compatible process.

4. The clock generation circuit as claimed in claim 1 wherein both the oscillator and the first circuitry are fabricated on the substrate with a CMOS-compatible process.

5. The clock generation circuit as claimed in claim 4 wherein the CMOS-compatible process is a bulk or SOI CMOS process.

6. The clock generation circuit as claimed in claim 2 wherein the sinusoidal periodic signal is a differential signal and wherein the first circuitry converts the sinusoidal differential signal into a sinusoidal single-ended signal.

7. The clock generation circuit as claimed in claim 6 wherein the first circuitry also converts the sinusoidal single-ended signal into the square-wave digital output signal at half of the original frequency.

8. The clock generation circuit as claimed in claim 2 wherein the second circuitry includes at least one flip-flop coupled to the first circuitry for dividing the frequency of the square-wave digital output signal to the at least one lower desired application frequency.

9. The clock generation circuit as claimed in claim 1 wherein the substrate is a bulk or SOT substrate.

10. A MEMS-based, oscillator circuit for generating a low noise, high frequency, periodic signal, the oscillator circuit comprising:

a substrate;

a high-Q MEMS LC-tank apparatus fabricated on the substrate with a CMOS-compatible process; and

circuitry also fabricated on the substrate with the CMOS-compatible process and coupled to the LC-tank apparatus to generate the periodic signal.

11. The oscillator circuit as claimed in claim 10 wherein the frequency is variable to tune the oscillator circuit in response to a control input.

12. The oscillator circuit as claimed in claim 10 wherein the CMOS-compatible process is a bulk or SOI CMOS process.

13. The oscillator circuit as claimed in claim 10 wherein the oscillator circuit is a double-balanced oscillator circuit to reduce flicker noise upconversion.

14. The oscillator circuit as claimed in claim 11 wherein the LC-tank includes at least one micromachined varactor having a capacitance which varies in response to the control input.

15. The oscillator circuit as claimed in claim 14 wherein the at least one varactor includes a top plate and wherein the circuitry includes bypass capacitors to block the control input to the top plate from the remainder of the circuitry.

16. The oscillator circuit as claimed in claim 14 wherein the oscillator circuit is a double-balanced, cross-coupled oscillator circuit to reduce flicker noise upconversion.

17. A MEMS-based, LC-tank apparatus having a high quality factor, the apparatus comprising:

a substrate;

at least one micromachined varactor fabricated on the substrate with a CMOS-compatible process; and

a micromachined inductor coupled to the at least one varactor and also fabricated on the substrate with the CMOS-compatible process.

18. The apparatus as claimed in claim 17 wherein the at least one varactor has a variable capacitance to provide a tuning range for the apparatus.

19. The apparatus as claimed in claim 17 wherein the inductor is suspended above the substrate and released during or upon completion of the CMOS-compatible process.

20. The apparatus as claimed in claim 17 wherein the inductor is hollow.

21. The apparatus as claimed in claim 17 wherein the inductor is suspended above the substrate by anchors that are defined by the CMOS-compatible process.

22. The apparatus as claimed in claim 18 wherein the at least one varactor has a fixed bottom plate and a movable top plate suspended above the bottom plate and released during or upon completion of the CMOS-compatible process.

23. The apparatus as claimed in claim 22 wherein the top plate deflects based on a control input to tune the capacitance of the at least one varactor.

24. The apparatus as claimed in claim 22 wherein the top plate is suspended above the bottom plate by a mechanical suspension network defined by the CMOS-compatible process.

25. The apparatus as claimed in claim 17 wherein the at least one varactor and the inductor are defined by conductive layers in the CMOS-compatible process.

26. The apparatus as claimed in claim 25 wherein the conductive layers are metal layers.

27. The apparatus as claimed in claim 17 wherein the CMOS-compatible process is a bulk or SOI CMOS process.

28. The apparatus as claimed in claim 22 wherein the top plate has a plurality of etch holes to facilitate release of the top plate during or upon completion of the CMOS-compatible process.

29. The apparatus as claimed in claim 17 wherein the substrate is a bulk or SOI substrate.

30. The apparatus as claimed in claim 17 wherein the apparatus has a resonant frequency.

31. The apparatus as claimed in claim 17 wherein the at least one varactor and the inductor are defined by either MiM layers or two level metal routing layers.

32. A MEMS-based clock generation circuit for generating a highly stable, digital output signal, the circuit comprising:

an oscillator fabricated on a first substrate and including a high-Q MEMS LC-tank apparatus for generating a periodic signal; and

first circuitry fabricated on a second substrate for converting the periodic signal into a high frequency digital output signal.

33. A MEMS-based clock generation circuit as recited in claim 32 wherein the first and second substrates are distinct.

34. A MEMS-based clock generation circuit as recited in claim 32, wherein the first and second substrates the same such that the clock generation circuit is a monolithic circuit.

35. A computer system comprising:

a databus;

a central processing unit coupled bi-directionally to the databus;

transient memory coupled bi-directionally to the databus;

persistent memory coupled bi-directionally to the databus; and

a MEMS-based clock generation circuit for generating a highly stable, digital output signal suitable for use within said computer system, the clock generation circuit including;

an oscillator fabricated on a first substrate and including a high-Q MEMS LC-tank apparatus for generating a periodic signal; and

first circuitry fabricated on a second substrate for converting the periodic signal into a high frequency digital output signal.