This invention relates to microelectromechanical systems and more particularly to capacitive micromachined diaphragms, transducers, and ultrasonic transducers.
Over the past 20 years there has been intensive research on capacitive micromachined transducers (CMT), including capacitive micromachined ultrasonic transducers (CMUT), as compared with piezoelectric transducers (PZT), the lower mechanical impedance of CMT membranes offers the potential for a better impedance match with fluid media. Examples of CMT devices within the prior art include for example Chen et al in “Design and characterization of an air-coupled capacitive ultrasonic sensor fabricated in a CMOS process” (J. Micromechanics and Microengineering, Vol. 18); Doody et al “Modeling and Characterization of CMOS-Fabricated Capacitive Micromachined Ultrasound Transducers” (J. MEMS Systems, Vol. 20, pp. 104-118); Haller et al in “A surface micromachined electrostatic ultrasonic air transducer” (IEEE Trans. Ultrasonics Ferroelectrics and Frequency Control, Vol. 43, pp. 1-6) and Noble et al in “Low-temperature micromachined CMUTs with fully-integrated analogue front-end electronics” (IEEE Int. Ultrasonic Symp., Vol. 1-2, pp. 1045-1050). Further their performance is also less sensitive upon temperature, and they can be easily customized into 1 or 2 dimensional arrays. The fact that they are typically mass-produced using microfabrication techniques that are similar to those used in the semiconductor industry also enables the monolithic integration of CMT with integrated circuits (IC).
The advantages of monolithic integration of CMT together with IC are multiple: shared microfabrication equipment, combined process steps, shared layers, simplified packaging, and reduced die size by overlapping area with the electronics. Performance of the combined system is improved through a reduction of the parasitics, as a result of eliminating the chip-interconnecting wire bonds for example. Moreover, growing the CMT array directly on top of the electronics also allows the possibility of varying the phase of the excitation signal to each CMT element to enable beam-forming techniques. This would be essentially impossible if each element were to be connected to the IC with wire bonds. Among all schemes for integrating CMT directly with electronics, see for example Zahorian et al in “Single chip CMUT arrays with integrated CMOS electronics: Fabrication Process Development and Experimental Results” (IEEE Ultrasonics Symposium, Vol. 1-4, pp. 386-389) and Cheng in “CMUT-in-CMOS ultrasonic transducer arrays with on-chip electronics” (Transducers 2009, pp. 1222-1225), above-IC integration is a very attractive solution because it does not require any alteration of the semiconductor fabrication process. In fact, the CMT can be implemented as a subsequent process module, independent of the IC fabrication. Naturally, this scheme requires that the CMT technology limit itself to IC compatible materials and chemicals, as well as process step temperatures within a specific thermal budget.
Because of their superior mechanical properties and resistance to harsh environments such as high temperature, corrosive media and high-g shocks, silicon carbide (SiC) structures have been successfully used to build strain sensors, pressure sensors, and inertial sensors, see for example Muthu et al in “Silicon Carbide Microsystems for Harsh Environments” (Springer 2011). In the field of CMT, SiC has been demonstrated as an etch-stop layer, see for example Helin et al in “Poly-SiGe-based CMUT array with high acoustic pressure,” (25th Int. Conf. MEMS 2012, pp. 305-308), as a result of its chemical inertness. However, to the inventor's knowledge, CMT built using SiC structural membranes have not been implemented.
In order to make above-IC integration possible, SiC must be deposited at low temperatures. Typical deposition methods of SiC include plasma enhanced chemical vapour deposition (PECVD) and RF sputtering, see for example Ghodssi et al in “MEMS Materials and Processes Handbook” (Springer 2011). Recently, DC-sputtered amorphous SiC films have been used to fabricate high-quality beam resonators, see for example Nabki et al in “Low-Stress CMOS-Compatible Silicon Carbide Surface-Micromachining Technology—Part II: Beam Resonators for MEMS Above IC” (J. Microelectromechanical Systems, Vol. 20, pp. 730-744) (hereinafter Nabki1), RF switches, see for example Cicek et al in “Low actuation voltage silicon carbide RF switches for MEMS above IC” (16th IEEE Int. Conf. Elect., Circuits and Systems 2009, pp. 223-226) and vacuum sensors, see for example Taghvaei et al in “A MEMS-based temperature-compensated vacuum sensor for low-power monolithic integration” (IEEE Int. Symp. Circuits and Systems 2010, pp. 3276-3279). According to embodiments of the invention the inventors have expanded and development upon the surface micromachining technology of Nabki et al in “Low-Stress CMOS-Compatible Silicon Carbide Surface-Micromachining Technology—Part I: Process Development and Characterization” (J. Microelectromechanical Systems, Vol. 20, pp.720-729) (hereinafter Nabki2) to allow the fabrication of IC-compatible CMT structures.
