2. Evolution of the SAW Transducer for Communication Systems Donald C. Malocha Electrical & Computer Engineering Dept. University of Central Florida Orlando, Fl. 32816-2450 dcm@ece.engr.ucf.edu Special thanks to the UFFC_S and contributing members who initiated, built and maintain the UFFC_S Digital Archive.

3. In recognition of the 50 th Anniversary of the UFFC_S, the presentation will focus on the SAW transducer evolution through the UFFC_S publications. The presentation highlights the development through the “eyes” of the UFFC, not necessarily crediting or citing the first publication, inventor, etc. There is a large body of contributions in other publications, patents, worldwide symposiums, non_English journals, etc., which makes it virtually impossible to site the first disclosure of ideas. Every significant SAW transducer embodiment has eventually graced the pages of UFFC publications. Disclaimer: The material presented does not represent the views of the society fdhfdthftghffdhsdtewratseafowieejfcoiswejvcoiswejefoisiwifvnwomopskefoiwejkfoiwemfoimcwvwejfiowejriofjweoivmoiwejfiwjfiowejifojweiojfg9wer0iwekpvoewpo. Presentation Approach If there are errors or inaccuracies in the presentation, please email me the correct citation(s). Your input is appreciated. dcm@ece.engr.ucf.edu

4. Any sufficiently advance technology is indistinguishable from magic. Arthur C. Clarke

5. SAW Transducer’s Degrees of Freedom Transducer Parameter Degrees of Freedom –Amplitude –Phase –Delay –Frequency Device Infrastructure Degrees of Freedom –Material Choice –Thin Films on the Substrate –Spatial Diversity on the Substrate –Electrical Networks and Interface

6. Introduction _Transduction _Reflection _Re-Generation _Non-Linearity's This presentation addresses the first three properties applicable to SAW transducers

7. Transducer Embodiment Fundamentals –basic bag of tricks Fundamental concepts used in all transducers –Electrodes –Sampling –Apodization

8. Multi- Electrode Transducers “Reflection of a Surface Wave from Three Types of ID Transducer”, A. De Vries, R. Miller and T. Wojcik, 1972 IUS, pp. 353-358 Note: Floating Electrode “Applications of Double Electrodes in SAW Device Design”, T. Bristol, et.al., 1972 IUS, pp. 377-380 Split electrode transducer used to eliminate reflections Minimizes triple transit and self-resonance 3rd Harmonic Operation

9. Transducer Sampling- Harmonics “Surface Acoustic Wave Multielectrode Transducers”, H. Engan, UFFC_T, 1975, pp. 395-401 Note: Floating Electrode

10. First Reference to a Balanced SAW Transducer (Dual Track) “Design of Interdigital Arrays for Acoustic Surface Wave Filters, C. Atzani and L. Masotti, 1972 IUS, pp. 242-252 First introduced with regards to sampling

11. Space Harmonic Control Changing electrode a/p can control harmonics “Space-Harmonic Response of Surface Wave Transducers”, R.D. Weglein and G.R. Nudd, 1972 IUS, pp. 346-352.

12. Interdigitated IDT (IIDT) “SAW Filters Employing Interdigitated Interdigital Transducers, M. Lewis, 1982 IUS, pp.12-17. Interleaved I/O transducers Low loss structure No weighting

13. Low Loss IIDT Antenna Duplexer “Low Loss SAW Filter for Antenna Duplexer”, M. Hikita, T. Tabushi, H. Kojima, A. Nakagoshi and Y. Kinoshita, IUS 1983, pp 77-82. Weighted transducer structure

14. Tap Weighting and Delay Apodization maps ideal tap weights into the spatial profile of the transducer. Idealized attenuated tap weights and electrodes provide delay. “Acoustic Surface Wave Filters”, R. Tancrell, 1969 IUS, pp. 48-64 Uniform spatial profile, variable amplitude Variable spatial profile, uniform amplitude Q: How do we build arbitrary filter responses? A: Use sampling theory and weight the electrodes.

15. FIR Filter to Apodized SAW Transducer Relations between transversal filter, impulse response and SAW transducer. The transducer is a spatial mapping of the time domain response. “Acoustic Surface Wave Filters”, R. Tancrell, 1969 IUS, pp. 48-64.

16. SAW Transducer Sampling “SAW Filter Sampling Technique”, Hunsinger & Kansy, UFFC_T, 1975, pp. 270_273 A SAW transducer can use an arbitrary sampling frequency regardless of center frequency, with a uniform sampling rate, subject to the Nyquist criteria. Not required to use an integer number of electrodes per wavelength to obtain a filter response.

