STATEMENT OF RELATED APPLICATIONS

This application is a non-provisional of U.S. provisional patent application Ser. No. 62/373,668, filed Aug. 11, 2016, the disclosure of which is hereby incorporated herein by reference in its entirety. Subject matter disclosed herein also relates to the following three U.S. patent applications each filed or to be filed on Oct. 26, 2016: (1) U.S. patent application Ser. No. 15/334,511 entitled “Acoustic Resonator Devices and Methods Providing Patterned Functionalization Areas;” (2) U.S. patent application Ser. No. 15/334,482 entitled “Acoustic Resonator Devices and Methods with Noble Metal Layer for Functionalization;” and (3) U.S. patent application Ser. No. 15/334,528 entitled “Acoustic Resonator Devices and Fabrication Methods Providing Hermeticity and Surface Functionalization;” wherein the contents of the foregoing three U.S. patent applications are hereby incorporated by reference as if set forth fully herein.

TECHNICAL FIELD

The present disclosure relates to acoustic resonator devices, including acoustic wave sensors and fluidic devices suitable for biosensing or biochemical sensing applications.

BACKGROUND

A biosensor (or biological sensor) is an analytical device including a biological element and a transducer that converts a biological response into an electrical signal. Certain biosensors involve a selective biochemical reaction between a specific binding material (e.g., an antibody, a receptor, a ligand, etc.) and a target species (e.g., molecule, protein, DNA, virus, bacteria, etc.), and the product of this highly specific reaction is converted into a measurable quantity by a transducer. Other sensors may utilize a non-specific binding material capable of binding multiple types or classes of molecules or other moieties that may be present in a sample, such as may be useful in chemical sensing applications. The term “functionalization material” may be used herein to generally relate to both specific and non-specific binding materials. Transduction methods used with biosensors may be based on various principles, such as electrochemical, optical, electrical, acoustic, and so on. Among these, acoustic transduction offers a number of potential advantages, such as being real time, label-free, and low cost, as well as exhibiting high sensitivity.

An acoustic wave device employs an acoustic wave that propagates through or on the surface of a piezoelectric material, whereby any changes to the characteristics of the propagation path affect the velocity and/or amplitude of the wave. Presence of functionalization material on or over an active region of an acoustic wave device permits an analyte to be bound to the functionalization material, thereby altering the mass being vibrated by the acoustic wave and altering the wave propagation characteristics (e.g., velocity, thereby altering resonance frequency). Changes in velocity can be monitored by measuring the frequency, magnitude, or phase characteristics of the acoustic wave device and can be correlated to a physical quantity being measured.

In the case of a piezoelectric crystal resonator, an acoustic wave may embody either a bulk acoustic wave (BAW) propagating through the interior of a substrate, or a surface acoustic wave (SAW) propagating on the surface of the substrate. SAW devices involve transduction of acoustic waves (commonly including two-dimensional Rayleigh waves) utilizing interdigital transducers along the surface of a piezoelectric material, with the waves being confined to a penetration depth of about one wavelength.

BAW devices typically involve transduction of an acoustic wave using electrodes arranged on opposing top and bottom surfaces of a piezoelectric material. In a BAW device, three wave modes can propagate, namely, one longitudinal mode (embodying longitudinal waves, also called compressional/extensional waves), and two shear modes (embodying shear waves, also called transverse waves), with longitudinal and shear modes respectively identifying vibrations where particle motion is parallel to or perpendicular to the direction of wave propagation. The longitudinal mode is characterized by compression and elongation in the direction of the propagation, whereas the shear modes consist of motion perpendicular to the direction of propagation with no local change of volume. Longitudinal and shear modes propagate at different velocities. In practice, these modes are not necessarily pure modes as the particle vibration, or polarization, is neither purely parallel nor purely perpendicular to the propagation direction. The propagation characteristics of the respective modes depend on the material properties and propagation direction respective to the crystal axis orientations. The ability to create shear displacements is beneficial for operation of acoustic wave devices with fluids (e.g., liquids) because shear waves do not impart significant energy into fluids.

Certain piezoelectric thin films are capable of exciting both longitudinal and shear mode resonance, such as hexagonal crystal structure piezoelectric materials including (but not limited to) aluminum nitride (AlN) and zinc oxide (ZnO). To excite a wave including a shear mode using a piezoelectric material layer arranged between electrodes, a polarization axis in a piezoelectric thin film must generally be non-perpendicular to (e.g., tilted relative to) the film plane. In biological sensing applications involving liquid media, the shear component of the resonator is used. In such applications, piezoelectric material may be grown with a c-axis orientation distribution that is non-perpendicular relative to a face of an underlying substrate to enable a BAW resonator structure to exhibit a dominant shear response upon application of an alternating current signal across electrodes thereof. Conversely, a piezoelectric material grown with a c-axis orientation that is perpendicular relative to a face of an underlying substrate will exhibit a dominant longitudinal response upon application of an alternating current signal across electrodes thereof.