Other aspects and features of the present invention will become apparent to those ordinarily skilled in the art upon review of the following description of specific embodiments of the invention in conjunction with the accompanying figures.
It is an object of the present invention to address limitations of the prior art relating to microelectromechanical systems and more particularly to capacitive micromachined diaphragms, transducers, and ultrasonic transducers.
In accordance with an embodiment of the invention there is provided a device comprising:
In accordance with an embodiment of the invention there is provided a device comprising a substrate, a lower electrode disposed on the substrate, and an upper electrode disposed upon the lower surface of a structural member formed above a predetermined portion of the lower electrode.
In accordance with an embodiment of the invention there is provided a device comprising:
Other aspects and features of the present invention will become apparent to those ordinarily skilled in the art upon review of the following description of specific embodiments of the invention in conjunction with the accompanying figures.
Embodiments of the present invention will now be described, by way of example only, with reference to the attached Figures, wherein:
The present invention is directed to microelectromechanical systems and more particularly to capacitive micromachined diaphragms, transducers, and ultrasonic transducers.
The ensuing description provides exemplary embodiment(s) only, and is not intended to limit the scope, applicability or configuration of the disclosure. Rather, the ensuing description of the exemplary embodiment(s) will provide those skilled in the art with an enabling description for implementing an exemplary embodiment. It being understood that various changes may be made in the function and arrangement of elements without departing from the spirit and scope as set forth in the appended claims.
A. Device Fabrication
A.1 Process Flow: Referring to
Within this embodiment of the invention a low-temperature-curable polyimide 130, PI-2555 from HD Microsystems, is employed as the sacrificial material. The precursor is first diluted in solvent (T-9030:HD Microsystems) at a 1:1 weight ratio, then spun onto the substrate, and cured at 200° C. for 2 hours. Reactive-ion etching (RIE) is used to pattern the polyimide with oxygen as depicted in second process step 100B. The final thickness of the layer is 450 nm, which establishes the dimension of the CMT electrostatic transduction gap. As depicted in first to sixth process steps 100A through 100F respectively a CMT 100 is depicted in first and second cross-sections X-X and Y-Y respectively.
A top electrode made of 60 nm-thick Al 110 is then sputtered and patterned as depicted in third step 100C. This is followed by the deposition of an 80 nm-thick chromium (Cr) 140 barrier layer, and the deposition and patterning of 300 nm-thick Al bond pads in fourth process step 100D. Next, a 2 μm-thick SiC 150 layer is deposited by DC sputtering and patterned as shown in fifth process step 100E. A metal film, such as Cr 140, can be used as an etch mask for the dry etching of the SiC film using fluorine-based RIE. At this point, the release access ports (holes or slits) to the sacrificial polyimide are also defined in the SiC 150 layer. The previously deposited Cr 140 barrier serves as an etch-stop layer during the SiC 150 dry etch step, in order to protect the underlying layers. After wet removal of the Cr 140 barrier, the SiN 120 layer is dry etched using the patterned SiC as the etch mask, so as to clear the pads for wire bonding. The substrate is then diced into individual CMT chips, which are finally released by removing the sacrificial polyimide in oxygen plasma for 6 hours, see sixth process step 100F.
In order to improve assembly throughput, an alternative sequence avoiding die-level sacrificial release can be used. This method involves the pre-grooving of the wafer substrate to half of its thickness, followed by a wafer level sacrificial release. Mechanical force is finally applied to cleave the wafer into individual dies.
