Ferroelectrics. Spartak Gevorgian. Department of Microtechnology and Nanoscience Chalmers University of Technology Gothenburg, Sweden

Transcription

1 Ferroelectrics Material Properties, Processing, and Microwave Applications Spartak Gevorgian Department of Microtechnology and Nanoscience Chalmers University of Technology Gothenburg, Sweden Norwegian IEEE MTT/AP Chapter SINTEF, Trondheim, March, 2006

2 Outline Introduction Materials (Bulk, Thick and thin Film) Devices and Circuit Applications Concluding Remarks: Problems and Perspectives

3 What is this about? Wired Communication New York 1921

4 Wireless Communication Gothenburg, Sweden 2001

5 Electronics DNA: Search for components with enhanced performances

6 Ferroelectrics: Multifunctional Dielectrics Electrode Dielectric with electric field dependent permttivity Electrode Electrode Electrode

7 Ferroelectric Compositions Considered for Microwave Applications ABO 3 Perovskites: Ca x Sr 1-x TiO 3 K x Li 1-x TaO 3 K x Na 1-x NbO 3 Pb x Zr 1-x TiO3 Ba x Sr 1-x TiO 3 x=0-1 Ferroelectric (polar) and paraelectric phases

8 Polarization of Paraelectric Perovskites Nonlinear polarization A B P O E E Field dependent permittivity ε T = ε ( 0 ) ε ( ε ( 0 ) E ) E

9 Ba x Sr 1-x TiO 3 (BST) at Room Temperature x= Dielectric constant, ε b) Temperature, K Smolensky & Isupov (1954)

10 Ba 0.8 Sr 0.2 TiO 3 +MgO. MgO: 0-10% From Doping to Composite Permittivity % 4% 2% Composite 1.5% Doping 1% 0.5% 0% Temperature, C Su & Button (2004)

11 Ferroelectrics- Features Attractive for Microwave Applications-1 Dielectric properties: Permittivity ε ( ) - small size devices: Size ~1/ ε Electric field dependent - tuneable and nonlinear devices Loss tangent tanδ- typically Tuning speed- < 1.0 ns

12 Ferroelectrics- Features Attractive for Microwave Applications-2 Electrical properties: Resistivity- Leakage currents- Breakedown field- Metalic conductivity- Bandgap- Mobility- undoped > Ohm cm extremely low > kv/cm if highly doped (transparent electrode) Eg>3.0 ev 2D electron gas at low temperature-15000cm 2 /Vs

13 Ferroelectric Material Technologies Considered for Microwave Device Fabrication Bulk- single crystal and ceramics Thick film- HTCC, LTCC Thin film- single crystal polycrystalline

14 Bulk Single Crystal (SrTiO3)

15 Four Pole Tuneable Bandpass Filter Based on SrTiO 3 Discs Duroid SrTiO 3 disk resonator SrTiO 3 disks Diameter: 7.0 mm Thickness: 0.5 mm Plates: Cu/Ti Deleniv et. al. Proc. EuMC 2002

16 Four Pole Tuneable Bandpass Filter Based on SrTiO 3 Discs V 300 V 500 V 0 Transmission coefficient, S21 (db) Reflection coefficient, S21 (db) V 500 V -70 T=77K T=77K 300 V Frequency, GHz Frequency, GHz 3 db bandwidth-2.0%;tuneability-8%; Losses-4.0 db Deleniv et. al. Proc. EuMC 2002

17 Bulk Ceramic Ba x Sr 1-x TiO 3 (Project MELODY)

18 Beam Steering Lens Tageman et. al. Proc. EuMC 2005

19 Tuneable Chip Components: Resonators Capacitors and Delay Lines Pd BST68/32 / MgO 60mol% 6 layers Pd/Ag 1,51 mm 9,22 mm

20 LTCC and HTCC Ba x Sr 1-x TiO 3 (Project MELODY)

21 HTCC Phase Shifters in Project MELODY

22 LTCC OBJECTIVES Development of tunable ferroelectric LTCC compositions Sintering temperature: <950 o C ε= ; tanδ < 0.01 at 2-50 GHz; Tunability >10% Development of processing routes for single and multilayer ferroelectric films with: Thickness 5-50 μm; Area 100x100 mm 2 Development of fabrication routes for electrodes

23 LTCC BSTO Performance 210 Extracted dielectric permittivity, ε r No bias 2V/μm 4V/μm Frequency, GHz tanδ f; (~0.12@25GHz)

24 LTCC Phase Shifters in Project MELODY ~1.5mm TEMEX

25 Measured Phase LTCC Shifter Performance Matching S11, db No bias Frequency, GHz 1.25V/μm 2.4V/μm 4V/μm Phase shift Δφ, deg V/μm Frequency, GHz 4V/μm 2.4V/μm Matching shows weak dependance on DC biasing!!!

