Classifications

• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B06—GENERATING OR TRANSMITTING MECHANICAL VIBRATIONS IN GENERAL
  • B06B—METHODS OR APPARATUS FOR GENERATING OR TRANSMITTING MECHANICAL VIBRATIONS OF INFRASONIC, SONIC, OR ULTRASONIC FREQUENCY, e.g. FOR PERFORMING MECHANICAL WORK IN GENERAL
  • B06B1/00—Methods or apparatus for generating mechanical vibrations of infrasonic, sonic, or ultrasonic frequency
• • A—HUMAN NECESSITIES
  • A61—MEDICAL OR VETERINARY SCIENCE; HYGIENE
  • A61B—DIAGNOSIS; SURGERY; IDENTIFICATION
  • A61B8/00—Diagnosis using ultrasonic, sonic or infrasonic waves
  • A61B8/44—Constructional features of the ultrasonic, sonic or infrasonic diagnostic device
  • A61B8/4483—Constructional features of the ultrasonic, sonic or infrasonic diagnostic device characterised by features of the ultrasound transducer
• • H—ELECTRICITY
  • H01—ELECTRIC ELEMENTS
  • H01H—ELECTRIC SWITCHES; RELAYS; SELECTORS; EMERGENCY PROTECTIVE DEVICES
  • H01H59/00—Electrostatic relays; Electro-adhesion relays
  • H01H59/0009—Electrostatic relays; Electro-adhesion relays making use of micromechanics

Definitions

• electro-mechanical contactors are preferable in certain applications.
• One disadvantage of electronic switches results from leakage currents that cause finite current flow in the "OFF" position.
• electro-mechanical switches have a visible open position; no current flows in the "OFF” position.
• the isolation in mechanical relays is determined by the contact gap, and this distance can be adjusted to suit the isolation needs of a variety of applications.
• Protective relays should in any situation which occurs, be in a position to switch off and isolate the faulty circuit.
• Electronic components cannot fulfill this requirement because in case of electrical breakdown or thermal overload, they generally conduct current in both directions, and are no longer able to interrupt.
• mechanical relays instead of semiconductor switches, must be used for functions meant for safety.
• the preferred embodiments described below relate to an ultrasound system having the advantages of reduced size, reduced cost, improved signal integrity, reduced power consumption and higher-voltage pulsing capability. More particularly, the presently preferred embodiments relate to an improved ultrasound system incorporating micro-mechanical devices to replace "macroscopic" electro-mechanical devices in existing ultrasound designs. The presently preferred embodiments also relate to an ultrasound system which incorporates micro-mechanical devices to provide new functionality where existing electro-mechanical devices were inadequate. Given the ever-increasing bandwidth requirements of ultrasound systems coupled with their need for reduced size and cost, the potential has been recognized for micro-mechanical components to solve size, cost and power problems and allow for superior power-handling and gain the resulting superior system performance.
• the preferred embodiments described below apply the new technology of micro-mechanical devices to solve the lag in the rate of improvement of electro- mechanical devices.
• Figure 1A shows the first metal layer step of an exemplary fabrication process for an exemplary micro-mechanical switch for use in the preferred embodiments.
• Figure IB shows the sacrificial layer step of an exemplary fabrication process for an exemplary micro-mechanical switch for use in the preferred embodiments.
• Figure IC shows the sacrificial layer etching step of an exemplary fabrication process for an exemplary micro-mechanical switch for use in the preferred embodiments.
• Figure ID shows the beam masking step of an exemplary fabrication process for an exemplary micro-mechanical switch for use in the preferred embodiments.
• Figure IE shows the final etching step of an exemplary fabrication process for an exemplary micro-mechanical switch for use in the preferred embodiments.
• Figure 2A is a switching board of a preferred embodiment that can be used with an ultrasound system.
• Figure 2B is a replacement switching board of a preferred embodiment utilizing micro-mechanical switches or relays.
• Figure 3 is a substrate of a preferred embodiment incorporating both an ultrasound array and a micro-mechanical switching array in close proximity.
