Classifications

• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B81—MICROSTRUCTURAL TECHNOLOGY
  • B81C—PROCESSES OR APPARATUS SPECIALLY ADAPTED FOR THE MANUFACTURE OR TREATMENT OF MICROSTRUCTURAL DEVICES OR SYSTEMS
  • B81C1/00—Manufacture or treatment of devices or systems in or on a substrate
  • B81C1/00015—Manufacture or treatment of devices or systems in or on a substrate for manufacturing microsystems
  • B81C1/00261—Processes for packaging MEMS devices
  • B81C1/00277—Processes for packaging MEMS devices for maintaining a controlled atmosphere inside of the cavity containing the MEMS
  • B81C1/00285—Processes for packaging MEMS devices for maintaining a controlled atmosphere inside of the cavity containing the MEMS using materials for controlling the level of pressure, contaminants or moisture inside of the package, e.g. getters
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B81—MICROSTRUCTURAL TECHNOLOGY
  • B81B—MICROSTRUCTURAL DEVICES OR SYSTEMS, e.g. MICROMECHANICAL DEVICES
  • B81B7/00—Microstructural systems; Auxiliary parts of microstructural devices or systems
  • B81B7/0032—Packages or encapsulation
  • B81B7/0035—Packages or encapsulation for maintaining a controlled atmosphere inside of the chamber containing the MEMS
  • B81B7/0038—Packages or encapsulation for maintaining a controlled atmosphere inside of the chamber containing the MEMS using materials for controlling the level of pressure, contaminants or moisture inside of the package, e.g. getters
• • 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
• • 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
  • B06B1/02—Methods or apparatus for generating mechanical vibrations of infrasonic, sonic, or ultrasonic frequency making use of electrical energy
  • B06B1/0292—Electrostatic transducers, e.g. electret-type
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B81—MICROSTRUCTURAL TECHNOLOGY
  • B81C—PROCESSES OR APPARATUS SPECIALLY ADAPTED FOR THE MANUFACTURE OR TREATMENT OF MICROSTRUCTURAL DEVICES OR SYSTEMS
  • B81C1/00—Manufacture or treatment of devices or systems in or on a substrate
  • B81C1/00015—Manufacture or treatment of devices or systems in or on a substrate for manufacturing microsystems
  • B81C1/00134—Manufacture or treatment of devices or systems in or on a substrate for manufacturing microsystems comprising flexible or deformable structures
  • B81C1/00158—Diaphragms, membranes
• • G—PHYSICS
  • G10—MUSICAL INSTRUMENTS; ACOUSTICS
  • G10K—SOUND-PRODUCING DEVICES; METHODS OR DEVICES FOR PROTECTING AGAINST, OR FOR DAMPING, NOISE OR OTHER ACOUSTIC WAVES IN GENERAL; ACOUSTICS NOT OTHERWISE PROVIDED FOR
  • G10K13/00—Cones, diaphragms, or the like, for emitting or receiving sound in general
• • H—ELECTRICITY
  • H04—ELECTRIC COMMUNICATION TECHNIQUE
  • H04R—LOUDSPEAKERS, MICROPHONES, GRAMOPHONE PICK-UPS OR LIKE ACOUSTIC ELECTROMECHANICAL TRANSDUCERS; ELECTRIC HEARING AIDS; PUBLIC ADDRESS SYSTEMS
  • H04R31/00—Apparatus or processes specially adapted for the manufacture of transducers or diaphragms therefor
  • H04R31/003—Apparatus or processes specially adapted for the manufacture of transducers or diaphragms therefor for diaphragms or their outer suspension
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B81—MICROSTRUCTURAL TECHNOLOGY
  • B81B—MICROSTRUCTURAL DEVICES OR SYSTEMS, e.g. MICROMECHANICAL DEVICES
  • B81B2201/00—Specific applications of microelectromechanical systems
  • B81B2201/02—Sensors
  • B81B2201/0271—Resonators; ultrasonic resonators
• • G—PHYSICS
  • G10—MUSICAL INSTRUMENTS; ACOUSTICS
  • G10K—SOUND-PRODUCING DEVICES; METHODS OR DEVICES FOR PROTECTING AGAINST, OR FOR DAMPING, NOISE OR OTHER ACOUSTIC WAVES IN GENERAL; ACOUSTICS NOT OTHERWISE PROVIDED FOR
  • G10K11/00—Methods or devices for transmitting, conducting or directing sound in general; Methods or devices for protecting against, or for damping, noise or other acoustic waves in general
  • G10K11/18—Methods or devices for transmitting, conducting or directing sound
  • G10K11/26—Sound-focusing or directing, e.g. scanning
  • G10K11/28—Sound-focusing or directing, e.g. scanning using reflection, e.g. parabolic reflectors
• • H—ELECTRICITY
  • H04—ELECTRIC COMMUNICATION TECHNIQUE
  • H04R—LOUDSPEAKERS, MICROPHONES, GRAMOPHONE PICK-UPS OR LIKE ACOUSTIC ELECTROMECHANICAL TRANSDUCERS; ELECTRIC HEARING AIDS; PUBLIC ADDRESS SYSTEMS
  • H04R19/00—Electrostatic transducers
  • H04R19/005—Electrostatic transducers using semiconductor materials

Definitions

• Patent Application Serial No. 62/738,502 filed September 28, 2018 under Attorney Docket No. B1348.70103US00, and entitled“FABRICATION TECHNIQUES AND STRUCTURES FOR GETTERING MATERIALS IN ULTRASONIC TRANSDUCER CAVITIES,” which is hereby incorporated herein by reference in its entirety.
• the present disclosure relates generally to micromachined ultrasound transducers and, more specifically, to fabrication techniques and associated structures for gettering materials present in ultrasound transducer cavities during manufacture.
• Ultrasound devices may be used to perform diagnostic imaging and/or treatment, using sound waves with frequencies that are higher with respect to those audible to humans.
• Ultrasound imaging may be used to see internal soft tissue body structures, for example to find a source of disease or to exclude any pathology.
• pulses of ultrasound are transmitted into tissue (e.g., by using a probe)
• sound waves are reflected off the tissue with different tissues reflecting varying degrees of sound.
• These reflected sound waves may then be recorded and displayed as an ultrasound image to the operator.
• the strength (amplitude) of the sound signal and the time it takes for the wave to travel through the body provide information used to produce the ultrasound images.
• Some ultrasound imaging devices may be fabricated using micromachined ultrasound transducers, including a flexible membrane suspended above a substrate.
• a cavity is located between part of the substrate and the membrane, such that the combination of the substrate, cavity and membrane form a variable capacitor.
• the membrane When actuated by an appropriate electrical signal, the membrane generates an ultrasound signal by vibration.
• the membrane In response to receiving an ultrasound signal, the membrane is caused to vibrate and, as a result, an output electrical signal can be generated.
• a method of forming an ultrasound transducer device includes bonding a membrane to a substrate so as to form a sealed cavity therebetween, wherein an exposed surface located within the sealed cavity comprises a getter material, the getter material being electrically isolated from a bottom electrode of the cavity.
• an ultrasound transducer device in another aspect, includes a membrane bonded to a substrate with a sealed cavity therebetween.
• An exposed surface located within the sealed cavity includes a getter material, the getter material being electrically isolated from a bottom electrode of the cavity.
• FIG. 1 is a cross-sectional view of a micromachined ultrasound transducer having a cavity getter material, in accordance with an embodiment.
• FIG. 2 is a top view of the ultrasound transducer of FIG. 1, taken along the arrows 2-2.
• FIG. 3 is a top view of the ultrasound transducer of FIG. 1, taken along the arrows 3-3.
• FIG. 4 is a cross-sectional view of a micromachined ultrasound transducer having a cavity getter material, in accordance with another embodiment.
• FIG. 5 is a top view of the ultrasound transducer of FIG. 4, taken along the arrows 5-5.
• FIG. 6 is a top view of the ultrasound transducer of FIG. 4, taken along the arrows 6-6.
• FIG. 7 is a cross-sectional view of a micromachined ultrasound transducer having a cavity getter material, in accordance with another embodiment.
• FIG. 8 is a top view of the ultrasound transducer of FIG. 7, taken along the arrows 8-8.
• FIG. 9 is a top view of the ultrasound transducer of FIG. 7, taken along the arrows 9-9.
• FIGs. 10-19 illustrate a process flow sequence for forming the ultrasound transducer embodiments of FIGs. 1-9, in which:
• FIG. 10 illustrates the formation of an electrode layer over a CMOS substrate.
• FIG. 11-1 illustrates patterning of the electrode layer of FIG. 10 according to the embodiment of FIG. 1.
• FIG. 11-2 illustrates patterning of the electrode layer of FIG. 10 according to the embodiment of FIG. 4.
• FIG. 11-3 illustrates patterning of the electrode layer of FIG. 10 according to the embodiment of FIG. 7.
• FIG. 12-1 illustrates forming an insulation layer over the structure of FIG. 11-1.
• FIG. 12-2 illustrates forming an insulation layer over the structure of FIG. 11-2.
• FIG. 12-3 illustrates forming an insulation layer over the structure of FIG. 11-3.
• FIG. 13-1 illustrates planarizing the insulation layer of the structure of FIG. 12-1.
• FIG. 13-2 illustrates planarizing the insulation layer of the structure of FIG. 12-2.
• FIG. 13-3 illustrates planarizing the insulation layer of the structure of FIG. 12-3.
• FIG. 14 illustrates forming an insulation stack over the structure of FIG. 13-1.
• FIG. 15 illustrates forming a cavity in the insulation stack.
• FIG. 16 illustrates removing a portion of the lower insulation layers of the insulation stack to expose adjacent electrode material that serves as a getter material.
• FIG. 17 illustrates a silicon-on-insulator (SOI) wafer to be bonded to the structure of FIG. 16.
• SOI silicon-on-insulator
• FIG. 18 illustrates the SOI wafer bonded to the structure of FIG. 16.
• FIG. 19 illustrates removing a portion of the SOI wafer to define a membrane of a micromachined ultrasound transducer.
• FIG. 20 illustrates a top view of an example ultrasound transducer device formed using any of the process flow sequences described herein.
• MUT micromachined ultrasound transducer
• MUTs may include capacitive micromachined ultrasound transducers (CMUTs) and piezoelectric micromachined ultrasound transducers (PMUTs), which can offer several advantages over more conventional ultrasound transducer designs such as, for example, lower manufacturing costs and fabrication times and/or increased frequency bandwidth.
• CMUTs capacitive micromachined ultrasound transducers
• PMUTs piezoelectric micromachined ultrasound transducers
• the basic structure is a parallel plate capacitor with a rigid bottom electrode and a top electrode residing on or within a flexible membrane. Thus, a cavity is defined between the bottom and top electrodes.
• the CMUT transducer may be directly integrated on an integrated circuit that controls the operation of the transducer.
• One way of manufacturing a CMUT ultrasound device is to bond a membrane substrate to an integrated circuit substrate, such as a complementary metal oxide semiconductor (CMOS) substrate. This may be performed at temperatures sufficiently low to prevent damage to the devices of the integrated circuit.
• CMOS complementary metal oxide semiconductor
• FIG. 1 there is shown a cross-sectional view of a
• the ultrasound transducer 100 includes a lower electrode 102 formed over a substrate 104 (e.g., a CMOS substrate, such as silicon).
• CMOS substrate 104 may include, but is not necessarily limited to, CMOS circuits, wiring layers,
• suitable materials for the lower electrode 102 include one or more of titanium (Ti), zirconium (Zr), vanadium (V), cobalt (Co), nickel (Ni), as well as alloys thereof.
• the lower electrode 102 is electrically isolated from adjacent metal regions 106 that are also formed on the substrate 104. Exposed portions of the adjacent metal regions 106 may thus serve as a getter material during cavity formation.
• the adjacent metal regions 106 may be formed from a same metal material as the lower electrode 102, and are electrically isolated from the lower electrode 102 by an insulator material 108 (e.g., silicon oxide).
• FIG. 2 is a top down view of the lower electrode, adjacent metal regions 106 and insulator material 108, taken along the arrows 2-2 in FIG. 1.
