Apparatus and method capable of a high fundamental acoustic resonance frequency and a wide resonance-free frequency range

Abstract

An embodiment of the present invention provides an apparatus capable of a high fundamental acoustic resonance frequency, comprising a substrate, a bottom electrode layer adjacent the substrate, a voltage tunable dielectric layer adjacent the bottom electrode layer, the voltage tunable dielectric layer including an active region, a top electrode adjacent the voltage tunable dielectric layer, a final interconnect layer connected to the top electrode via an interlayer, and wherein the top and bottom electrodes are at a predetermined thickness such that a desired high fundamental acoustic resonance is obtained. The active region of the voltage tunable dielectric layer may be approximately the length of the top electrode and the interlayer and the final interconnect layer may cover only a small fraction of the active region of the voltage tunable dielectric layer, thereby reducing the amplitude of resonances due to the interlayer or final interconnect layer.

Description

BACKGROUND OF THE INVENTION [0001] Varactors are voltage tunable capacitors in which the capacitance is dependent on a voltage applied thereto. Although not limited in this respect, this property has applications in electrically tuning radio frequency (RF) circuits, such as filters, phase shifters, and so on. The most commonly used varactor is semiconductor diode varactor, which has the advantages of high tunability and low tuning voltage, but suffers low Q, low power handling capability, and limited capacitance range. A new type of varactor is a ferroelectric varactor in which the capacitance is tuned by varying the dielectric constant of a ferroelectric material by changing the bias voltage. Ferroelectric varactors have high Q, high power handling capacity, and high capacitance range. [0002] One ferroelectric varactor is disclosed in U.S. Pat. No. 5,640,042 entitled “Thin Film Ferroelectric Varactor” by Thomas E. Koscica et al. That patent discloses a planar ferroelectric varactor...

AI Technical Summary

Benefits of technology

[0006] An embodiment of the present invention provides an apparatus capable of a high fundamental acoustic resonance frequency, comprising a substrate, a bottom electrode layer adjacent the substrate, a voltage tunable dielectric layer adjacent the bottom electrode layer, the voltage tunable dielectric layer including an active region, a top electrode adjacent the voltage tunable dielectric layer, a final interconnect layer connected to the top electrode via an interlayer, and wherein the top and bottom electrodes are at a predetermined thickness such that a desired high fundamental acoustic resonance is obtained. The active region of the voltage tunable dielectric layer may be approximately the length of the top electrode and the interlayer and the final interconnect layer may cover only a small fraction of the active region of the voltage tunable dielectric layer, thereby reducing the amplitude of resonances due to the interlayer or final interconnect layer.

[0007] In an embodiment of the present invention, the substrate may be chosen to have a high acoustic loss factor thereby reducing the amplitude of resonances due to the substrate layer and the voltage tunable dielectric layer may be an approximately 300 nm thick BST layer matched with an approximately 150 nm gold top electrode and approximately 200 nm platinum bottom electrode and the interlayer and final interconnect layers may cover only a small percentage of the active region.

Problems solved by technology

The most commonly used varactor is semiconductor diode varactor, which has the advantages of high tunability and low tuning voltage, but suffers low Q, low power handling capability, and limited capacitance range.

However, the aforementioned thin BST layers are impractical due to manufacturability and linearity considerations.

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