• Figure 4A depicts schematically how a switchable voltage bias may adjust the center frequency of a capacitive micro-mechanical ultrasound transducer (cMUT) of a preferred embodiment.
• Figure 4B depicts schematically a particularly preferred embodiment of the biasing of Figure 4 A utilizing a digital/analog (DAC) converter comprising micro- mechanical switches and resistors to control voltage bias applied to the cMUT(s) using a single source bias.
• Figure 4C depicts schematically a crossed electrode MUT transducer of a preferred embodiment wherein the voltage bias applied to various elevation subapertures may be switched using micro-mechanical micro-relays or micro- switches.
• DAC digital/analog
• Figure 4D depicts a 49 element two-dimensional transducer array of a preferred embodiment wherein each element is individually switchable using a micro-mechanical switch or relay. Central elements are biased to have higher frequencies than edge elements.
• the preferred embodiments relate to using micro-mechanical devices in ultrasound systems to overcome the problems of increasing size, cost and power handling that are occurring as systems designers attempt to add more value and more functionality to such systems.
• the preferred embodiments relate to the use of micro-mechanical devices coupled with individual acoustic elements, transducers, transducer cables, connectors and other components of ultrasound systems.
• the phrase "coupled with” is defined to mean directly coupled with or indirectly coupled with through one or more intermediate components.
• Micro-mechanical components are used to solve multiplexing issues created by high channel count requirements (wherein the ultrasound system is capable of sending and receiving to a high number of acoustic elements, 512 or greater), to provide higher power handling capabilities and to provide for smaller transducers with new capabilities.
• Micro-mechanics essentially involves making microscopic electro-mechanical devices of various sorts utilizing, at least in part, equipment and processes normally used to make integrated circuits on silicon, semiconductor or other dielectric wafers.
• equipment and processes normally used to make integrated circuits on silicon, semiconductor or other dielectric wafers.
• micro-devices are the millions of silicon-based accelerometer/switches made each year for automobile airbag passenger-restraint systems. Therein, that micro-device senses de- acceleration caused by a collision and deploys the airbag(s) by electrically activating a bag-inflation triggering charge.
• a micro-mechanical component or device (also known as a micro electro mechanical system (“MEMS” ) device) is defined as an electro-mechanical device where at least one mechanical or movable element of the component or device is manufactured (or “micro-machined”- see below) utilizing semiconductor-style processing.
• processing includes thin film deposition, patterning and etching techniques.
• Deposition techniques include both the physical deposition of material on a substrate and growth of a material on a substrate as are known in the art.
• Thin films created by such deposition techniques are generally on the order of 25 microns or less in thickness and typically 10 microns or less.
• Substrate materials can include semiconductor, ceramic or glass and can take the form of a wafer or other standardized form factor.
• Patterning techniques include lithographic patterning, printing or other form of pattern transfer, including mechanical pattern transfer, as are known in the art.
• Etching techniques include both chemical “wet” etching, plasma “dry” etching and laser etching as are known in the art.
• micro-machining is often used to refer to these semiconductor style processes utilized to fabricate micro-mechanical devices. Further, micro-machining includes both “bulk” micro-machining and “surface” micro-machining. Bulk micro- machining is the process of fabricating mechanical structures by etching the bulk of a substrate.
• Surface micro-machining is the process of fabricating mechanical structures on the surface of a substrate by deposition, patterning and etching layers of different materials and using other semiconductor style processes.
• FIG. 90 is shown in Figures 1 A- IE.
• the fabrication sequence begins with the deposition and patterning of the first metal layer 100 (chrome-gold) to define the gate 110 and contact electrodes 120 on the glass substrate 130 (see Figure 1A).
• a sacrificial metal layer 140 (copper) approximately 2 microns thick is then deposited ( Figure IB). This is patterned in 2 steps. In the first step, the sacrificial layer is partially etched to define the contact tips 150 for the beam 160 ( Figure IB). In the second etch step, the sacrificial layer 140 is etched all the way down to the source contact 100 metal to define the beam supports 170 ( Figure IC).