• an insulator layer e.g., one or more individual insulator layers, such as an insulator stack 110
• a moveable membrane 112 e.g., an SOI wafer having a doped silicon device layer with an oxidized surface
• the insulator stack 110 includes a first oxide layer 114 (e.g., chemical vapor deposition (CVD) silicon oxide), a second oxide layer 116 (e.g., atomic layer deposition (ALD) aluminum oxide) and a third oxide layer 118 (e.g., sputter deposited silicon oxide).
• a cavity 120 may be defined for the ultrasound transducer 100.
• the second oxide layer 116 is chosen from a material having an etch selectivity with respect to the third oxide layer 118, the second oxide layer 116 may serve as an etch stop for removing portions of the third oxide layer 118 in order to define the cavity 120.
• FIG. 3 A top down view of the cavity 120, illustrating remaining portions of the second oxide layer 116 and the exposed portions of metal regions is illustrated in FIG. 3, taken along the arrows 3-3 in FIG. 1.
• the exposed portions of metal regions 106 may advantageously serve as a getter material of one or more gases present during a bonding operation of the membrane 112 to seal the cavity 120. Additional exemplary processing operations used in forming the ultrasound transducer 100 are discussed hereinafter.
• FIGs. 4-6 illustrate a cross-sectional and top down views of a micromachined ultrasound transducer 400 having a cavity getter material, in accordance with another embodiment.
• like elements are designated by like reference numerals in the various embodiments. As particularly illustrated in FIG. 4 and in FIG. 5 (taken along the lines 5-5 in FIG.
• the lower electrode 102 is formed so as to have a“donut” pattern; that is, a region corresponding to the innermost radius of the electrode structure of the earlier described embodiment is instead formed from an insulating material (e.g., oxide 108) rather than the conductive electrode material.
• oxide layers 116 and 114 are only removed from the outer region of the cavity geometry, the top down view of FIG. 6 is substantially similar to that of the embodiment of FIG. 3.
• the electrode geometry of FIG. 4 may be employed in various operating modes, including in conjunction with a collapse mode of operation of the ultrasound transducer 400, where at least a part of the membrane 112 comes into physical contact with a bottom surface of the cavity 120 (for example, second oxide layer 116).
• a collapse mode of operation of the ultrasound transducer 400 where at least a part of the membrane 112 comes into physical contact with a bottom surface of the cavity 120 (for example, second oxide layer 116).
• substituting a central portion of the lower electrode material with an insulator material can help to reduce parasitic capacitance of the ultrasound transducer 400 without significantly compromising
• FIGs. 7-9 there is illustrated a cross-sectional and top down views of a micromachined ultrasound transducer 700 having a cavity getter material, in accordance with still another embodiment.
• like elements are designated by like reference numerals in the various embodiments.
• the lower electrode 102 is still formed so as to have a“donut” pattern.
• an additional electrode 702 is formed at the central portion of the cavity region.
• the electrode 702 is patterned to be electrically isolated from lower electrode 102, such as by being insulated therefrom by oxide 108 for example.
• the top down view of FIG. 9 is substantially similar to that of the embodiments of FIG. 3 and FIG. 6.
• Another benefit of electrode 702 may be to help provide for a lower collapse voltage for the ultrasound transducer 700 by way of the electrode 702 attracting the membrane 112 toward the bottom of the cavity 120. Additional information regarding this electrode design may also be found in the aforementioned co pending U.S. Patent Applications Serial Nos. 62/666,643 and 16/401,630.
• an electrode layer 1000 is formed over CMOS substrate 104, such as a silicon substrate for example.
• the CMOS substrate 104 may include, but is not necessarily limited to, CMOS circuits, wiring layers, redistribution layers, and insulation/passivation layers.
• suitable materials for the electrode layer 1000 include one more of titanium (Ti), zirconium (Zr), vanadium (V), cobalt (Co), nickel (Ni), as well as alloys thereof.
• FIG. 11-1 a photolithographic process is used to pattern and etch openings into the electrode layer 1000 so as to define the electrode pattern of FIG. 1, namely a lower electrode 102 and adjacent metal regions 106. In this particular embodiment, a center region of the lower electrode 102 remains intact.
• FIG. 11-1 a photolithographic process is used to pattern and etch openings into the electrode layer 1000 so as to define the electrode pattern of FIG. 1, namely a lower electrode 102 and adjacent metal regions 106.
• a center region of the lower electrode 102 remains intact.
• FIG. 11-2 illustrates the patterning of the electrode layer 1000 of the FIG. 4 embodiment (i.e., center portion of electrode removed to define a“donut” pattern)
• FIG. 11-3 illustrates the patterning of the electrode layer 1000 of the FIG. 7 embodiment (i.e., formation of the additional electrode 702 at the center portion of the donut pattern).
• the process may then proceed to an insulation fill operation as illustrated in FIGs. 12-1, 12-2 and 12-3.
• an insulation layer 1200 e.g., silicon oxide
• the insulation layer 1200 is then planarized as respectively shown in FIGs. 13-1, 13-2 and 13-3 to form the insulator material 108 described above. From this point, processing for each of the illustrated electrode design embodiments is substantially the same. Accordingly, the remaining figures are illustrated in the context of the first embodiment only (i.e., from FIG. 13-1) for conciseness, although it should be understood that the subsequent processes are equally applicable to the other embodiments.
• an insulator stack 110 as described above is formed over the lower electrode layer, such as the lower electrode 102 and adjacent metal regions 106 illustrated in FIG. 13-1.
• the insulator stack 110 includes a first oxide layer 114 (e.g., CVD silicon oxide having a thickness of about 1-100 nm) formed over the lower electrode 102 and adjacent metal regions 106, a second oxide layer 116 (e.g., ALD aluminum oxide having a thickness of about 5-100 nm) formed over the first oxide layer 114, and a third oxide layer 118 (e.g., sputter deposited silicon oxide having a thickness of about 1-300 nm) formed over the second oxide layer 116.
• a first oxide layer 114 e.g., CVD silicon oxide having a thickness of about 1-100 nm
• a second oxide layer 116 e.g., ALD aluminum oxide having a thickness of about 5-100 nm
• a third oxide layer 118 e.g., sputter deposited silicon oxide having
• a first lithographic patterning and etch process is performed to define the cavity 120 by removing a portion of the third oxide layer 118, using the second oxide layer 116 as an etch stop.
• aluminum oxide material of the second oxide layer 116 present at the bottom of the cavity 1500 may also help to reduce charging of a (subsequently formed) top membrane in the event the top membrane comes into contact with the second oxide layer 116 during device operation (e.g., such as during a collapse mode of transducer operation).
• a thin layer of aluminum oxide (not shown) and also a thin self-assembled monolayer (SAM) with a heptadecafluoro tetrahydrodecyl trichloro silane or dodecyltrichlorosilane precursor (not shown) may be formed on the second oxide layer 116 after patterning and before photoresist removal.
• a SAM formed at the bottom of the cavity 120 may help to reduce any stiction of the top membrane to the bottom of the cavity 120 in the aforementioned collapse mode of operation or other mode where the top membrane comes in physical contact with the bottom of the cavity 120.
• any suitable number of cavities and corresponding electrode structures may be formed (e.g., hundreds, thousands, tens of thousands, etc.)
• a second lithographic patterning and etch process is performed to expose the adjacent metal regions 106 at the outer perimeter of the cavity 120.
• the second etch removes a portion of the second oxide layer 116 and first oxide layer 114, stopping on the adjacent metal regions 106, which will serve as a getter material.
• the device as depicted in FIG. 16 is prepared for membrane bonding.
• a particular size or size range of the opening(s) formed through the second oxide layer 116 and first oxide layer 114 may be chosen based on one or more calculations on how much gas needs to be
• a determination of how much getter material area to be formed in each cavity may depend on factors such as for example, how much gas is released during the bonding process, the device lifetime, and the desirable cavity pressure after the getter is activated. Final pressure may be adjusted by getter activation, which in turn may be accomplished by annealing at elevated temperatures. In embodiments, it is generally preferable to have more exposed getter material than a targeted amount, rather than less exposed getter material than the target amount, since the annealing time could be shortened with the extra getter material.
• an example range of getter material area within this cavity for effective gettering maybe about 1 x 10 4 cm 2 to about 2.5 x 10 4 cm 2 .
• an inner radius n of the getter material is about 83 microns (pm)
• an outer radius n of the getter material is about 96 microns pm
• a transducer cavity radius G3 is about 98 pm.
• a substrate 1700 e.g., a silicon-on-insulator (SOI) substrate
• SOI silicon-on-insulator
• a handle layer 1702 e.g., a silicon layer
• a buried oxide (BOX) layer 1704 e.g., a silicon device layer
• An oxide layer 1708 may optionally be provided on a backside of the handle layer 1702.
• the silicon device layer 1706 may be formed from single crystal silicon and may be doped in some embodiments. Such doping may be highly doped P-type or, alternatively N-type, and may be uniform through the silicon device layer 1706 or patterned by implantation in certain regions.
• an oxide layer 1710 e.g., a thermal silicon oxide is formed on the silicon device layer 1706.
• the substrate 1700 is bonded to the substrate 104 and the aforementioned structures formed on the substrate 104.
• the oxide material of layer 1710 is bonded to the oxide material 118 by low temperature oxide bonding methods (e.g., below 450°C), which may prevent damage to circuitry of the substrate 104.
• low temperature oxide bonding methods e.g., below 450°C
• the metal surface of the adjacent metal regions 106 is exposed during bonding of the substrate 1700, the metal is able to consume gases such as oxygen, nitrogen, argon, water vapor, etc., resulting in a more uniform pressure across the various cavities 120 of the ultrasound device.
• the oxide layer 1708 and the handle layer 1702 are removed by a suitable technique (e.g., etching, grinding, etc.), thereby defining the membrane 112 discussed above and as illustrated in FIG. 19.
• a suitable technique e.g., etching, grinding, etc.
• the BOX layer 1704 may also be removed prior to additional processing, which may include suitable steps to complete final wiring, interconnect and/or packaging steps used to produce an ultrasound device.
• FIG. 20 illustrates a top view of an example ultrasound transducer device 2000 formed using any of the process flow sequences described herein.
• the transducer device includes an array of individual transducers 100, such as those described above.
• the specific number of transducers 100 shown in FIG. 20 should not be construed in any limiting sense, and may include any number suitable for a desired imaging application, which may be for example on the order of tens, hundreds, thousands, tens of thousands or more. It will be appreciated the above described gettering techniques are particularly beneficial with an increasing larger array, given the ability to provide a uniform cavity pressure across a wafer or die.
• FIG. 20 further illustrates an example location of metal 2002 that may distribute an electrical signal to the membranes (upper electrodes) of the transducers 100.
• the exemplary embodiments illustrate and describe a same bottom electrode metal material used as a getter material during membrane bonding
• other non-metallic or non-metallic alloy getter materials may also be used in a similar manner.
• graphite, phosphorous and/or certain salts may serve as a cavity getter material.
• other locations in addition to a cavity bottom are also contemplated.
• layers may be formed in a manner so as to have getter material disposed on cavity sidewalls and/or the membrane itself (top of sealed cavity) for gettering during membrane bonding. Such additional getter layer(s) may also be formed at a different level than the bottom electrode material.
• the above-described embodiments can be implemented in any of numerous ways.
• the embodiments may be implemented using hardware, software or a combination thereof.
• the software code can be executed on any suitable processor (e.g., a microprocessor) or collection of processors, whether provided in a single computing device or distributed among multiple computing devices.
• any component or collection of components that perform the functions described above can be generically considered as one or more controllers that control the above-discussed functions.
• the one or more controllers can be implemented in numerous ways, such as with dedicated hardware, or with general purpose hardware (e.g., one or more processors) that is programmed using microcode or software to perform the functions recited above.
• the terms“approximately” and“about” may be used to mean within ⁇ 20% of a target value in some embodiments, within ⁇ 10% of a target value in some embodiments, within ⁇ 5% of a target value in some embodiments, and yet within ⁇ 2% of a target value in some embodiments.
• the terms“approximately” and“about” may include the target value.

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