Typically, BAW devices are fabricated by micro-electro-mechanical systems (MEMS) fabrication techniques, owing to the need to provide microscale features suitable for facilitating high-frequency operation. In the context of biosensors, functionalization materials (e.g., specific binding materials, also known as bioactive probes or agents) may be deposited on sensor surfaces by microarray spotting (also known as microarray printing) using a microarray spotting needle. Functionalization materials providing non-specific binding utility (e.g., permitting binding of multiple types or species of molecules) may also be used in certain contexts, such as chemical sensing. Unfortunately, dimensional tolerances for microarray spotting are typically larger than dimensional tolerances enabled by MEMS fabrication techniques. An excess of specific binding material may reduce sensor response, such as by impairing a lower limit of detection. Separately, an excess of exposed non-specific binding material may lead to undesirable attachment of analyte when a device is in use.

When analytes are present in very low concentrations in fluid samples, and sensitivity to changes in adsorbed mass is non-uniform with respect to position over the surface of an active region of a MEMS resonator-based biosensor, it may be difficult to reliably promote high sensitivity to changes in adsorbed mass. Restated, it may be difficult to provide a large signal change from a small change in adsorbed mass. Such difficulty may be exacerbated when an analyte-containing fluid sample is supplied parallel to an upper surface of a top side electrode of a biosensor.

Accordingly, there is a need for MEMS resonators employing functionalization material, as well as fluidic devices and methods utilizing such resonators, that are capable of reliably providing enhanced sensitivity to adsorbed mass, and that are suitable for operation in the presence of analyte-containing fluid (e.g., liquid) samples for biosensing or biochemical sensing applications.

SUMMARY

The present disclosure provides a micro-electrical-mechanical system (MEMS) resonator device that is arranged over a substrate and that includes at least one functionalization material arranged over at least a central portion, but less than an entirety, of a top side electrode. For an active region that exhibits greatest sensitivity at a center point and reduced sensitivity along its periphery, omitting functionalization material over at least one peripheral portion of a resonator active region prevents analyte binding in regions of lowest sensitivity. Restated, providing functionalization material solely over a central portion of the resonator active region that exhibits greatest sensitivity provides a larger signal change from smaller changes in mass adsorbed by binding to the functionalization material. This may be particularly beneficial when a MEMS resonator-based sensing device is used with fluid samples containing analytes at very low concentrations. Adjusting dimensions and configuration of an area containing functionalization material relative to the active area may also enhance sensor response. For example, at least one functionalization material may extend a maximum length in a range of from about 20% to about 95% (or in subranges of from about 30% to about 95%, or from about 40% to about 90%, or from about 50% to about 90%) of an active area length and may extend a maximum width in a range of from about 50% to 100% (or in subranges of from about 60% to about 100%, or from about 70% to about 95%) of an active area width. When such a MEMS resonator device is incorporated into a fluidic device, directionality of an area containing functionalization material relative to a direction of analyte-containing fluid flow may also be selected to enhance sensor response, which may be important when an analyte is present at a very low concentration.

In one aspect, the disclosure relates to a micro-electrical-mechanical system (MEMS) resonator device including a substrate, a bulk acoustic wave resonator structure arranged over at least a portion of the substrate, and at least one functionalization material arranged over at least a central portion of a top side electrode. The bulk acoustic wave resonator structure includes a piezoelectric material, a top side electrode arranged over a portion of the piezoelectric material, and a bottom side electrode arranged between the piezoelectric material and the substrate, wherein a portion of the piezoelectric material is arranged between the top side electrode and the bottom side electrode to form an active region. The top side electrode includes an active area portion that overlaps the bottom side electrode and is coincident with the active region, the active area portion includes an active area width, and the active area portion includes an active area length extending perpendicular to the active area width. The at least one functionalization material extends a maximum length in a range of from about 20% to about 95% (or in subranges of from about 30% to about 95%, or from about 40% to about 90%, or from about 50% to about 90%) of the active area length and extends a maximum width in a range of from about 50% to 100% (or in subranges of from about 60% to about 100%, or from about 70% to about 95%) of the active area width.

In certain embodiments, the maximum width of the at least one functionalization material exceeds the maximum length thereof.

In certain embodiments, the MEMS resonator device further includes a self-assembled monolayer (SAM) arranged between the top side electrode and the at least one functionalization material. In certain embodiments, the MEMS resonator device further includes an interface layer (e.g., including an oxide layer, a nitride, or an oxynitride material) arranged between the top side electrode and the at least one functionalization material.

In certain embodiments, the top side electrode comprises a non-noble metal, and the MEMS resonator device further includes a hermeticity layer arranged between the interface layer and the top side electrode. If provided, a hermeticity layer preferably includes a dielectric material with a low water vapor transmission rate (e.g., no greater than 0.1 g/m2/day). In certain embodiments, a self-assembled monolayer is arranged between the interface layer and the at least one functionalization material. In certain embodiments, the MEMS resonator device further includes a blocking layer arranged over a portion of the piezoelectric material non-coincident with the active region, wherein the presence of the blocking layer may serve to prevent binding of one or more species.

In certain embodiments, the at least one functionalization material comprises a specific binding material. In certain embodiments, the at least one functionalization material comprises a non-specific binding material.

In certain embodiments, the piezoelectric material comprises a c-axis having an orientation distribution that is predominantly non-parallel to normal of a face of the substrate.

In certain embodiments, the MEMS resonator device further includes at least one acoustic reflector element arranged between the substrate and the bulk acoustic wave resonator structure, such as to form a solidly mounted resonator structure. In other embodiments, the substrate defines a recess, and the MEMS resonator device further comprises a support layer arranged between the bulk acoustic wave resonator structure and the recess, wherein the active region is arranged over at least a portion of the support layer and at least a portion of the recess, such as to form a film bulk acoustic resonator (FBAR) structure.

In another aspect, the disclosure relates to a sensor and/or a fluidic device including a MEMS resonator device as disclosed herein. In one embodiment, a fluidic device comprising a MEMS resonator device includes a fluidic passage containing the active region and arranged to conduct a flow of liquid to contact the at least one functionalization material, wherein the fluidic passage is arranged to conduct the flow of liquid from an inlet port upstream of the active region toward the active region in a direction that is substantially parallel to the active area length. In certain embodiments, the at least one functionalization material is arranged in a shape comprising a leading edge (which may be straight, curved, angled, sawtooth, or another suitable shape), wherein a center point of the leading edge is arranged between the inlet port and a center point of the active region.

In another aspect, the disclosure relates to a method for biological or chemical sensing including a fluidic device as disclosed herein. One method step includes supplying a fluid containing a target species into the fluidic passage of the fluidic device, wherein said supplying is configured to cause at least some of the target species to bind to the at least one functionalization material. Additional method steps include inducing a bulk acoustic wave in the active region, and sensing a change in at least one of a frequency property, a magnitude property, or a phase property of the bulk acoustic wave resonator structure to indicate at least one of presence or quantity of target species bound to the at least one functionalization material.

In another aspect, the disclosure relates to a method for fabricating a micro-electrical-mechanical system (MEMS) resonator device. One method step includes forming a bulk acoustic wave resonator structure including a piezoelectric material, a top side electrode arranged over a portion of the piezoelectric material, and a bottom side electrode arranged between the piezoelectric material and a substrate, wherein a portion of the piezoelectric material is arranged between the top side electrode and the bottom side electrode to form an active region, the top side electrode comprises an active area portion that overlaps the bottom side electrode and is coincident with the active region, the active area portion includes an active area width, and the active area portion includes an active area length extending perpendicular to the active area width. Another method step includes depositing at least one functionalization material arranged over at least a central portion of the top side electrode, wherein the at least one functionalization material extends a maximum length in a range of from about 20% to about 95% (or in subranges of from about 30% to about 95%, or from about 40% to about 90%, or from about 50% to about 90%) of the active area length and extends a maximum width in a range of from about 50% to 100% (or in subranges of from about 60% to about 100%, or from about 70% to about 95%) of the active area width.

In certain embodiments, the foregoing method further includes forming a self-assembled monolayer over at least a portion of the top side electrode prior to said depositing of the at least one functionalization material, wherein the at least one functionalization material is arranged over at least a portion of the self-assembled monolayer. In certain embodiments, the forming of a self-assembled monolayer over at least a portion of the top side electrode comprises multiple steps, including (i) applying the self-assembled monolayer over the top side electrode; (ii) arranging a first mechanical mask over the self-assembled monolayer, wherein the first mechanical mask defines at least one first aperture through which at least one first portion of the self-assembled monolayer is exposed; and (iii) transmitting electromagnetic radiation comprising a peak wavelength in a range of from about 150 nm to 400 nm through the at least one first aperture to interact with the at least one first portion of the self-assembled monolayer to promote removal of the at least one first portion of the self-assembled monolayer. In certain embodiments, a method further includes arranging a second mechanical mask over at least a portion of the bulk acoustic wave resonator structure including the active region, wherein the second mechanical mask defines at least one second aperture through which at least one second portion of the self-assembled monolayer is exposed; and applying a blocking layer through the at least one second aperture to the at least one second portion of the self-assembled monolayer. Certain embodiments further include a step of forming at least one wall over a portion of the bulk acoustic wave resonator structure and defining a fluidic passage overlying the active region, wherein the fluidic passage is arranged to conduct a flow of liquid from an inlet port upstream of the active region toward the active region in a direction that is substantially parallel to the active area length, and the fluidic passage is arranged to conduct the flow of liquid to contact the at least one functionalization material.

In another aspect, any of the foregoing aspects, and/or various separate aspects and features as described herein, may be combined for additional advantage. Any of the various features and elements as disclosed herein may be combined with one or more other disclosed features and elements unless indicated to the contrary herein.

Those skilled in the art will appreciate the scope of the present disclosure and realize additional aspects thereof after reading the following detailed description of the preferred embodiments in association with the accompanying drawing figures.

