Oscillators – Solid state active element oscillator – Transistors
Reexamination Certificate
1999-10-05
2001-08-21
Kinkead, Arnold (Department: 2817)
Oscillators
Solid state active element oscillator
Transistors
C331S175000, C331S176000, C331S183000, C310S309000, C073S504140
Reexamination Certificate
active
06278337
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to the field of integrated circuits, and, more particularly, to an integrated circuit and method having oscillating capability.
BACKGROUND OF THE INVENTION
Electronic clocks or timekeepers which use oscillators controlled by quartz crystal vibrators to generate timing signals are widely known. These oscillators which are controlled by quartz crystal vibrators, however, have frequencies that vary in response to temperature changes, process variations, and aging. Various techniques associated with these oscillators have been developed for compensating for temperature and process variation and for aging. These oscillators, however, are often still expensive, often consume much more power than desired, and often fail to be as accurate as desired. Also, these oscillators are often not compatible with other integrated circuit manufacturing processes, such as those associated with very large scale integration (“VLSI”) and complimentary metal oxide semiconductor (“CMOS”) processes.
Capacitive based tunable micro-mechanical resonators or oscillators are also known. An example is shown in U.S. Pat. No. 5,640,133 by MacDonald et al. titled “Capacitance Based Tunable Micromechanical Resonators.” The resonator illustrated in this patent includes a mechanically movable component which is suspended for motion with respect to a substrate. The movable component is a microelectromechanical (“MEM”) elongate beam and includes laterally extending flexible arms which suspend the beam and mount the beam to an adjacent substrate. This resonator, however, includes complex electrostatic actuators for quickly tuning the resonance of the mechanical structure, can be expensive to manufacture, and is not practical for many applications.
SUMMARY OF THE INVENTION
With the foregoing in mind, the present invention advantageously provides an integrated oscillator and associated methods which are compatible with existing semiconductor manufacturing technology. The present invention also advantageously provides an integrated oscillator and methods having a greater tolerance for small critical dimensions. The present invention additionally provides a cost effective method of forming an integrated oscillator, such as for timekeeping applications, and increases the process yield of fully released resonating beams. The present invention further advantageously provides an integrated oscillator which eliminates the need for an external crystal oscillator and the packaging costs associated therewith. The present invention still further advantageously provides an integrated oscillator which has improved accuracy over quartz crystal oscillators.
More particularly, an integrated oscillator for providing clock signals preferably includes micro-mechanical oscillating means for providing an oscillating clock signal. The micro-mechanical oscillating means preferably includes a fixed conductive layer and an oscillating conductive layer overlying the fixed conductive layer in spaced relation therefrom and extending lengthwise generally transverse to a predetermined direction for defining a released beam for oscillating at a predetermined frequency. The released beam advantageously can include a plurality of openings formed therein. The plurality of openings extend from an upper surface of the released beam to a region defining the spaced relation underlying the released beam and positioned between the released beam and the fixed conductive layer. The release beam can also include trimmed released portions defining peripheries of removed portions of the oscillating layer. Clock signal controlling means is connected to the micro-mechanical oscillating means for controlling the micro-mechanical oscillating means and for generating clock signals therefrom. The clock signal controlling means preferably includes a first electrode connected to the fixed conductive layer and a second electrode connected to the oscillating conductive layer so that the fixed conductive layer and the oscillating conductive layer provide a capacitive-type field when a voltage signal is applied to the first and second electrodes.
According to another aspect of the present invention, the integrated oscillator preferably includes micro-mechanical oscillating means for providing an oscillating clock signal. The micro-mechanical oscillating means preferably includes a support layer, a fixed layer positioned on a support layer, remaining portions of a sacrificial layer positioned on portions of the fixed layer, and an oscillating layer positioned on the remaining portions of the sacrificial layer, overlying the fixed layer in spaced relation therefrom, and extending lengthwise generally transverse to a predetermined direction for defining a released beam for oscillating at a predetermined frequency. The spaced relation is preferably formed by removal of unwanted portions of the sacrificial layer. The integrated oscillator also preferably includes clock signal controlling means connected to the micro-mechanical oscillating means for controlling the micro-mechanical oscillating means and for generating clock signals therefrom.
According to yet another aspect of the present invention, an integrated oscillator for providing clock signals preferably includes first and second micro-mechanical oscillating means each for providing an oscillating clock signal and clock signal controlling means connected to the first and second micro-mechanical oscillating means for controlling each of the first and second micro-mechanical oscillating means and for generating respective clock signals therefrom. The clock signal controlling means preferably includes a first pair of electrodes connected to the first micro-mechanical oscillating means, a second pair of electrodes connected to the second micro-mechanical oscillating means, and aging compensating means responsive to both the first and second micro-mechanical oscillating means for compensating for aging of the first micro-mechanical oscillating means by using the oscillating frequency of the second micro-mechanical means as a reference frequency.
The present invention also includes methods of forming an integrated oscillator. A method preferably includes providing a clock signal controlling circuit region and forming a micro-mechanical oscillating region connected to the clock signal controlling circuit region. The micro-mechanical oscillating region is preferably formed by at least forming a first fixed conductive layer of material on a support, depositing a sacrificial layer on the first conductive layer, depositing a second conductive layer on the sacrificial layer, and removing at least unwanted portions of the sacrificial layer underlying the second conductive layer to release the second conducting layer to thereby define a released beam overlying the fixed conducting layer for oscillating at a predetermined frequency.
Another method of forming an integrated oscillator preferably includes providing a clock signal controlling circuit region and forming a micro-mechanical oscillating region connected to the clock signal controlling circuit region. The micro-mechanical oscillating region is preferably formed by at least forming a first fixed conductive layer of material on a support, forming a second conductive layer overlying and in spaced relation from the fixed conductive layer so as to define a released beam for oscillating at a predetermined resonant frequency, and trimming portions of the released beam to reduce mass of the released beam so as to tune the predetermined resonant frequency thereof.
The method can also include the micro-mechanical oscillating region further including forming remaining portions of a sacrificial layer on the first conductive layer and underlying the second conductive layer. The step of forming the second conductive layer can include forming a plurality of openings extending through the second conductive layer. The method can still further include removing at least unwanted portions of the sacrificial layer underlying the second conductive
Chan Tsiu Chiu
DeSilva Melvin Joseph
Sunkara Syama Sundar
Galanthay Theodore E.
Jorgenson Lisa K.
Kinkead Arnold
Regan Christopher F.
STMicroelectronics Inc.
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