26 Tuneable Power Splitters Coplanar Plate (CPS) Parallel Plate

27 Tuneable Matching Networks V1 θ1(v1) Port1 Parallel Plate Port2 Coplanar Plate V2 θ2(v2)

28 Thin film Ba x Sr 1-x TiO 3 (Chalmers) D. Kuylenstierna M. Norling A. Vorobiev A. Deleniv

29 Growth of BST films by laser ablation 0.4 mbar O 2 Laser Rotating Target Ba 0.25 Sr 0.75 TiO x 1 Hz Heater at 650 C PLD System - MC2 Process Lab Chalmers

30 Growth of BST films by rf magnetron sputtering magnet system BSTO 6 target 200W rf Pt/Au/Si substrate Ar ions Ar/O 2 (10/5) 50 mtorr Nordiko 2000 Sputter radiation heater halogen lamps

31 Substrates for ferroelectric microwave Integration devices Issues Crystalline: MgO, LaAlO 3, Al 2 O 3 Polycrystalline: Al 2 O 3 Amorphous: Oxidized Silicon, Fused Silica Metal: Pt, Au, Cu (with diffusion stop buffer)

32 TEM and SEM images of the BSTO films in Thin Film Parallel-Plate Varacotors Top Au/Pt Pt BST BSTO nucleation center Bottom Pt/Au TEM image by Prof. E. Olsson, Chalmers

33 Test Structure Cross Section and Top Electrode Au Au (0.5 μm) -top plate Pt (50 nm) SrTiO 3 (0.56 μm) Pt (200 nm)-bottom plate Au STO or BSTO Top Plate Au/Pt SiO 2 (0.43 μm) Si substrate 0.5 mm Top ground plate, Au/Pt

34 Varactor Performance at 1.0 MHz Capacitance (pf) BST/Pt BST/Pt/Au Q-factor Voltage (V) A. Vorobiev, P. Rundqvist, K. Khamchane, and S. Gevorgian, Appl. Phys. Lett. 83, 3144 (2003)

35 Microwave Performance at V=0 and 20V Capacitance (pf) V 20 V tanδ V 20 V Frequency (GHz) Frequency (GHz) No dispersion in permittivity and tuneability Tuneability > 40 %

36 Technology Comparison. E=0 200 BST/Pt/Au (PLD) GaAs-Schottky Shown are also: Si varactor (Metelics, MSV34,060-C12, 50 MHz, V=-4V) Q-factor BST/Pt (PLD) Si GaAs-HBV 1 10 Frequency (GHz) GaAs HBV (Darmstadt University of Technology, f cut-off =370 GHz) GaAs dual Schottky diode (UMS, DBES105a, f cut-off =2.4 THz)

37 BSTO Potential for Tuneable TFBARs

38 Acoustic Impedances Acoustic impedance Distance from surface Au (63.8) 50 nm Pt (57.6) 300 nm BSTO (42.2) 150 nm Pt (57.6) 0.5 μm Au (63.8) 63.8٠ Si (19.7) 0.45 μm SiO 2

39 Real Part of Impedance (Measured) 0.02 Re(Z)/ V 0 V 20 V Au/Pt/STO/Pt/SiO 2 /Si Frequency, GHz

40 DC Field Dependent Resonance (Measured) V Re{Z}/Im{Z} V Frequency, GHz

41 Device Applications

42 Main Device Fabrication Steps (Prepatterning of bottom electrode) Deposition prepatterning of Pt/Au/Pt (50/500/100nm) bottom electrode Growth of BST film (300nm) by PLD 650 C, 0.4 mbar Top electrode formation by lift-off process

43 Typical Varactor Structures

44 Tuneable Delay Lines Type2

45 Tuneable Delay Line Performance -2.5 S-parameters (0V) E E-11 0V db(s(1,2)) db(s(1,1)) time (s) 7.5E E-11 30V freq, GHz E freq, GHz τ = LC(V ) D. Kuylenstierna et. al, EuMC 2004

46 Lumped Element Tunable Resonators and Filters (a) (b) C S2 /2 C S1 /2 L S2 4L S1 C C L S1 C S2 C C C C C C C S1 L S2 (c) (d)

47 Two-Pole Lumped Element Tunable Filter (simulated) db(s(1,1)) db(s21) freq, GHz freq, GHz D. Kuylenstierna et. al,si RFIC 2006

48 Single Pole Lumped Element Filter (measured) db(s11) db(s21) db(s11) freq, GHz freq, GHz D. Kuylenstierna et. al,si RFIC 2006

49 Tuneable Phase Shifters DC bias 3.6 mm DC bias D. Kuylenstierna et. al, IEEE Micr. Wierless Comp. Letters

50 Tuneable Phase Shifters Mesured S-parameters V 0-5 db(s21) V 0 V db(s11) freq, GHz 15 V Relatively high losses due to steps and surface conductivity of Si D. Kuylenstierna et. al, IEEE Micr. Wierless Comp. Letters

51 Tuneable Phase Shifters Mesured Phase Shift Under 15 V 80 Phase shift [db] Expected phase shift under 25 V: ~90 o freq, GHz D. Kuylenstierna et. al, IEEE Micr. Wierless Comp. Letters

52 Problems and Perspectives

53 Ba x1 Sr 1-x1 TiO 3 Ba x2 Sr 1-x2 TiO 3 Permittivity, ε Paraelectric tanδ Ferroelectric Losses, tanδ Temperature Stabilization (Materials/design based) ε T 2 T 1

54 Temperature Dependence (Materials/Design Based- Measured) Au 2g Au Q Ba 0.75 Sr 0.25 O 3 Ba 0.25 Sr 0.75 O 3 MgO substrate Capacitance, ff Temperature, K C Q-factor

55 Temperature Stabilization (Circuit Topology Based) DC bias network V DC V v L C T V T Varactor C V C

56 Temperature Stabilization (Circuit Topology Based-Summation) E=50 kv/cm Capacitance, pf Not stabilised 0.15 Stabilised Temperature, K

57 Perspective applications : Project HiMission (EUREKA/MEDEA+/VINNOVA ) Phase shifters Tuneable delay Lines Tuneable filters VCO Project Nanostar (FP6, EU) Varactors Tuneable TFBARs VCOs

58 End