`
`SILICON MICROMACHINED CAPACITIVE PRESSURE SENSORS FOR
`
`INDUSTRIAL AND BIOMEDICAL APPLICATIONS
`
`A THESIS SUBMITTED TO
`
`THE GRADUATE SCHOOL OF NATURAL AND APPLIED SCIENCES
`
`OF
`
`THE MIDDLE EAST TECHNICAL UNIVERSITY
`
`BY
`
`ORHAN SEVKET AKAR
`
`IN PARTIAL FULFILLMENT OF THE REQUIREMENTS FOR THE
`
`DEGREE OF
`
`MASTER OF SCIENCE
`
`IN
`
`THE DEPARTMENT OF ELECTRICAL AND ELECTRONICS ENGINEERING
`
`SEPTEMBER 1998
`
`
`
`w¥a KQTEEHANESF
`3-1!
`rs, v!
`:1
`5 amgggmv
`M
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`Abbott
`Exhibit 1010
`Page 001
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`

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`
` : :' iii-Approval of Graduate School of Natural and Applied Sciences.
`
`
`
`Prof. Dr. Tayfur OZTURK
`
`Director
`
`I
`
`.'
`
`I certify that this thesis satisfies all the requirements as a thesis for the degree of
`
`Master of Science.
`
`‘L
`
`Prof. Dr. Fatih CANATAN
`
`Head of Department
`
`We certify that we have read this thesis and that in our opinion it is fully adequate, in
`
`scope and quality, as a thesis for the degree of Master of Science.
`
`T‘s—5'
`
`-
`
`Asst. Prof. Dr. Tayfun AKIN
`
`Supervisor
`
`:3
`1%; E
`Mm W187
`
`
`‘ U
`
`ELF
`
`Examining Committee Members:
`
`Prof. Dr. Ersin TULUNAY (Chairman)
`Prof. Dr. Murat ASKAR
`.
`
`Asst. Prof. Dr. Tayfun AKIN
`
`Asst. Prof. Dr. CengizBESIKCI
`
`Mr. Malik AVIRAL (ELIMKO AS.)
`
`
`
`
`
`Abbott
`Exhibit 1010
`Page 002
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`

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`
`
`ABSTRACT
`
`SILICON MICROMACHINED CAPACITIVE
`
`PRESSURE SENSORS FOR INDUSTRIAL AND
`
`BIOMEDICAL APPLICATIONS
`
`Akar, Orhan Sevket
`
`M.Sc., Department of Electrical and Electronics Engineering
`
`Supervisor: Asst. Prof. Dr. Tayfun Akm
`
`September 1998, 84 pages
`
`This thesis demonstrates the design and fabrication of two type of
`
`rnicromachined
`
`capacitive
`
`pressure
`
`sensors
`
`for
`
`industrial
`
`and
`
`biomedical
`
`applications.
`
`The fabricated pressure sensors are based on the deflecting
`
`micromachined thin silicon diaphragm anchored to glass substrate, forming variable
`
`capacitor with the applied pressure. Silicon micromachining process allows the
`
`implementation of thousands of pressure sensors on the same wafer, which is the
`
`main reason for low cost production, similar to the reason for low cost in the
`
`integrated circuit process.
`
`In the scope of this study,
`
`first, a number of silicon micromachining
`
`techniques have been developed, inciuding bulk micromachining boron etchwstop,
`
`iii
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`Exhibit 1010
`Page 003
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` and dissolved wafer process
`
`techniques.
`
`Then, by gaining experience on
`
`
`
`I
`
`inicrornachined pressure sensor design, a sensor block consisting of twelve capacitive
`
`pressure sensors have been designed and batch fabricated for six different pressure
`I ranges. The design of the sensors have been compieted in Department of Electrical
`
`and Electronics Engineering at Middle East Technical University, and fabricated in
`
`Solid-State Electronics Laboratory at The University of Michigan.
`
`The bulk
`
`. micromachining technology and the boron etch-stop dissolved wafer process have
`
`been successfully utilized in device fabrication. The dynamic ranges of the sensors
`
`designed for industrial applications vary between O-SOmran and 0-1200n1ran over
`atmospheric pressure, and each sensor occupies an area of 3.2 x 1.8 rnrnz. The new
`
`sensor structure for biomedical appiications can be implanted in the body and can be
`
`monitored telemetrically without using any wire that breaks the skin. This is
`
`achieved by using a gold electroplated coil, which is fabricated together with the
`
`pressure sensor. This implentabie sensor measures i.5mm x 2.5mm X 0.5mm in size
`
`and provides a dynamic range of 0-50mmHg over atmospheric pressure.
`
`A test setup has been prepared for the pressure sensor characterization. The
`
`measurements show the pressure sensor results in 175fF capacitance change for 0-
`
`200n1mHg range over l645fF zero pressure capacitance.
`
`This research is the first national study on the design and implementation of
`
`silicon micromachined capacitive pressure sensors.
`
`Keywords:
`
`silicon micromachining, capacitive pressure sensor, planar
`
`integrated coil.
`
`iv
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`Abbott
`Exhibit 1010
`Page 004
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`

`

`(")z
`
`siLiSYUM MiKRoisLEME YONTEMi iLE URETiLEN
`
`ENDi‘JSTRiYEL VE BiOMEDiKAL UYGULAMALAR
`
`iciN KAPAsiTiF BASINC SENSORLERi
`
`Akar, Orhan Sevket
`
`Yfiksek Lisans, Elektrik ve Elektronik Mfihendisligi Bdlfimfi
`
`Tez Ybneticisi: Yrd. Dog. Dr. Tayfun Akln
`
`Eyliil 1998, 84 sayfa
`
`Bu tezde endfistriyel ve biyomedikal uygulamalar iqin, silisyum mikroi§leme
`
`yb'ntemi ile firetilen iki tip basmt; sens'drfi anlatflmaktadu. Uretilen basmc; sens‘drii
`
`cam taban tizerinde, kenarlarl sabit mikroi$lenmi$ diyaframm olugturdugu kapasite
`
`degeriuin basmg: altmda degi§mesi prensibine dayanmaktadu'.
`
`Mikroizfileme
`
`teknikleri, tipkl entegre devre firetiminde oldugu gibi, bu tip basmg, sensérlerinin
`
`biniercesim'n aym pul fizerinde gok ucuza firetflmesini saglamaktadlr.
`
`Bu arastlrma Qergevesinde ilk olarak, gévde mikroisleme, pul agmdirma ve
`
`aslnmanln bor katkllanarak durdurulmam tekniklerinden olugan silisyum mikroi$ieme
`
`Abbott
`Exhibit 1010
`Page 005
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`

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`
`
`teknikleri
`
`geli§ti1‘ildi. Mikroi$lenmi$
`
`basmg
`
`senséjrii
`
`tasanmmda kazamlan
`
`deneyimle, altl farkh gailgima araligmda galigan oniki farkli kapasitif basmg sensiir‘u
`tasarlanm1$ ve aym anda firetimi gergeklefiirilmistir. Senséirler, Orta Dogu Teknik
`
`Universitesi Elektrik ve Elektronik Mfihendisligi Bélfimfi’nde tasarlanm1$ vs
`
`Michigan Universitesi Kan-Hal Elektronigi Laboratuvari’nda Uretilmi§tin Gévde
`
`mikmi§1eme teknolojisi ve pul
`
`a$1nd1rmas1nm bor katklsl
`
`ile durdumlmam,
`
`sensérlerin firetiminde ba§ar1 ile kullan11m1$tm
`
`Endfistriyel uygulamalar
`
`igin
`
`tasarlanan sensérlerin dinamik galmma arahklarl normal hava basmm fizerine 0-
`
`SOmmHg ve 0-1200mmHg arasmda degigmekte ve her bir sensiir 3.2 x 1.8111312 alan
`
`kaplmnaktadir. Ayrica, biyomedikal uygulamalarda kullamlmak fizere yeni bir
`
`sensér yaplsi gelifiirilmigtir.
`
`Yeni
`
`tasarlanan sensér
`
`insan viicudu igine
`
`yerlegtirilebilir ve bu yapi ile vijcuda giren tel baglantllan olmadan, uzaktan algzlama
`
`yb‘n’cemi ile élgfimler yapllabiiir. Bu ézellik senstir ile birlikte firetilen ve sensfjrfin
`
`igincle bulunan, elektrokaplama telmigi
`
`ile firetilmis bir bobin yardlmi
`
`ile
`
`saglmnnaktadlr. Vficut igine yerle$tirilebiiir sensiiriin boyutlan 1.5mm x 2.5 mm x
`
`0.5mm’dir ve dinamik galignla araligi O—SOmmHg’dir.
`
`Uretilen basmg:
`
`sensc'jrlerinin karakterizasyonu igin bir
`
`test diizenegi
`
`hazn'lanmngnr. Bu diizenelc ile yap1lan tastier sonucunda 1645fF nominal kapsite
`
`degerine sahip, 0-200mmHg gahsma arallgl igin tasarlanan sensérde, basmg: ile linear
`
`175fF kapasite degigimi gézlenmigtir.
`
`Bu gall§ma mikroi§lenmi$ kapasitif basmg: sensérleri fizerine yapllan ilk
`
`ulusal galismadn'.
`
`Anahtar Kelimeler: Silisyum mikroifieme, kapasitif basmc;
`
`senséirii,
`
`ttimle§tirilmi§ dfizlemsel bobin.
`
`vi
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`Abbott
`Exhibit 1010
`Page 006
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`

`

`
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`ACKNOWLEDGMENTS
`
`I would like to thank Asst. Prof. Dr. Tayfim Akln, my thesis advisor, for all
`
`of his guidance, support, and help for the whoie duration of my graduate study.
`
`I wish also to thank Prof. Dr. Khalil Najafi for providing the fabrication
`
`facilities at the University of Michigan, and Dr. Babak Ziaie for his help during
`
`bonding and testing. Thanks are extended to the technical staff and colleagues at the
`
`University of Michigan for their help during the fabrication of the sensors.
`
`I would
`
`like to acknowledge; ELIMKO for industrial advises, for the development of the
`
`pressure chamber test fixture, and for the preparetion of the PCBS, ASELSAN for
`
`wire-bonding of the samples, and TUBITAK-BlLTEN for project support.
`
`Thanks are also given to my officemates: Haluk Ktilah for many valuable
`
`discussions and frendship, Selim Eminoglu for massive support of computer
`
`hardware and software, Zeynel Olgun for his great efforts on the pressure sensor
`
`readout circuit design, and Deniz Sabuncuoglu Tezcan for creating a nice and
`
`enjoyable office climate.
`
`I would like to thank Nezaket Miilayim for her help,
`
`encouragement, and patience. Lastly, I would like to thank my parents for their
`
`patience, encouragement, and support.
`
`This
`
`research is
`
`a part of
`
`the project
`
`shortly
`
`entitled
`
`as TU-
`
`MECROSYSTEMS sponsored by NATO Scientific Affairs Division in the
`
`framework of the Science for Stability (SfS) Programme. Also it is supported by the
`
`National Science Foundation Internationai Grant, under contracts INT-9602182.
`
`vii
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`Abbott
`Exhibit 1010
`Page 007
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`
`
`TABLE OF CONTENTS
`
`'esearch Objectives and Thesis Organization ................................................. 9
`
`DESIGN-METHODOLOGY FOR CAPACITIVE PRESSURE SENSOR .......... 11
`
`
`
`=
`
`..
`
`=
`.ZINTRO'DUCTIONLI;................................................................................................ 1
`
`
`HistoryofSolid-State Pressure Sensors ........................................................... 3
`
`
`ypesofMicromachlned Pressure Sensors ...................................................... 4
`TWo Pressme Sensor Structures Deveioped1n This Study .............................. 7
`
`
`
`. DiaphragmShapes and Load—Deflection Theory ........................................... 11
`' 2.1.1Planar Diaphragms ........................................................................... 13
`_ 212Non-Planar Diaphragms ................................................................... 18
`" -"2.13 CAD Tools for Design and Simulation ............................................ 21
`2 2'_ InductorStructure........................................................................................... 22
`
`:' -.2.3Des1gn Consideration ..................................................................................... 25
`.924Summary
`.................................................................................................. 26
`
`.2'PRESSUR1: SENSOR FABRICATION ............................................................ 27
`
`3.1 Diaphragm Fabrication Methods.................................................................... 27
`
`.
`
`-.
`
`
`
`3.1.1
`
`Diaphragm Fabrication Based on the Time Dependent Etching ...... 28
`
`' 3.1.2
`
`Highly Boron-Doped Diaphragm Formation ................................... 29
`
`viii
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`Exhibit 1010
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`I._:lassp1ocess....................................................................................38
`
`3-.”2'313"32'3j_';1:Ellectrostatic Bonding ....................................................................... 39
`I'- 4 __11--._l3_issolved Wafer Process.................................................................. 40
`
`v1ty ISceding ................................................................................................ 41
`
`
`11161115161131 .................................................................................................... 42
`
`74.
`.ABRICATION AND TEST RESULTS ........................................................... 43
`
`_es_i_g_111)_fThe Test Sensors ............................................................................ 43
`Fabrlcation Results ......................................................................................... 47
`
`3I Integrated Pianar Coil Measurements ............................................................ 55
`
`
`_ 4111d1v1dua1 Sensor Capacitance Measurements ............................................... 57
`I 5 Sensor Characterization Under Pressure ........................................................ 58
`
`I 1136-: Sensor Reliability ........................................................................................... 63
`
`.. 47 6111161116011...................................................................................................... 64
`
`
`
`SlSchmltt Oscillator and RC Oscillator ............................................................. 66
`:7 _52 ESWitched Capacitor Charge 1integrator ........................................................... 67
`' 5'13 H The Pressure Sensor Readout Circuit Designed in This Study ...................... 68
`:I
`..
`' 54 conclusions .................................................................................................... 72
`
`
`
`_'
`
`'
`
`
`
`
`
`Electrochemwal Etch-Stop Method for Diaphragm formation ........ 3O
`
`
`
`
`'
`..
`
`9
`
`f
`
`.6. CONCLUSIONS AND FUTURE WORK ......................................................... 73
`
`? REFERENCES ..................................................................................................... 75
`
`I
`
`. APPENDIX : Process Sheet for The Capacitive Pressure Sensor ................... 79
`
`ix
`
`
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`Exhibit 1010
`Page 009
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`

`
`
`4.1
`
`The layout of the twelve capacitive pressure sensj
`
`4.2 The layout of the sensor #12 ........... . ..............
`
`4.3 Batch fabricated twelve pressure sensors on a h
`
`
`
`4.4 Closer view of the pressure sensor #8 .......
`
`4.5 Glass substrate for the pressure sensor #8.
`
`
`
`
`4.6 The silicon part of the pressure sensor #8 .....
`4.7 DEKTAK measurements of the cavity depth of V
`
`
`
`4.9 Gold electroplated planar coil structures on thegfi
`
`4.10 SEM photograph of the gold electroplated coil
`
`4,11 Electroplating of coil windings...........
`.
`
`4.12 SEM view of the glass recess and the interco
`
`and the capacitor plate.
`
`4.13 DEKTAK measurements of the cavity depiho
`
`4.14 DEKTAK measurements of the electroplated
`
`
`
`
`4.17 The test setup for the pressure sensor charact
`
`4.18 Picture of the test fixture for the pressure sen
`
`4.19 The PCB-substrate assembly of the pressulfi
`
`4-20 Pressure versus capacitance change test rchl
`
`4-21 Pressure vs. capacitance change tests resul
`
`5-1 A Schmitt—trigger oscillator design..........u
`
`5.2 An RC—oscillator design.
`
`5-3
`5-4
`
`55
`
`4.14 The inductance and the parasitic resistance ch
`4.15 The inductance and the parasitic resistance ch
`4.16 The inductance and the parasitic resistance Ch
`
`
`
`
`
`
`
`.-
`.
`-
`Simplified circuit of a switched capa its
`
`SChematic View and clocking 0f th- '-
`
`readout circuit developed for the fall.
`Layout of the pressure sensor r6440“
`
`Photograph of the fabricated P17?
`5 -6
`
`5-7 Output of the clocking ciI‘CUinyf
`
`5-8
`The circular board with sensOI' 3‘1
`
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`Exhibit 1010
`Page 010
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`

`LIST OF FIGURES
`
`
`
`type capacitive pressure sensor
`
`
`Proiectedworldwide MEMS market and the share of the micromachined
`pressure sensor .................................................................................................. 2
`
`General structure of pressure sensors ............................................................... 5
`
`
`I
`'
`'-Cross-section view of the industrial
`
`I snucture ............................................................................................................ 7
`
`l':--:IB1omedical type capacitive pressure sensor. ..................................................... 8
`'ii Glasspart of the sensor with the planar coil structure placed into the recess... 8
`
`CrOISS—section View of some diaphragm structures. ......................................... 12
`
`
`I
`Iléarallel plate capacitor: .................................................................................... 12
`
`II'I:"I..-'.Ge‘neral diaphragm geometry........................................................................... 13
`
`Top View of one-quarter of a meshed diaphragm. ........................................... 17
`
`
`IThe basic structure for a planar inductor coil. ................................................. 23
`II
`I-
`: .I_Ciicu1t model for the integrated coil................................................................ 23
`
`I:_Time dependent diaphragm fabrication steps. ................................................. 28
`II Boron-doped diaphragm formation steps. ....................................................... 29
`I :I.3I_EtC_11r-ate versus doping density graphic ofboron doped silicon. .................... 29
`Fabrication steps of diaphragm formation using electrochemical etching.
`300
`. Dielectric diaphragm formation steps.............................................................. 31
`I. Cross~section view and the layout ofthe industrial type pressure sensor ....... 34
`
`I
`
`._
`
`I
`
`
`
`
`'_
`
`_ Cross-section view and the 1ayout of the biomedical type pressure sensor ..... 35
`- Silicon wafer process ofthe pressu1e sensois.................................................. 36
`' Glass wafer process for the pressure sensors................................................... 38
`' "3 10 The setup for electrostatic bonding ofthe silicon and glass wafers. ............... 4G
`-.j
`"i 3.31 The pressure sensor structure before and after wafer dissolve process. .......... 40
`3.12 Illustrative picture of cavity sealing on the pressure sensor. ........................... 41
`
`" .-
`"I-
`
`
`5-
`
`x
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`Abbott
`Exhibit 1010
`Page 011
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`

`

`(210561“View. of the pressure sensor #8 ............................................................. 49
`: lass substrate for the pressme sensor #8. ...................................................... 50
`
`
`
`55
`
`62
`
`5.3 The circular board with sensor and readout circuitry combined on it. ............ 72
`
`xi
`
`
`
`..
`
`'
`
`'
`
`.I __I Pressure versus capacitance change test result of the sensor #i .....................
`
`
`
`.
`.313 view of the giass recess and the interconnect metal between the coil
`andgthe'fcapacitor plate. .................................................................................... 54
`
`DE'KTAKimeasurements of the cavity depth of the glass wafer.
`S4
`
`' DEKTAK measurements of the electroplated bonding pad height.
`
`I Theinductance and the parasitic resistance change of the coil #9. ................. 55
`
`
`I Thefinductance and the parasitic resistance change of the coil #10.
`56
`Thei'nductance and the parasitic resistance change ofthe coil #11. ............... 56
`
`
`- Thetest setup for the pressure sensor characterization.................................... 58
`_ Fictuieofthe test fixture for the pressure sensors characterization................. 59
`
`;.- The PCB-substrate assembly of the pressure sensor. ...................................... 59
`61
`
`66
`....................... 67
`-: AnRC~oscillator design.
`
`ISirI'iplified circuit ofa switched capacitor charge ingetrator technique. . . . . ....68
`=
`I L:
`II '1' -'-:Schematic view and clocking of the switched capacitor charge injection
`
`ilireadout circuit developed for the fabricated pressure sensor in this study. .....69
`'-
`IL-ayout ofthe pressure sensor readout circuit. ................................................. 7G
`
`5 _'
`'Photograph of the fabricated pressure sensor readout electronic circuit.
`70
`
`Output of the clocking circuitry....................................................................... 71
`
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`Exhibit 1010
`Page 012
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` 47
`
`
`C'apautan'ce ofthé' fabficfiidd capacitive pressure sensors.
`
`................. 58
`
`xii
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`Exhibit 1010
`Page 013
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`
`
`CHAPTER I
`
`INTRODUCTION
`
`Pressure is one of the most commonly needed measurements in control
`
`systems. Therefore, the pressure transducer is one of the most widely used physicai
`
`transducer that converts mechanical signals into electrical signals. For instance, in
`
`the automotive industry, pressure sensors are used to measure oil, fuel, and intake
`
`manifold pressures for real time electronic engine control.
`
`In the manufacturing
`
`industry, the pressure sensor is one of the key components required for process
`
`automation.
`
`In the biomedical field, the pressure sensor is used to monitor the
`
`pressure in the cardiovascular and respiratory systems. All these applications have
`
`some strict requirements. Most important requirements are low cost, small size, and
`
`high accuracy. In addition, depending on the applications, there are other demanding
`
`requirements, like extended operation range and integration with the readout signal
`
`processing circuitry.
`
`The development of Micro-Electro-Mechanical Systems (MEMS) technology
`
`gives us
`
`the opportunity to produce solid—state pressure sensors
`
`that meet
`
`requirements listed above. Silicon micromachining techniques are the key methods
`
`of the MEMS technology, capable of providing solid-state pressure sensors easily at
`
`low cost and in small size. Silicon micromachining is, in the most common usage, a
`
`chemical etching process for silicon wafers to manufacture three-dimensional
`
`microstructures.
`
`This technology is consistent with semiconductor processing
`
`techniques including
`
`photolithography,
`
`thin-film deposition, and chemical and
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`Abbott
`Exhibit 1010
`Page 014
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`

`
`
`
`ss sciated readout circuitry can be built on the same silicon wafer, integrated
`.the
`
`ith'-i'tfiei_'transducer, creating the term “smart sensors” [2], and a great amount of
`
`research-ems been devoted to the implementation and improvement of “smart
`
`:ssfissrg’zgpi MEMS devices.
`
`
`_The micromachined pressure sensor market shows rapid growth throughout
`
`the world due to these advantages and the development in the fabrication technology.
`
`.
`_2 The 'iiiicromachined pressure sensor is the first semiconductor sensor product in the
`
`JI:_S§i1-S-$£Iih1ark6ts and today, it is stiil dominating the MEMS market. Figure 1.1 shows
`
`thegrow of the MEMS market and the expected market
`share of the
`
`iiiiimiCromachined pressure sensors in the year 2000 [3}. Pressure sensors are the
`
`leading product in the market, and wili have a 25% share in the $4 biliion expected
`
`I
`; MEMS market in the year 2000.
`
`
`Market Segment
`in 2000
`
`-
`
`1993
`
`1994
`
`19:95
`
`199?
`1996
`Year
`
`1998
`
`1999
`
`2000
`
`Figure 1.1: Progected worldwide MEMS market and the share of the
`micromachined pressure sensors [3].
`
`H
`
`1:2
`
`10
`
`Regalia"
`amcantrnl
`19%
`
`3 g
`
`E
`i
`N 6
`
`so
`
`
`
`Abbott
`Exhibit 1010
`Page 015
`
`

`

`
`
`
`
`silicon
`study on the development of
`first
`the
`reports
`1115;111:3311
`1i omachmed capacitive pressure sensors in Turkey. Two types of pressure sensors
`
`deveioped one- of them is for industrial control systems, while the other15 for
`romed1calapplications as an implantable pressure sensor. Section 1.1 overviews the
`
`historyof-the solid-state p1essure sensors. Section 1.2 describes the two main types
`
`rciomachined pressure sensors, i..e, piezoresistive and capacitive sensor, and it
`lrststheir advantages and disadvantages over each othe1. Then, Section 1.3
`is
`
`
`.__des'¢fib¢ niche.two pressure sensor structures developed in this study for industrial
`
`
`
`I olsyjst'eins and for biomedical applications. Finally, Section 1.4 summarizes the
`:objective'and the organization of the thesis.
`
`H1story of Solid-State Pressure Sensors
`
`
`
`
`started with the use of
`{The miniaturization of pressure sensors has
`
`__sem1condiictors1n the late 1940’s. Silicon bars were cut out of a wafer to form
`
`resisnve strain gages, and these bars were adhesively bonded onto a metal diaphragm
`
`
`. wluch'ex'posed to media. The applied pressure to this diaphragm was deflecting the
`diaphragm, and the stress induced in the diaphragm transmitted to the bonded strain
`gages The resistance change on the gages was proportional to the applied forces
`
`
`First'mdustnal types of these transducers were used1n 1958. However, these devices
`;;-'1111d_s¢111e problems, like low yield, poor stability, and thermal mismatch of the glued
`
`.. 1s1l1co11 011 the metal
`
`
`
`
`I
`
`:":-'.The performance of the pressure sensors was improved in 1960’s by
`
`[implementing the strain gages in silicon diaphragms. This technique also reduced
`
`__ the-:size of the sensor. The diaphragm formation from a bulk material was achieved
`
`I - ..- "fiibyiinechanical milling and chemical etching processes. But, the cavity formation was
`
`
`-
`
`done in one—at-a—time mode, which increased the cost.
`
`
`
`Abbott
`Exhibit 1010
`Page 016
`
`