17. Dual Passband Filters “Multipassband Low Loss SAW Filters”, B. Potter & T. Shoquist, 1977 IUS, pp., 736_739.

18. Apodized SAW Filter RF @t=0 Main SAW TTE

19. SAW Apodization Analysis SAW Conductance SAW Apodization Loss Arbitrary SAW Apodization Profile

20. SAW Amplitude Beam Profile as a Function of Frequency - Transfer function assumes a uniform integrating transducer - Conductance vs frequency Amplitude profile vs beam position @ 4 different frequencies

21. Slant Centered Apodized IDT “Low Shape Factor Design Considerations”,P. Meyer, 1975 IUS, pp. 334_335 2 wavelength gaps; in-line; dummy electrodes; split electrode design Slanted transducers SAW transducer schematic; dummy electrodes removed for clarity

22. Acoustic Conductance vs Apodization Technique Each transducer has the exact same impulse response, but the apodization pattern affects the electrical parameters and can be a problem, yielding a poor filter response due to electrical circuit interactions.

23. Example Low Shape Factor Slant-Apodized Transducer Filter

24. Phase Weighting “Phase Weighting for Low Loss Filters”, M. Hikita, Y. Kinoshita, and T. Tabuchi, 1980 IUS, pp. 308-312. Approach a uniform beam profile

25. Distance Weighting “ Acoustic Surface Wave Filters Using New Distance Weighting Technique”, K. Yamanouchi and T. Meguro, IUS 1980, pp. 313-316. Each track is uniform but differing bandwidth/group delay Sum of sampling functions Vary bandwidth by apodization profile Group delay varies with track Structure shown yields linear phase due to symmetry Each track is approximately a rect fcn. Uniform magnitude of beam profile

26. Weighting Techniques Q: How do we weight both transducers to obtain better filter performance? A: Apply tap weighting to the transducer without using apodization Better filter shape factor Smaller device

27. Phase Weighting _ SAW Coded Transducer “Evaluation of Digitally Coded Acoustic Surface Wave Matched Filters”, W. Jones, C.S. Hartmann, and L. Claiborne, UFFC-T, 1971, pp.21-27 Example of matched filter response

28. Block Weighting to a Desired Response “Synthesis of Periodic Unapodized Surface Wave Transducers”, T. Bristol, IUS 1972, pp. 377-380 Phase, block, or a modified withdrawal weighting concept. No apodization but weighted IR. Hamming Function Approximation

29. Withdrawal Weighting “Weighting IDT SAW Transducers by Selective Withdrawal Weighting of Electrodes” C.S. Hartmann, 1973, IUS, pp 423-426 Approximates apodization pattern Works well for small fractional bandwidths Allows weighting of in-line transducers Actually removed electrodes

30. Series Weighted IDT “Series Weighting of SAW Transducers”, H. Engan, 1974 IUS, pp. 422-424 Amplitude Weighted - yields nearly uniform spatial beam profile Uses a voltage divider across the aperture

31. “Combining Series Section Weighting with Withdrawal Weighting in Surface Acoustic Wave Transducers”, F. Sandy, UFFC_T, Vol. 26, No. 4, 1979, pp. 308-312 Combining Series-Withdrawal Weighting

32. Tap Weight Enhancement “Tap Weight Enhancement for Broadband Filters” D.C. Malocha, S. Datta, and B.J. Hunsinger, UFFC-T, 1978, pp. 51-54. Analog tap weight control rather than just unity taps weights

33. Capacitive Tap Weighted Network Uses thin film capacitors fabricated in a multi-level process a) a balance structure b) an unbalanced structure Generates an analog amplitude weighted SAW-uniform spatial beam profile “CTW SAW Transducers”, Malocha & Hunsinger, 1975, IUS, pp. 411-413.

34. Spatial Diversity “Acoustic Radiation Measurements and Calculations for Three Surface Wave Filter Designs”, M. Daniel and J. de Klerk, 1973 IUS, pp.449-455. Apodized, linear dispersive, and slanted transducers. ( Chirp first discussed by R. Tancrell, 1969,1971)

35. Non-Linear Phase Filter Using Dispersive Transducers Single dispersive transducer filter In-line doubly dispersive transducer filter Slanted doubly dispersive filter

36. SAW Slanted Dispersive Transducer “ Surface Acoustic Wave Slanted Correlators for Linear Pulse Compressors”, B. Potter and C.S. Hartmann, IUS 1977, pp. 607-610. Slant provides frequency/spatial diversity and eliminated Fresnel ripple in passband

37. Linear Phase Filter using Dispersive Transducers To 1 st order, flat passband and linear phase.

38. Linear Phase Slanted Transducer “Wide-Band Linear Phase SAW Filter Design Using Slanted Transducer Fingers”, C.K. Campbell, Y. Ye and J. Sferrazza Pappa, UFFC-T, 1982, pp. 224-228. Transition band is determined by impulse response length. Each strip is a relatively narrowband response but the summation is a wideband response. Each strip’s group delay determines whether it is a linear or non-linear phase filter.

39. Slanted Transducer Energy Distribution vs Frequency vs Beam Position Filter response is visualized as the sum of multiple individual narrowband frequency responses which are spatially separated across the transducer aperture. Center of transducer beam Center frequency Mid-band frequency Band-edge frequency Bandwidth is determined by the upper and lower strip band edge frequencies.

40. Example Slanted Transducer Frequency Response

41. Slanted Transducer Weighting Across Passband “Tapered Transducers- Design and Applications”, L. Solie, 1998 IEEE IUS, pp.27-37.

42. Slanted Transducer Weighting Technique “Tapered Transducers- Design and Applications”, L. Solie, 1998 IEEE IUS, pp.27-37. Block weighting is a form of capacitive weighting but allows only discrete amplitude steps. Sidelobes are dependent on weighting of electrodes.

43. Multi-Phase Unidirectional SAW Transducers Q: How do we eliminate bi-directional loss? A: Change 3-port device into 2 port device over bandwidth of interest UDT requires some non-symmetry in transducer/electrical network Theoretically can have 0 dB loss TTE can be zero at center frequency Phasing network determines directivity Matching network determines electrical reflection

44. Three Phase UDT “Wideband Unidirectional Interdigital Surface Wave Transducers”, C.S. Hartmann, W. S. Jones and H. Vollers, UFFC-T, 1972, pp378-381 Requires multi-level crossovers. Requires a 1 or 2 element 60 o degree phase shift network between ports. Requires 1 or 2 element matching network. Unidirectional fractional bandwidth up to approximately 20%.

45. 3 Phase UDT Operation Analyzed as 3 collinear transducers. Unit cell is 1 wavelength; no subharmonics. 1/3 wavelength electrode period; strong 2 nd harmonic

46. 3 Phase UDT – F o Vector Analysis Simulation of forward and reverse responses

47. Quadrature 3-Phase “Quadrature 3 Phase Unidirectional Transducer”, D.C. Malocha, UFFC-T, Vol.26, no. 4, 1979, pp. Forward response Reverse response

48. Apodized 3Phase UDT

49. Three Phase UDT Low Loss Filter Results Wide Band Filter Response Narrowband Filter Response

50. Group-Type UDT (GUDT) “Low Insertion Loss Acoustic Surface Wave Filter Using Group-Type Unidirectional Interdigital Filter Transducer”, IUS, 1975, K. Yamanouchi, F. Nyffeler and K. Shibayama, pp. 317- 321 Single level fabrication Electrical phase shift network of 45 o (1 or 2 elements) and matching network (often 1 element) is used with the spatial offset such that a SAW is launched in one direction over a determined bandwidth. Phasing always yields real input impedance; proper beam width choice eliminates separate matching network.

51. Group-Type UDT ++ ++ ++ ++ I-Inphase Q- Quadrature I-Inphase Joining of transducers eliminates a wavelength within each unit cell composed of an I and Q port. GUDT uses interleaved transducers which are spatially offset from synchronism by an integer number plus one quarter wavelength. Single level metallization – no crossovers.

52. GUDT Simulated F/R Responses The number of electrodes in the transducer sub-units is determined from design criteria. Sub-harmonics are generated from I-Q spacing. Typical fractional bandwidth <15%.

53. Single Phase UDT (SPUDT) Q: How can TTE be reduced w/o multi-phase UDT? A: Use internal transducer mechanical reflections to cancel regeneration Nearly eliminates TTE Requires 1 (or 2 matching) elements Works like a UDT-lowers insertion loss; theoretically as low as 0dB

54. Original Single Phase UDT (SPUDT) “A Triple Transit Suppression Technique”, K. