IC Process technology

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1 Lecture 6 Designs of MEMS /NEMS 1 清華大學材料科學與工程系廖建能教授

2 MEMS/NEMS Design Ideas Functionality, applications, problems/limitations, Micro/Nano-scale operation principles Physical, chemical and biological models, material properties, scaling effect, Analysis and modeling of devices and systems Packaging and integration NTHU, Chien-Neng Liao

3 Energy Transformation Thermal expansion, T-dependent phase transformation, Thermal Thermoelectric, Joule heating, thermal resistive, Mechanical Piezoelectric, piezoresistive, Electrical NTHU, Chien-Neng Liao 3

Thermal Actuators Thermal energy transformed into mechanical movement Once applying a current, the narrow beam will be heated up more and expand

4 Thermal Actuators Thermal energy transformed into mechanical movement Once applying a current, the narrow beam will be heated up more and expand more due to higher resistance and current density. Once stopping current input, the structure will come back to original position NTHU, Chien-Neng Liao 4

5 Thermal Actuators pad Poly wire pit Poly wire A A beam Metal 1 beam Thermally driven cantilever beam Thermal expansion mismatch induced actuation Thermal resistive heating (poly wire) to change the temperature of the beam Electrical Thermal Mechanical NTHU, Chien-Neng Liao 5

6 Shape Memory Alloys Medical - Microsurgical instruments, stents, artificial muscle Aerospace - Connectors, lock rings Automotive - Ni-Ti thermostat Industrial - Valves, pipe connectors Consumer - Eyeglass frames Safety - Fire safety valves SMA valve open and release hot water at the proper temperature NiTi surgical tools: Precise bending of the tool to the proper shape in micro-surgery NTHU, Chien-Neng Liao 6

7 Piezoelectric Actuator Piezo. Mat. Piezo. Mat. Piezoelectric stack actuator Piezoelectric bimorph actuator NTHU, Chien-Neng Liao 7

8 Inchworm stepping motors Movement along a rod by 3 piezoelements Unlimited movement Good resolution Maximum speed mm/s Drawbacks - Expensive - Small lateral load NTHU, Chien-Neng Liao 8

9 Piezoresistive AFM NTHU, Chien-Neng Liao 9

10 Electromagnetic Actuator NTHU, Chien-Neng Liao 10

11 Thermoelectric Coolers Laser cooling modules Telcom cooling module Multi-stage module Fiber optics cooling modules NTHU, Chien-Neng Liao 11

12 Thermoelectric Sensor Thermal sensors IR detectors NTHU, Chien-Neng Liao 1

convection Al/poly-Si thermopiles measure changes of

13 Thermoelectric accelerometer Poly-Si heating wire suspended across a cavity Heat transfer by natural convection Al/poly-Si thermopiles measure changes of thermal profile caused by acceleration NTHU, Chien-Neng Liao 13

Piezoresistive Pressure Sensors Measures material stresses Resistors normally arranged in a Wheatstone bridge to cancel TCR effect Sensitivity of piezoresistors decreases as

14 Piezoresistive Pressure Sensors Measures material stresses Resistors normally arranged in a Wheatstone bridge to cancel TCR effect Sensitivity of piezoresistors decreases as temperature increases Nonlinearity of response to applied pressure depends upon the location of resistors in the strain field and the deflection of membrane NTHU, Chien-Neng Liao 14

Capacitive Pressure Sensor Measures average deflection The change of capacitance is not linear with respect to deformation or pressure (but the relationship is reproducible)

15 Capacitive Pressure Sensor Measures average deflection The change of capacitance is not linear with respect to deformation or pressure (but the relationship is reproducible) Disadvantage: small capacitance (generally pf) > measurement circuit has to be integrated on the chip or specially designed to null the stray capacitance NTHU, Chien-Neng Liao 15

16 Actuator/Sensor design considerations Operational principle Process feasibility Responsibility (output signal/input physical quantity) Sensitivity (signal to noise ratio) Output force/energy/power Frequency response Dynamic range Limitations: Q factor, Failure mode Temperature (or other factors) dependency Reliability Integration and packaging NTHU, Chien-Neng Liao 16

17 Operation principles and materials properties Examples: Electrostatic capacitor Solenoid inductor Shape Memory Alloy Thermoelectric effect Piezoelectric effect Thermal expansion and thermoresistive NTHU, Chien-Neng Liao 17

18 Electrostatic Forces Capacitance: CQ/Vε o ε r A/d ε x10-1 F/m ε r : dielectric constant Stored energy W W e e V Vdq CVdV V A ε d 1 CV NTHU, Chien-Neng Liao ε r V ε ( Ad ) Stored energy density 1 ρ ρ W 1 e ' εe D E E

19 Electrostatic Force Perpendicular motion F W e e Lateral motion independent on y NTHU, Chien-Neng Liao 19

20 Principle of Electrostatic Actuator Dielectric slab Conductor slab NTHU, Chien-Neng Liao 0

21 Electrostatic Actuation NTHU, Chien-Neng Liao 1

IA Stored energy: I di Wm 0 dt 1 N B μ ( ) ( Al) l μ ( N / l) W m W

22 Solenoid inductor emf di L dt Ampere s law ρ H dl ρ Φ NI N BA μ HA dφ dt N μ l Inductance of solenoid L μn l A Stored energy density: IA Stored energy: I di Wm 0 dt 1 N B μ ( ) ( Al) l μ ( N / l) W m W m ( emf ) dq L( ) dq B 1 ' μ ρ ρ H B LI NTHU, Chien-Neng Liao 1 B ( Al) μ

23 Magnetic Force Translational motion F m W m 1 W m LI 1 dw m n I 1 μn AlI A[ μ ( l dy) + μ dy] nn/l 0 B μ F m dy l μ μ 0 (1 + χ) μ: permeability χ: susceptibility μ 0 Magnetic restoring force F m dw dy m 1 n I Aμ 0 χ NTHU, Chien-Neng Liao 3

24 Theory of Shape Memory Alloys (SMA) Reversible thermal-mechanical transformation of the atomic structure of the metal at certain temperatures Austenite form high temperature shape - Alloy above transformation temperature - Alloy returns to a desired shape (after deformation at martensite form) and generates force/stress and a displacement Martensite form low temperature form - Alloy below transformation temperature - Remains in austenite form position if there is no external stress - Alloy can be deformed with an external stress NTHU, Chien-Neng Liao 4

25 SMA Operation Principle NTHU, Chien-Neng Liao 5

26 SMA operation principle Temperature rises, Mart. Aust. form - length decreases Temperature falls, Aust. Mart. form - length increases (if external force present) Transformation hysteresis exists NTHU, Chien-Neng Liao 6

Shape Memory Alloy (SMA) Heating of SMA by electric current fed

), also additional cooling possible Maximum deformation 8%, usually

4% Several alloys with different properties - Ni-Ti alloy most

27 Shape Memory Alloy (SMA) Heating of SMA by electric current fed through the element Cooling with ambient material air, water, etc.), also additional cooling possible Maximum deformation 8%, usually approx. 4% Several alloys with different properties - Ni-Ti alloy most common - Also Au, Cd, Cu alloys - Alloy composition affects transformation temperatures, hysteresis, maximum force, NTHU, Chien-Neng Liao 7

28 SMA Actuator Advantages - High force/weight and force/volume ratios - Large deformation - Heating by current fed through the alloy > simple - Cooling by ambient material > simple - Raw material inexpensive Disadvantages - One way operation > bias force required - Heating/cooling cycles reduce band-width - Amount of cycles reduces maximal deformation (>10 5 cycles > maximal deformation 4%) - Cycling changes the properties of the alloy - Hysteresis (10 30 C), nonlinearity NTHU, Chien-Neng Liao 8

29 Energy density for different energy forms B /μ 0 NTHU, Chien-Neng Liao 9

30 Thermoelectric effect: Seebeck A S AB S A -S V B (ΔV/ΔT) Je0 Known as Thermocouple T 84.5% Ni, 14.% Cr, 1.4% Si B A T+ΔT Measuring junction, T M 95% Ni, % Mn, % Al, 1% Si Alumel ΔV ΔT K type TC Reference junction, T 0 NTHU, Chien-Neng Liao 30

31 Thermoelectric effect: Peltier Heat absorption J Q A A Heat generation B Electric current direction A thermodynamically reversible process A measure of entropy change when carrier across the junction Peltier coefficient is defined π AB J Q /J E J E J Q NTHU, Chien-Neng Liao 31

32 Thermoelectric Operation principle T H Heat flux T C p n Electric current flux p n T C + - Load R L - T H I-Source + Generator Refrigerator NTHU, Chien-Neng Liao 3

33 Thermoelectric Generation Efficiency η W/Q S W I R L Q S ST H I + K(T H -T C ) - I r / I S(T H -T C )/(R L +r) T H Peltier heat extraction Heat conduction Joule s heating p n η opt ( T H T T H C ) T S Z Kr C ( 1 + ZT T H S σ λ ' ) 1 + ( 1 + ZT ' ) 1 ZT η opt T C Load R L NTHU, Chien-Neng Liao 33

34 Thermoelectric Refrigeration Efficiency φ q c /W W S (T H -T)I+ I r q c STI - K(T H -T) - I r / Peltier heat extraction φ opt Heat conduction ' T [( 1 + ZT ) T ) [( 1 + ZT 1 ' ( TH ( T T ) H max ) 1 ZT Joule s heating T M H + 1] Electric current T ] T H ZT φ opt πisti K(T H -T) (I r)/ NTHU, Chien-Neng Liao 34 T n

35 Requirements of good TE materials High figure of merit Z (S σ/λ) Both η and φ increase with (1+ZT) 1/ High Seebeck coefficient S High Electrical conductivity σ Low Thermal conductivity λ NTHU, Chien-Neng Liao 35

36 Piezoelectric effect A force deforms an crystal and forms an electric dipole by displacing the distance between positive and negative charge center Conversely, the application of an electric field to a piezoelectric crystal leads to a physical deformation NTHU, Chien-Neng Liao 36

37 Piezoelectric effect Direct effect D i d ik σ k + ε(d) ik E i Inverse effect ε k d ik E i +(S ik ) E σ k i 1,,3 indices of components of polarization k 1 6 of mechanical stress and strain D i is electric displacement vector [3x1], C/m E i is the electric field vector [3x1], V/m σ i is stress (force/unit area) tensor [6x1], N/m ε k is strain (relative displacement) tensor [6x1] d ik is a matrix of piezoelectric constants [3x6], m/v ε(d) ik is the permittivity measured at constant stress [3x3], As/Vm S E is the elastic compliance matrix when subjected to a constant electric field [6x6], m /N NTHU, Chien-Neng Liao 37

38 Piezoelectric effect NTHU, Chien-Neng Liao 38

39 Piezoelectric effect NTHU, Chien-Neng Liao 39

40 Piezoelectric Materials NTHU, Chien-Neng Liao 40

41 Thermal Expansion Effect Thermal expansion mismatch causes stresses in bonded layers and thin films NTHU, Chien-Neng Liao 41

42 Thermoresistive Effect Applications: heating wire or temperature sensors NTHU, Chien-Neng Liao 4

43 Scaling effect The change of dominant physical quantities between different scales is called scaling effect gravitational, inertial forces become less effective van der Waals forces, electrostatic forces, surface tension forces become more important NTHU, Chien-Neng Liao 43

44 Scaling of 3D Objects Surface area A~L Volume V~L 3 Mass (weight) mρv~l 3 Moment of inertia ImR ~L 5 Torque τ(ma)r~l 4 NTHU, Chien-Neng Liao 44

45 Scaling effect Resonance frequency f 0 ~ L -1 Electrostatic force: Perpendicular motion Lateral motion F e F e dw dx dw dy e e 1 A ε V x 1 z ε V d F is independent of scale, F ~ V L 0 NTHU, Chien-Neng Liao 45

46 Electrostatic force EA Q ε σq/a σ L ε gρl 3 NTHU, Chien-Neng Liao 46

47 Scaling effect on thermal conduction Phonon transport impacted by material size NTHU, Chien-Neng Liao 47

48 Electrical/Mechanical Systems displacement x charge q force F voltage V velocity dx/dt current I(dq/dt) mass m inductance L spring K capacitance 1/C damping b resistance R NTHU, Chien-Neng Liao 48

49 NTHU, Chien-Neng Liao 49 Model of electrostatic actuator -port capacitor Fixed plate moveable plate z g + - V I + - V + - F W(Q,g) C dg/dt A g Q CV Q W ε 1 ) ( A Q g g Q W F Q ε ), ( C Q A Qg Q g Q W V g ε ), (

50 Electrostatic actuator-charge control + V - I g fixed plate spring k z dg/dt dz/dt g V Q F ε A kz g0 z g0 Qg εa Q( g Q εak Q εak εa 0 ) I + V - W(Q,g) C + - F 1/k When QQ 0, g 0 Q 0 εa kg 0 NTHU, Chien-Neng Liao 50

51 Electrostatic actuator-voltage control I dg/dt dz/dt co-energy W*(V,g) V + V - W*(V,g) C + - F 1/k W*(V,g)QV-W(Q,g) dw*(v,g)qdv-fdg W F * ( V, g) W V εa εav QdV VdV 0 g g ( V, g) εav * * in W ( V, g) εa Q V in g g V g V g in g g0 z g0 εav kg NTHU, Chien-Neng Liao 51

52 Pull-in of electrostatic actuator g F net g 0 z g 0 εav kg in V in g g positive feedback When V > V PI, system lose equilibrium AV ε + k( g0 g) F>0 in the direction of increasing g g δf net F g net δg εav δ F net ( k) δg 3 g V when δg>0, the system becomes unstable if δf net > 0 the system becomes stable if δf net < 0 k εav 3 g > for a stable equilibrium NTHU, Chien-Neng Liao 5

53 Pull-in conditions g F net k gpi εav 3 g εav g PI 3 PI g 3 Equilibrium condition 4 v 7 (1 ζ ) 0 ζ k v 0 V PI V V PI F net ζ kg εav F net + k( g0 g) g PI PI 3 8kg0 7εA 1 g g 0 + k( g0 g ) 0 0 Two equilibrium points merge when ζ1/3 and v1 v0.8 NTHU, Chien-Neng Liao 53

54 Model of electrostatic actuator Electrical domain, I 1 R ( V in Qg ) εa Mechanical domain, F + dg d dg ( g g0 ) b( ) + m ( ) + dt dt dt 1/ k 0 displacement g charge q force F voltage V velocity dg/dt current I(dq/dt) mass m inductance L spring K capacitance 1/C damping b resistance R NTHU, Chien-Neng Liao 54

55 Model of electrostatic actuator V F Z Z T EB MO EM V I F U V U U 0 I 0 I 0 Z T EB ME T Z EM MO I U Blocked electrical impedance + V - Open-circuit mechanical impedance I Linear -port element Open-circuit electromechanical transduction impedance U + - F Z ME F I U 0 Blocked mechanical-electro transduction impedance NTHU, Chien-Neng Liao 55

56 Dynamics of electromechanical systems NTHU, Chien-Neng Liao 56

57 Analogy of Electrical/Mechanical Resonators mass m inductance L spring K capacitance 1/C damping b resistance R NTHU, Chien-Neng Liao 57

58 Mechanical resonator under damping Frequency and phase shift Energy dissipation NTHU, Chien-Neng Liao 58

59 Quality Factor (Q value) Definition: ratio of stored energy and lost energy in one cycle Q E π π τ τω0 ΔE T Mechanical system: Electrical system: E E 0 e t τ δt t τ δe E0e τ m Q τω 0 ω0 b Q L τω ω0 R 0 1 R T E τ km b L C NTHU, Chien-Neng Liao 59

60 Analogy of electrical/mechanical resonators Mechanical Resonator Electrical Resonator NTHU, Chien-Neng Liao 60

cantilever beam change with beam mass Abadal et al,

61 Nano-cantilever Mass Sensor Cantilever beam driven by neighboring electro-plate Resonance frequency of the cantilever beam change with beam mass Abadal et al, Nanotechnology 1 (001) NTHU, Chien-Neng Liao 61

62 Nano-cantilever Mass Sensor Resonance freq. Spring constant k Mass sensitivity: 6.5x10-18 g/hz for 0 μm beam length NTHU, Chien-Neng Liao 6

63 Microelectronics vs MEMS packaging Microelectronic packaging: - weakly dependent on chip functionality - tested at wafer-level - achievable packaging standard MEMS packaging: - strongly dependent on device functionality - tested at die-level or post packaging - difficult to achieve packaging standard NTHU, Chien-Neng Liao 63

64 Integrated vs multi-device hybrids System partitioning - Monolithic device or ASIC+MEMS hybrid Decision making - process flexibility - system size - interconnect reliability - die yield - device performance - cost NTHU, Chien-Neng Liao 64

65 System interface/specifications Signal receiving and response - signal forms: thermal, electrical, mechanical, - environmental issues: temperature, pressure, stress, parasitic effect, biocompatibility, Design specifications - performance over operating temperature range, environment conditions - number and location of electrical connections - device reliability NTHU, Chien-Neng Liao 65

66 Motorola pressure sensor Bulk micromachined Si diaphragms sensed with piezoresistance An absolute pressure sensor requires a backplate to seal the space beneath the diaphragm under vacuum NTHU, Chien-Neng Liao 66

60C-6-20160802091614

60C-6-20160802091614 推薦序防災是全球未來的必須面對的首要工作, 台灣值在這方面進步非常快, 可說在世界上居於領先國家之一, 其中有一項技術, 就是防災的監測我們的團隊, 利用國科會計畫, 在民國 89 年研發出台灣第一座土石流監測與預報系統, 當初