`

`
`
`By using anisotropic etchants for batch fabrication in 1970’s improved the
`
`diaphragm formation. Batch processes performed on an entire wafer, so that
`hundreds of sensor diaphragms were made simultaneously. This has also reduced the
`
`size and manufacturing cost, improved sensor stability, lowered temperature errors,
`
`and caused more accurate electrical parameters. These sensors have begun to be used
`
`in aerospace and industrial-control areas.
`
`in 1980‘s, the progress in the integrated circuit technology has also helped to
`
`mature silicon micromachining techniques and to expend the applications of MEMS
`
`technologies, making it possible to implement microsensors with extensively reduced
`
`size, lover cost, and higher performance. Therefore, the use of micromachined
`
`sensors have an exponential increase, expected to reach a $14 billion market in the
`
`year 2000. Silicon micromachined pressure sensors are expected to have a 25%
`
`share in this MEMS market.
`
`1.2 Types of Micromachined Pressure Sensors
`
`There are two types of solid-state pressure sensors that are widely used:
`
`piezoresistive {4,5,6] and capacitive [7,8,9]. Figure 1.2 shows general structures of
`
`piezoresistive and capacitive pressure sensors, where both have a thin diaphragm that
`
`deflects with applied pressure difference.
`
`Piezoresistive sensors use resistors built into the diaphragm as the sensing
`
`elements. The diaphragm deflects whenever a pressure is applied. The stress
`
`induced by the bending diaphragm causes a change in resistance of these resistors
`
`due to the piezoresistive effect. The electrical output for this type of pressure sensor
`
`is usually in the form of a voltage output of the resistive network on the diaphragm.
`
`For a capacitive sensor, the device is made of a suspended diaphragm and a fixed
`
`reference plate,
`
`forming a parallel plate capacitor.
`
`The suspended diaphragm
`
`undergoes elastic deformation when subjected to a differential pressure. Therefore,
`
`the distance between the diaphragm and the reference plate changes, causing a
`
`Abbott
`Exhibit 1010
`Page 017
`
`

`

`
`
`
`ance- change in the pressure sensor. The electrical output is the efi‘ective
`
`1t --
`(":3between the reference plate and the deflected diaphragm.
`
`
`Piezoresistors
`
`
`
`
`
`' Diaphragm
`
`Rim
`
`Fixed Capacitor Plate
`
`(19}
`
`
`Figure" 1.2: General structure of pressure sensors: (a) Piezoresistive
`type, (b) Capacitive type.
`
`
`
`and
`advantages
`sensors have
`and capacitive pressure
`Pieaoresistive
`
`
`_isa_ ___antages over each other. Piezoresistive pressure sensors are easier to fabricate
`
`With respect to capacitive counterparts. They show linear response in a large span of
`
`"1313333113? Change, and this change can be converted to electrical signal easily without
`anY”«"44"(fig-11mg:'ation due to their low output resistance. However, diaphragm can not be
`
`'5' i¢§t§§h610vv a certain thickness due to the piezoresistive material piaced in the
`
`'-d1aphmgm,”causir1g lower pressure sensitivity Temperature sensitivity is another
`
`' majorconcern for piezoresistive sensor since the resistance of the resistors in the
`
`
`dlathgmIS temperature dependent. Therefore, piezoresistive types of sensors often
`
`
`
`Abbott
`Exhibit 1010
`Page 018
`
`

`

`
`
`= the readout circuitry, since the sensing part is piezoresistive material diffused into the
`
`diaphragm and the resistance changes directly with the applied pressure. The
`
`_ -_addttion"capacit1ve p1essure sensor shows higher performance if high sensitivity,
`
`10 spanof pressure change, and time stability are taken into consideration
`
`
`Both piezoresistive and capacitive sensor structures require a readout
`
`electronic circuit. For piezoresistive type, the sensor itself is automatically construct
`
`
`common __readout configuration for this type of sensors is the Wheaston bridge
`
`configuratlon However, a compensation circuit may be required due to high
`temperature. dependency and nonnlinearity at high-pressure ranges. Resistive bridges
`
`
`
`
`requne considerable supply currents, which are not tolerable for catheter-tip devices
`
`
`for readout and packaging.
`
`.For the capacitive sensor, a separate readout circuit is highly required, since
`
`
`eléegacitance change can be as low as few femto-farads, and the electrical lead
`§5hiiection for measurement causes parasitic capacitance over initial sensor capacitor
`
`
`dueto small size of the structure. This problem can be solved with the attachment of
`an electronic circuitry next to the sensor, which gives an output voltage chance with
`
`
`
`respect to capacitance change meaning pressure change.
`
`
`
`Abbott
`Exhibit 1010
`Page 019
`
`

`

`
`
`
`wail-’ressure Sensor Structures Developed in This Study
`
`
`
`-F1gure':l.3 shows a cross-sectional view of the industrial type capacitive
`pgesglfl'
`'Isensorustructure designed in this study. The sensor consists of two parallel
`apacito'rsi'I' one of them is the pressure sensitive capacitor and the other is the
`fixed=:reference capacitor. The pressure sensitive capacitor is formed by a thin silicon
`
`
`
`" land a- fixed bottom plate. Whenever pressure is applied ever the sensor,
`thinisihcon diaphragm deflects downwards and gets closer to the bottom plate,
`
`more urg'the value ofthe variable capacitor. By measuring the capacitance, pressure
`
`bei'nie'afsured, since the amount of deflection of the diaphragm is proportional to
`the applied pressure. The reference capacitor has a thicker diaphragm that does not
`
`
`
`d__
`ect,_.:a'nd. it is used as a reference capacitance for the readout electronics. The
`
`
`ca: :aciito'rs are constructed in two parts: (I) the siiicon part that forms the diaphragms
`
`and-.;supporting rims, defined by high boron doping of silicon, and (2) locally
`
`metallized glass part which forms the fixed plate of the capacitors and support
`
`electrical connections thrOugh metal lines.
`
`
`
`
`"'7- Pressure Sensitive Capacitor
`
`Reference Capacitor
`
`
`
`- Figure 1.3: Cross-section view of the industrial type capacitive pressure
`sensor structure.
`
`
`
`
`
`
`
`The second pressure sensor developed in this study is a new sensor structure
`.
`for biomedical applications. The sensor can be placed in a body or blood vessels, and
`.
`3: llows to measure the pressure remotely, without a need for wire connection
`
`Flgure 1.4a shows the cross-section view of this new implantable wireless pressure
`
`Elli-9? structure. The general sensor structure is same as the previously explained
`
`
`lildUStl‘ial type pressure sensor. However, in this type, there is only one capacitor,
`
`Abbott
`Exhibit 1010
`Page 020
`
`

`

`In addition, a planar coil structure placed into the recess
`which is pressure sensitive.
`on the glass using electroplating as shown in Figure 1.5. This coil integration with the
`sensor capacitor forms an LC resonant circuit as shown in Figure 1.4b. The change in
`the resonance frequency due to capacitance change is sensed remotely with inductive
`coupling, eliminating the need for wire connection.
`
`Pressure Sensitive Capacitor
`
`
`
`Planar Inductor
`
`Glass Recess
`
`(a)
`
`(b)
`
`(a) Cross-
`type capacitive pressure sensor:
`Figure 1.4: Biomedical
`section View of implantable wireless pressure sensor,
`(b)
`Electrical equivalent of the sensor. The change in the resonance
`fi'equency due to capacitance change is sensed remoteiy with
`inductive coupling, eliminating the need for wire connection.
`
`
`
`Planar Inductor
`
`Fixed Capacitor Piate
`
`Glass Recess
`
`
`
`
`Figure 1.5: Giass part of the sensor with the planar coil structure placed
`into the recess
`
`Abbott
`Exhibit 1010
`Page 021
`
`

`

`ResearchObj'ee'tiv'esigaind' Thesis Organization
`
`fabricateri at the same time using batch-compatible dissolved—wafer process.
`
`
`'iiiedié-Ito.de51gnand fabricate miniature micromachined capacitive
`
`sensors forrndustrial and biomedical applications. The specific objectives
`
`.be summarized asi'follows:
`
`
`
`D'esinging capacitive pressure sensors working in different pressure ranges
`
`.both'ifor "control systems and biomedical applications. Twelve capacitive
`
`
`pressure sensors have been designed working in six different operation ranges.
`
`Maskfsa for sensor fabrication has been drawn and twelve sensors have been
`
`
`
`Integration of a coil structure with the capacitive pressure sensor to deveiop
`
`wireless sensor for biomedicai applications. Pianar rectangular coil structure
`
`' has been integrated with the sensor capacitor inside the sensor body to form
`
`air-LC circuit for remotely pressure measurement by scanning resonace
`
`frequency of the devise.
`
`
`-I'I_’£)eVeiopment of a measurement setup for detailed characterization of the
`
`pressure sensors. A pressure chamber has been: designed to test the sensors
`
`
`
`ffThe study has started by learning and comparing various different structures
`the can be used to implement a pressure sensor for process control and biomedical
`
`'fl_§6.3_ Designed pressure sensors have been fabricated using the facilities of the
`Uiiiv'ersity of Michigan. A test setup has been prepared for characterization of the
`
`Sensors, and mean While electronic readout circuit for the sensors have been designed
`
`under pressure.
`
`
`
`and fabricated in the Semiconductor Laboratories at TUBiTAK Marmara Research
`
`center.
`
`
`
`Abbott
`Exhibit 1010
`Page 022
`
`

`

`
`apf