A.2 Process Considerations: Due to the very low allowed thermal budget throughout the process flow presented in
The choice of polyimide (PI) 130 as a sacrificial material is also of importance. First, the ability to use a dry-release process eliminates the risk of stiction, which is common with wet release methods. Second, an oxygen plasma release, as opposed to a wet etching approach, such as hydrofluoric (HF) acid release, allows for the placement of the upper Al 110 electrode layer directly beneath the SiC membrane, without concerns of it being either attacked or deteriorated through the release process. This optimal proximity of the upper and lower electrodes reduces the transduction gap size, thereby improving electro-mechanical coupling and sensitivity of the CMT.
The design of the release ports is primarily dictated by the size of CMT membrane. Large membranes, for example 500 μm wide or above, generally require densely packed release holes in order to achieve reasonably fast release times, see for example
Since a low mechanical impedance of the membrane is beneficial for efficient ultrasonic power transfer in air, the CMUT prototype employed within the experiments were left unsealed to minimize mechanical loading. However, it would be evident that adding a low-stiffness sealing material, in order to mitigate squeeze-film damping and reduce particle contamination, would allow the CMUT devices to operate within liquid environments.
Now referring to
Next in fifth step 400E the electrode pads are formed by depositing and patterning an 80 nm Cr layer (omitted for clarity) and 300 nm Al3 450 layer. In sixth step 400F the SiC 460 structural layer is deposited and patterned via a Cr hard mask layer, for example 600 nm Cr, which is subsequently etched and removed after the SiC 460 has been patterned. Next in seventh step 400G the PI 430 is etched, releasing the CMT diaphragm. Subsequently a second SiN (SiN2) 470 layer is deposited in eighth process step 400H and patterned although alternatively a silicon oxide (SiO) or silicon oxynitride (SiON) layer may be employed for example.
Referring to
Referring to
It would be evident that alternatively other materials rather than silicon carbide may be employed as a sealing layer within CMT/CMUT devices according to embodiments of the invention. As noted a sealing layer allows the use of the CMT/CMUT in liquid media and ionized/partially ionized gaseous media. Optionally, parylene C, a poly(p-xylylene) polymer, would be a good candidate and alternative as a pinhole free insulator, with its very low moisture transmission rate (0.08 g·mm/m2·day) preventing liquid infiltration. Additionally, its low Young's modulus of 2.7 GPa reduces the sealing layers mechanical load on the CMT/CMUT membrane. For applications such as medical imaging that need to be in physical contact with objects, an additional soft protection layer covering the membrane array, such as an encapsulation made of polydimethylsiloxane (PDMS), a silicon-based organic polymer, may be deployed for example.
For vacuum sealing, the sealing layer may be achieved through a variety of techniques including, but not limited to, a high quality inorganic film deposited through PECVD, metal films through sputtering, or solder bumps reflowed in a vacuum environment. Parylene C films may also be employed for vacuum environment sealing provided that the deposition temperature of additional vacuum retention material doesn't surpass the glass transition temperature of Parylene C. A thin film deposited by atomic layer deposition (ALD) offers such a possibility where typical materials that can be deposited by ALD include, but are not limited to, oxides, e.g. alumina (A/2O3) and titania (TiO2), transition-metal nitrides, e.g. titanium nitride (TiN) and tantalum nitride (TaN) and metals, e.g. tungsten (W). Other deposition processes may allow the deposition of other metals and materials including, but not limited to, aluminum, chromium, titanium, tungsten, palladium, platinum, indium tin oxide, and gold.
As noted in respect of
Referring to Table 1 there are summarized the features of the CMT fabrication technology presented here according to an embodiment of the invention, compared to other reported surface-micromachined CMT processes specifically intended for above-IC integration. Owing to the deliberate selection of appropriate structural and sacrificial materials, the overall temperature budget of the fabrication technology in this work is the lowest reported to date. The high Young's modulus of the structural film, along with its very low residual stress, results in a very sturdy and resilient structure. In addition, the location of the upper electrode directly beneath the membrane brings closer the two capacitive plates therefore results in a more efficient electrostatic transduction gap as opposed to other implementations.
B: CMUT Modeling and Frequency Domain Studies
The theory and operating principles behind capacitive ultrasonic transducers have been well studied in literature, see for example Ladabaum et al in “Surface Micromachined Capacitive Ultrasonic Transducers” (IEEE Trans. Ultrason. Ferroelectr. Freq. Control, Vol. 45, pp. 678-690), Ergun et al in “Capacitive Micromachined Ultrasonic Transducers: Theory and Technology” (J. Aerosp. Eng., Vol. 16, pp. 76-84), and Cianci et al in “Fabrication Techniques in Micromachined Capacitive Ultrasonic Transducers and their Applications” (MEMS/NEMS, Springer-Verlag, 2006, pp. 353-382). Within the modelling presented here a small signal linear model is used to predict transducer performance in the frequency domain. To actuate a CMUT transmitter, a drive voltage V, consisting of a DC component, VDC, and an AC harmonic component, vac(t), is applied on the transducer to set the membrane in motion. The voltage applied is thus given by Equation (1) where ωi is the frequency of the AC voltage, and V0 its amplitude, which is considered to be much smaller than VDC. Modeling the CMUT as a parallel-plate capacitor, the electrostatic actuation force FE exerted on the membrane can be expressed as Equation (2), see Yue et al in “Nonlinear Dynamics Characterisation of Electrostatically Actuated Sub-Micro Beam Resonators” (Proc. SPIE Photoelectronic Detection and Imaging, Vol. 7381, 2009).
In Equation (2) ε0 is the vacuum permeability, d0 is the initial gap height, A is the plate area, x(t) is the vertical membrane displacement, and a first-order Taylor expansion is used for approximation. For a small-signal analysis, one can assume x<<d. Accordingly, the force associated with the AC voltage, i.e. the last term of Equation (2), drives the CMUT and launches ultrasonic waves into the environment.
For a CMUT receiver, only a DC voltage, VDC, is applied to the transducer. Ultrasonic waves carrying a pressure p(t) impinge onto the membrane, which causes a force that modulates the capacitance of the CMUT and generates an AC current. The total force acting on the membrane is given by Equation (3) while the output AC current I due to the capacitance variation is given by Equation (4).
where d is the gap height after the DC bias voltage VDC is applied and the harmonic vertical displacement x(t) is expressed as x0 sin(ωt).
From Equations (2) and (3), it can be observed that the total force exerted on the membrane for both the transmitting and receiving cases can be modeled as a load established by the transducer's DC operating point and a frequency-domain perturbation. Finite-element method (FEM) analysis was used to physically model the CMUT membranes, with the main objective of evaluating their displacement response in the frequency domain. The physical model of the membrane was simplified to a freestanding circular disk with 4 anchor points, according to the slit-type release port design shown earlier, While damping effects were taken into account through Rayleigh-type modeling, residual stress was neglected due to the inherent low stress of the material deposition recipes used in this process. The potential mechanical impacts of the upper electrode metal layers underneath the membrane were also neglected for simplification, as their thicknesses are much smaller compared to the SiC structural membrane.
Referring to
Using Equation (5), one may calculate the membrane impedance at the central point, by obtaining the amplitude of the displacement at that same point with a known pressure load.
C. Results and Discussion
A typical CMT test die and test structure are depicted in
C.1. Electrical Characterization of CMT Device: A vector network analyzer (VNA) was used to characterize the electrical insertion loss (s21) of the CMT operating in air.
When attempting to increase the DC bias above 40 V, breakdown of the interconnect-passivating silicon nitride dielectric was observed. This is attributable to the low breakdown voltage of the PECVD silicon nitride films used in the fabrication process. Consequently, the total instantaneous voltage applied to the CMUT transducers was kept below 40 V in all subsequent experiments.
Since the CMUT transducers testing were not sealed, the effect of squeeze-film damping when operating the device in air was investigated, as it could affect the quality (Q) factor and resonant frequency of the device. Accordingly, the impact of air damping on the Q-factor and resonant frequency of the CMUT transducers was verified by comparing the electrical insertion loss of the devices in air and in vacuum, as shown in
In comparison to the single-transducer Q-factor of 4.38 in air, eliminating squeeze-film damping yields a marginal improvement of the Q-factor to 4.56. This indicates that energy losses that dominate in this structure are linked to other mechanisms such as thermo-elastic damping or anchor losses, and thus the Q-factor is not significantly impacted by squeeze-film or viscous air damping.
While the Q-factor of the device cannot be used to clearly estimate the extent to which squeeze-film damping affects it, the resonant frequency shift that it exhibits between air and vacuum ambient conditions is more indicative. As can be seen in
It can be shown by finding the maxima of Equation (7) that the resonant frequency when taking into account squeeze-film damping is given by Equation (9) where ω0 is the resonant frequency of the CMUT without any damping (i.e., in vacuum). According to squeeze-film damping theory, see Bao, the large squeeze number (>>20) indicates that the squeeze-film damping is dominated by the elastic damping force, as opposed to a viscous damping force, due to the sufficiently fast air compression within the narrow transducer gap causing a compressible gas condition (i.e., operation beyond the squeeze number cut-off frequency). As such, this implies that kd/k in Equation (9) is sufficiently large to increase the resonant frequency in air, as seen in
For a sealed device, the vacuum region would only be situated on one side of the vibrating membrane, with the air environment on the other side, indicating that the frequency shift seen in
C.2. Acoustic Characterization of a CMT Device in Air: A pitch-and-catch configuration was used to test the acoustic behavior of the transducers in air. To achieve sufficient leveling and alignment between the active surfaces of the transmitter and receiver, an alignment system was built using kinematic mounting platforms, as shown on
The ultrasound radiation pattern was investigated by keeping the same pitch-and-catch configuration but displacing the CMUT receiver in the x, y, and z directions independently. The boundary for near field and far field of the CMUT transmitter was calculated to be around 16 mm, therefore the initial distance between the transmitter and the receiver was adjusted to be 22 mm, in order to ensure that the receiver was located within the far-field region of the emitted ultrasound wave. A 1.7 MHz sinusoidal wave with an amplitude of 20 V was used to excite the transmitter while a 20 V DC bias was applied to both transmitter and receiver. Again, a TIA was used for amplification of the received signal.
With above-1C integration in mind, the possibility of powering the CMUT using IC electronics was also investigated, through a series of tests using the pitch-and-catch system in CW mode. Lower biasing and actuation voltages, more suited to IC operation, were used. A maximum of 5 V was used as the DC bias for the transmitter and the receiver, as well as for the peak-to-peak AC signal at the transmitter.
D: Extensions
It would be evident to one skilled in the art that the first and second processing sequences depicted in
Now referring to
Accordingly, first and second CMT structures 2110 and 2130 may provide ultrasonic transmission of data between first circuit element 2160A in first substrate 2150 and third circuit element 2180A in second substrate 2170. Such data transmission may be unidirectional and/or bidirectional. In addition to direct communication first and second CMTs may provide characterization and assessment of a fluid between them or ultrasonic imaging based upon attenuation between elements of an array of transducers. Alternatively, a single integrated circuit with an array of CMT transceivers may be employed to provide ultrasonic imaging based upon pulsed operation of the CMT transceivers. Further, multiple CMTs may be combined with appropriate phase offsets to provide a beam-formed ultrasonic probe beam. Such an array of CMTs is depicted in
Accordingly, the inventors have demonstrated novel SiC-based CMT structures fabricated using an above-IC-compatible surface micromachining process. Further devices manufactured according to embodiments of the invention have been tested with IC-compatible voltage levels to validate their use in above-IC scenarios. Accordingly, the embodiments of the invention provide validation of the proposed fabrication technology and demonstrate the first SiC-based CMT. The low temperature, <200° C., of the manufacturing process, as well as its chemical compatibility, will enable the integration of CMT directly above-IC for smart and versatile ultrasonic systems, resulting in lower cost, smaller form factor and greater performance.
Whilst the embodiments of the invention described above in respect of
υ=√{square root over (E/ρ)} (11)
As evident from the material selection chart, different types of materials tend to be grouped together. Ceramic materials 2340 tending to appear in the top left, metals 2350 appearing in the middle-right, whilst polymers and elastomers 2320 are grouped together in the bottom-left. The trend arrow 2310 indicates the direction of preference for selecting materials for MEMS application in having high Young's modulus and low density. Accordingly, from the material selection chart alternatives to silicon (Si) for forming structural elements in resonant/acoustic/ultrasonic structures include silicon carbide (SiC) as discussed supra in respect of embodiments of the invention but also alumina (Al2O3), diamond (C), and silica nitride (Si3N4 or commonly SiN such as employed supra for simplicity). Accordingly, embodiments of the invention may also be implemented using designs and processes discussed supra in respect of
As discussed supra in respect of embodiments of the invention the CMT/CMUT devices in active device configurations require the interconnection of the CMT/CMUT device to an electrical circuit, e.g. bias voltage, data signal, pulse signal, etc. as well as routing from a sensor to post-processing circuitry. In some instances rather than a discrete CMT/CMUT device or a small number of relatively well separated CMT/CMUT devices there may be a large number of CMT/CMUT devices such as to provide a steerable ultrasonic output signal or a directionally settable receiver. In these instances a significant number of electrical connections may be necessary and require interconnection to control and processing electronics beside and/or below the CMT/CMUT device array.
The inventors have previously established innovative manufacturing sequences that are compatible with the process flows described supra in respect of in
Such metallization, via, feed-through and MEMS manufacturing process flows for example including U.S. Pat. No. 8,658,452 entitled “Low Temperature Ceramic Microelectromechanical Structures”, U.S. Pat. No. 8,071,411 “Low Temperature Ceramic Microelectromechanical Structures”, U.S. Pat. No. 8,409,901 entitled “Low Temperature Wafer Level Processing for MEMS Devices”, US Patent Application 2013/0,115,7530 entitled “Low Temperature Wafer Level Processing for MEMS Devices”
As noted supra in respect of descriptions and comments relating to embodiments of the invention and its concepts in respect of
E: Other Applications
Within the description supra in respect of
Examples of other applications of CMTs/CMUTs include, but are not limited to, those relating to:
Sonic Transducers: The CMTs by virtue of their flexibility in design with respect to diameter, geometry etc. may be designed to provide transducers for a wide range of frequencies. Consideration of equivalent circuit models of CMTs/CMUTs then there are several impedances, including membrane mechanical impedance, acoustic load impedance, and transducer losses, that are all dependent upon the area of the CMUT. Accordingly, the operating frequency can be rapidly varied through variations in the dimensions of the CMT/CMUT as for square and circular/hexagonal/octagonal etc. CMTs/CMUTs these will therefore vary according to a square law.
Acoustic Doppler Velocity Measurement: Integrated transmitter/receiver Doppler measurement devices may be implemented using CMUTs allowing non-optical based velocimetry techniques to be applied to a variety of test, measurement, analysis, and monitoring applications.
High-Temperature Non-Destructive Testing (NDT): Within the breadth of commercial sensor products those that operate at temperatures up to 250° C. are considered to be high-temperature sensors. Due to the properties of the CMTs/CMUTs in terms of a ceramic transduction element, e.g. SiC, and the potential to exploit silicon and other substrates including silicon-on-sapphire/silicon-on-insulator, and different metallization schemes then the CMUT devices manufactured according to embodiments of this invention will be able to withstand temperatures well above the 250° C. limit. In fact, these will generally be restrained by the melting point of the metallization layer used, which could be any metal that can be sputtered or evaporated. Accordingly, CMT/CMUT devices according to embodiments of the invention may be exploited for NDT applications in true high-temperature environments including, but not limited to, inside gas turbines, internal combustion engines, ovens, furnaces, combustion systems, distillation and cracking operations, etc.
Non-Contact NDT: Many samples to characterised should not be placed in direct contact with an ultrasonic transducer, for example due to an elevated surface temperature of the sample being characterised or non-compatibility of the sample with gel-type coupling layers normally employed. In contrast, low-impedance membrane-type CMUT devices provide an effective solution to this problem as the ambient air, instead of a gel, now serves to couple the transducers to the sample surface without contact. Additionally, due to the arrayed nature of the fabrication process measuring multiple locations of a sample is very quick without any mechanical impediment and/or motion requirement. This can have particular use in biomedical applications for instance.
Short-Range Distance Sensing: Short-distance measurement in air is usually difficult to achieve since, based on the time-of-flight principle, it requires the transducer to have a narrow pulse response and operate at a higher frequency to obtain sufficient measurement accuracy. The SiC-based CMUT developed in this work was able to measure several centimeters at a comparably high frequency. 1.7 MHz, in air. Whilst the CMTs/CMUTs would require design adjustments to match the specifications for real-world applications as outlined supra the operating frequency can be easily and rapidly scaled through simple dimensional adjustments. Further these devices allow the CMTs/CMUTs to be directly integrated with ICs, e.g. CMOS ICs as well as being formed into phased arrays thereby making these devices of interest in high-precision proximity sensors. One such are with large-scale deployment for such sensors is contactless gesture control for smartphones, tablets, and other hands free interfaces.
Gas Flow Rate Measurement: Within the prior art ultrasonic flow meters are known to exhibit inaccuracies due to high-frequency noise generated near pressure regulators in gas pipelines, in the range of 80-200 kHz, close to the working frequency of typical piezoelectric ultrasonic transducer. Accordingly, one solution to this issue is to use transducers operating at higher frequencies, making the measurement system less sensitive to the noise/acoustic interference, while also improving measurement accuracy. Accordingly, SiC-based CMUT developed in this work can help create more reliable flow meters in applications such as natural gas metering or industrial process control.
Measurement of Gas Leaks: In many applications leaks present a significant risk even at extremely low leaks. In many instances micro-cracks and other leak sources in combination with the flow of a liquid/gas through the leak will generate ultrasonic signals. Accordingly, CMUTs provide the ability to monitor high frequency leak generated ultrasonic waves in small footprint, low cost solutions allowing their deployment in a wide range of biochemical, pharmaceutical, chemical processing applications as well as general commercial/residential use.
Relative Humidity/Fluid Composition Sensing: The acoustic velocity of air varies with humidity. Similarly, the acoustic velocity of a fluid, e.g. one comprising two or more gases or liquids, may vary according to the composition of the fluid. Accordingly, this velocity variation can be determined using time of flight measurements from CMT/CMUT devices. Equally, the density of a fluid varies with temperature and accordingly CMT/CMUT time of flight data can be used to monitor fluid temperatures through NDT approaches.
Near-Field Data Transmission: In the majority of control and data applications despite the data rate of data transmission is quite low even if it is carried on wireless/microwave carriers. In many applications the communications are in fact required to be only short range/near field. Accordingly, ultrasonic transducers can be employed to transmit data at inaudible ranges over short ranges in a wide range of applications including sensor integration within personal area networks etc.
Specific details are given in the above description to provide a thorough understanding of the embodiments. However, it is understood that the embodiments may be practiced without these specific details. For example, circuits may be shown in block diagrams in order not to obscure the embodiments in unnecessary detail. In other instances, well-known circuits, processes, algorithms, structures, and techniques may be shown without unnecessary detail in order to avoid obscuring the embodiments. Implementation of the techniques, blocks, steps and means described above may be done in various ways. Also, it is noted that the embodiments may be described as a process which is depicted as a flowchart, a flow diagram, a data flow diagram, a structure diagram, or a block diagram. Although a flowchart may describe the operations as a sequential process, operations may in some instances be performed in parallel or concurrently. In addition, the order of the operations may in some instances be rearranged. A process is terminated when its operations are completed, but could have additional steps not included in the figure. A process may correspond to a method, a function, a procedure, a subroutine, a subprogram, etc. When a process corresponds to a function, its termination corresponds to a return of the function to the calling function or the main function.
The foregoing disclosure of the exemplary embodiments of the present invention has been presented for purposes of illustration and description. It is not intended to be exhaustive or to limit the invention to the precise forms disclosed. Many variations and modifications of the embodiments described herein will be apparent to one of ordinary skill in the art in light of the above disclosure. The scope of the invention is to be defined only by the claims appended hereto, and by their equivalents.
Further, in describing representative embodiments of the present invention, the specification may have presented the method and/or process of the present invention as a particular sequence of steps. However, to the extent that the method or process does not rely on the particular order of steps set forth herein, the method or process should not be limited to the particular sequence of steps described. As one of ordinary skill in the art would appreciate, other sequences of steps may be possible. Therefore, the particular order of the steps set forth in the specification should not be construed as limitations on the claims. In addition, the claims directed to the method and/or process of the present invention should not be limited to the performance of their steps in the order written, and one skilled in the art can readily appreciate that the sequences may be varied and still remain within the spirit and scope of the present invention.
This patent application claims the benefit of U.S. Provisional Patent Application US 61/781,886 filed Mar. 14, 2013 entitled “Methods and Devices relating to Capacitive Micromachined Diaphragms and Transducers.”
Number | Date | Country | |
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61781886 | Mar 2013 | US |