• photo-resist 180 is spun on top of the sacrificial layer 140 and patterned to define the mask for the beam structure 160.
• the beam 160 consists of a 2 micron thick layer of nickel 190 on top of a 200 nm thick layer of gold 200. Both these layers 190, 200 can be formed either by electroplating or by electroless plating ( Figure ID).
• the gold layer 200 serves as the contact material with the gold contact pads when the switch closes.
• the sacrificial layer 140 is removed by a suitable wet etching process to release the free-standing beam 160
• Micro-mechanical devices can be fabricated one at a time or in large numbers on a wafer (or substrate) of silicon, glass or ceramic-taking advantage of the batch-nature of semiconductor processing.
• the device can incorporate moving members such as deflecting micro- cantilevers, deflecting diaphragms, etc. as are known to the micro-mechanical art.
• the device can also incorporate a moving gas or fluid as in a micro-fluidic or micro-pneumatic device.
• the moving members of such devices can move by distortion, deformation, translation, deflection, rotation, torsion or other motion.
• micro-mechanical devices can incorporate at least one of electrostatic, magnetic, piezoelectric, electromagnetic, inertial, pneumatic, hydraulic or thermal micro-actuation mechanisms.
• Prototype micro- mechanical switches in particular have used electrostatic, magnetic, electromagnetic, thermal and inertial micro-actuation means.
• the possible micro- actuation mechanisms for switches and relays are therefor several and well known in the art, and therefore are not critical to the invention.
• the fact that such devices are employed in ultrasound applications in micro-mechanical form resulting in performance, cost, packaging and reliability advantages is the focus herein.
• Other micro-mechanical devices such as chemical sensors may have no physical/mechanical actuation means, and provide only a passive readout.
• micro-mechanical devices are provided to customers in the form of packaged chips.
• the chip-packages are typically IC-Chip packages (ceramic, plastic, metal etc) and each contains at least one and sometimes numerous devices.
• micro- mechanical switches and relays as the immediate preferred ultrasound-imaging embodiments, it is anticipated there are additional micro-mechanical applications in ultrasound, both electrical and mechanical, which this invention now makes recognizable.
• micro-mechanical inductors such as micro-mechanical inductors, micro-mechanical optical-fiber switches, micro-mechanical phase-shifters, micro-mechanical connectors (electrical, optical, hydraulic and pneumatic), micro-mechanical fuses and circuit-breakers, as well as micro- mechanical valves and micro-mechanical biometric user-identification devices such as the recently announced fingerprint pressure-sensing chips.
• micro-mechanics and current market projections for the micro-mechanical market particularly show the total micro-relay market to currently be in evolution, with full market- commercialization expected in the year 2006.
• electrostatically actuated micro-mechanical switches and relays resulting in likely fabrication processes and materials useful for making arrays of micro- mechanical switches which we see as applicable to ultrasound systems.
• micro-relays and nickel micro- relays There are references which describe work relating to micro-fuses, or more correctly micro-circuitbreakers for satellite applications, and references which describe work on contactless capacitive switch arrays in micro-mechanical form.
• micro-mechanical switch is a much more natural device for phase shifting. In essence, this is a miniaturized version of the venerable toggle switch so familiar in electronic components.
• micro-mechanical switches can also be beneficial as phase shifters, but in a different implementation than the planar case. Since planar arrays operate on the entire wave front, the micro-mechanical phase shifters can be added to each cell to introduce the proper amount of phase shift required to steer the beam. In many ways, this function is similar to that carried out in optics by a prism with the additional benefit that the difference between entry and exit angles of the beam is under electronic control. Further references provide overviews of micro-mechanical devices and describe work on micromachined silicon variable inductors and latching accelerometers. It is noted that such inductors are extremely attractive to ultrasound because of their low parasitics, excellent open-state isolation and their described programmability.
• micro-mechanical switches and/or relays relate to micro-mechanical switches and/or relays: (1) "Fully integrated magnetically actuated micromachined relays" by W. Taylor et al appearing in the Journal of Microelectromechanical Systems, June 01, 1998, v7 n2, pi 81 ; and (2) "Characteristics of micro-mechanical electrostatic switch for active matrix displays” by T. Nishio et al appearing in IEICE Transactions on Electronics, Sept 01, 1995, v78, n9, pl292.
• micro-mechanical devices offer many advantages, some of the main advantages are simply power handling, size and the ability to pack a lot of devices in a small area. With the ever increasing bandwidth needs of today's ultrasound systems, the ability to densely pack components capable of high power pulse manipulation is highly advantageous so as not to wind up with a system that is too unwieldy in both size and power use.
• switches located in the transducer itself such that the huge number of piezoelements may share (i.e. multiplex) a smaller and more reasonable number of cable wires.
• an array of switches may be provided in the transducer connector itself (at the system end of the transducer cable) in order to tie together (share) a first number of transducer piezoelements with a second differing number of available system channels. This approach can minimize transducer weight and power consumption because the user does not hold the switches in his/her hand while holding the probe. Further, by allowing for higher pulsing voltages addressed to an ever larger number of acoustic elements, currently weak harmonic acoustic signals and bandwidth can also be enhanced.
• FIG 2A shows a schematic (not to scale) of a prior-art system switching board 1 as described above.
• the board 1 is populated with a large number of prior-art relays 3, perhaps 128 or more, arranged on at least one of its two major surfaces.
• the board 1 is shown as having conventional edge-card connector contacts 5.
• a board is currently used having 128 SPDT (single pole double throw) relays 3.
• Such relays 3 can be purchased from vendors such as Omron, Hamlin, CP Clare and Cotto.
• Such prior-art relays 3 are each approximately 0.75 inch long by 0.25 inch wide by 0.25 inch tall thus their individual board footprint is approximately 0.75 by 0.25 inches.
• FIG. 1 shows the first major embodiment of the invention. Therein is shown a much smaller (relative to board 1) board 2 having two micro-mechanical micro-relay chips 4 each approximately 0.5-1.0 inches square as-packaged and surface-mounted on the board 2.
• each of these micro-mechanical relay chips 4 very easily contains 64 micro-relays each; thus this board 2 is the operational equivalent of the prior art board 1 yet is 5-10 times or more smaller, consumes far less power, is far less expensive and is capable of switching higher voltages, especially if the numerous micro-relays are ganged.
• Board 2 is also shown as having edge-card connections 6. Using the preferred embodiment described herein, the board 2 may have dimensions in the range of 2 or less inches tall by 6 or less inches wide. At the same time the electrical performance benefits mentioned earlier are gained over the conventional relay approach of the prior art board 1 and its devices 3.
• micro-relays are distinguished from micro-switches by the relationship between the actuator and the contacting functions. In a relay, the actuator and switching functions are separated and electrically isolated requiring a minimum of four terminals.
• a major variation on the first embodiment is to provide miniaturized micro-relay switching in the transducer itself (or in the transducer connector at the system-end of the transducer cable) for purposes of multiplexing a greater number of acoustic elements (or system channels) among a lesser number of transducer cable-wires.
• An existing state of the art transducer has a 256 wire cable and a 512 element acoustic array. At the current time this transducer requires two multilayer double-sided switching boards each about 2 by 3 inches in size to be packaged inside of it. These boards support 44 Supertex, Inc. switching chips, each such chip having 6 switches and having a 0.46 by 0.46 footprint. The same switching capability can be provided using one board about one-third the size with only a single-side mounting of one micro-relay-array chip. This represents a huge cost, power and performance advantage.
• FIG. 3 shows a co-integrated ultrasound array and micro-relay (or micro-switch) array.
• a transducer substrate 7 is shown which may be a silicon chip, silicon on glass, glass or ceramic substrate.
• An array of acoustic elements 8 is shown on the left side.
• An array of micro-relays 9 is shown on the right side. Sets of wirebond pads 10 are shown for purposes of connection to the outside world.
• a typical ultrasound application would have more piezoelements 8 than wires in the cable (cable wires attachable, for example, at bondpads 10) running to and from the transducer 7.
• the local micro-relays 9 would allow multiplexing or switching of the acoustic elements 8 among the lesser number of wires (wires would connect to bondpads 10). This is called multiplexing.
• a catheter-based transducer For a catheter-based transducer, one might have 8 wires in the cable (for reasons of low cost, small cross-section and flexibility) and have 256 acoustic elements 8 in the acoustic array being switched among the 8 wires (not shown) by 256 micro-relays 9. Obviously one might employ a variety of laparascopes or other low-cost tubular medical scopes for mounting such a transducer having integrated switching. Such co-integration would allow for such a reduced cost as to make a disposable version of such a catheter-based transducer possible. It is important to note several details about device 7. The first is that the acoustic elements 8 may be of any variety including thin- film elements (e.g.
• the array of elements 8 may take on any array geometry such as linear or two dimensional arrays.
• the micro-relays (or micro-switches) 9 may be on the same side (shown) or on the opposite face of the chip (not shown) and connected via wrap-around edge or through- via connections. They may also be intermixed within the acoustic element array.
• the fourth is that the means of external interconnection is not important and although wirebond pads 10 are indicated one may just as well utilize flip-chip or tape-automated bonding means.
• Device 7 may also, as desired, be joined or abutted to other useful acoustic components (not shown) such as matching layers, attenuative backers, isolation windows or acoustic lenses.
• useful acoustic components such as matching layers, attenuative backers, isolation windows or acoustic lenses.
• arrayed micromachined devices such as 4 and 9 may be any useful component, whether passive or active, wherein an acoustic array is being supported by one or more such micro-mechanically miniaturized devices and substantial space, power and cost is thereby being saved or signal integrity is improved.
• An excellent example of a component different than a switch or relay would be wherein each device 9 (or 4) is a micro-mechanical inductor or array of micro-mechanical inductors used for purposes of impedance matching the transducer to the system. In a manner similar to prior-art switches, prior-art inductors also consume huge amounts board space.
• device array 4 or device 7 may also attractively incorporate memory means used for storing transducer identification, transducer history, transducer beamforming microcode, transducer calibration information or the like.
• the returned harmonic signal can be relatively weak (relative to the transmitted fundamental frequency) and anything that can increase the returned harmonic signal's amplitude is highly attractive.
• the higher- voltage pulsing ability is also very useful when constructing sparsely populated two dimensional acoustic arrays (which are capable of volumetric 3D imaging) wherein one needs to maintain a good signal despite the leaving out of a good chunk of the elements (left out mainly for yield and cost reasons).
• Device 7 may utilize multilayer or laminated (interlayer electroded) piezoelements 8 as is known for improving impedance matching of the transducer to the system driving electronics.
• Elements 8 may also be arranged in multiple apertures (strips for example) such that said apertures can separately be switched on and off for purposes of narrowing the acoustic beam in the nearfield as has recently been practiced in the art.
• Elements 8, or groups thereof, may likewise be arranged to have differing acoustic performance or different electroacoustic or material properties.
• the next major preferred embodiment refers to a particular type of transducer acoustic element known as a MUT or a "micro-mechanical ultrasound transducer".
• a cMUT or capacitive (electrostatic) MUT is utilized.
• These are essentially electrically driveable vibrating micro- diaphragms or membranes made using micro-mechanical techniques wherein on each side of the vibrating diaphragm (membrane)/chamber is a capacitor electrode and the lateral (largest) dimensions of the diaphragm(s)/membrane(s) may be as small as in the micron range. Examples of such devices and processes necessary for their fabrication are known in the art.
• Figure 4A shows schematically one such element 8 which, in this example, is a micro-mechanical capacitive acoustic element or cMUT.
• element 8 which, in this example, is a micro-mechanical capacitive acoustic element or cMUT.
• FIG 4A shows schematically one such element 8 which, in this example, is a micro-mechanical capacitive acoustic element or cMUT.
• several voltage inputs 12,13...N which are each biasing source -means capable of providing a particular DC bias voltage to element 8.
• a DC blocking capacitor 16 is also provided as is an optional AC blocking unit 16a.
• the second bias voltage 13 (or both added together), is instead applied to element 8 causing element 8 to have a characteristic reception acoustic operating spectrum in the neighborhood of a desired (usually higher) harmonic receive-frequency.
• a desired (usually higher) harmonic receive-frequency For example the cMUT center transmit-frequency might be 3.5 MHz using bias 12 and the higher cMUT first-harmonic frequency might be 7.0 MHz using bias 13.
• Such frequency switching for harmonic imaging is known to the art.
• the transmit pulse voltage to the cMUT is applied in the presence of the first bias and acoustic receive is done using the second bias. It is apparent that one may alternatively have separate transmit and receive elements 8-ie dedicated elements. Further, there is no need to restrict the number of bias voltages to just two.
• Figure 4B depicts schematically a particularly preferred embodiment of the biasing of Figure 4 A wherein instead of using a discrete array of micro-mechanical switches to switch a number of fixed voltage bias sources ( Figure 4A), a digital/analog (DAC) converter comprising micro-mechanical switches and resistors is used wherein the micro-mechanical based DAC allows one to control voltage bias applied to the cMUT(s) using a single source bias.
• DAC digital/analog
• a cMUT is shown having a bias voltage control for varying the center frequency.
• a bias voltage source 12 routed to a DAC 17.
• control signals 18 By sending appropriate digital control signals 18 to the DAC 17 one controls the voltage bias being applied to cMUT 8 to be some portion of voltage 12.
• the bias 12 might be 200 volts and the DAC allows provision of 16 or 32 lesser reduced voltages.
• the DAC 17 itself may be constructed from micro-relays or micro-switches combined with resistors.
• the resistors may be laser-trimmed at manufacturing for extra precision during the setting of the values for each of the voltage choices.
• micro-mechanical techniques may be employed for both the acoustic element fabrication as well as fabrication of supporting electronic components.
• Figure 4C shows another application for micro-mechanical micro-relays or micro-switches.
• a plan view of a transducer array 23 is shown.
• the array 23 has orthogonal (or crossed) electrode sets.
• One electrode set 19 (19a, 19b, 19c....) addresses individual piezoelements linearly arrayed along the azimuth (top to bottom) direction.
• the other electrode set 20 (20a, 20b, 20c ....) addresses common subportions of the elevation of each piezoelement.
• the array is shown having a bias voltage source 12a and a means of bias control 22. It will be clear to those skilled in the art that with this electrode arrangement one may accomplish a variety of useful benefits.
• a first example is wherein the array consists of poled PZT piezomaterial and the micro-mechanical micro-relays are used simply to turn on and/or off various portions of the elevation length of all the elements thus obtaining a beneficial narrowing (or translation) of the elevation slice thickness either during transmit, receive or both-especially for near- in imaging.
• a second example is wherein the array consists of electrostrictive piezomaterial such as PZN whose acoustic response is maintained not by permanent poling but instead by application of a selectable temporary bias to achieve a selectable response level.
• the biasing takes the place of the permanent poling but the piezomaterial still needs to be pulsed for transmit
• Coax cables (wires or board traces) 21 are shown routed to the electrodes of the type 19a, 19b, 19c on each piezoelement.
• Figure 4D shows a square two-dimensional (2D) array consisting of a 7 by 7 array (or 49 total) of elements.
• the elements are labeled with the digits 1, 2, 3 or 4 as can be seen in the figure.
• the digits 1-4 represent four levels of center frequency as might be desired for a very broadband array. The levels can be distributed as shown with higher frequency (e.g. 4) in the center and lower frequency (e.g. 1) at the array's edges.
• Each cMUT acoustic element (49 total) in this array is addressable by at least one dedicated micro-relay or micro-switch and interconnect (not shown) capable of applying the desired bias level to its companion element.
• the benefits of frequency variation across an array are well known in the art.
• control the on/off state or the degree of electroacoustic activity e.g. using electrostrictive piezomaterial.
• micro-relays or micro-switches solves this problem both from the cost point of view as well as from the packaging and miniaturization point of view.

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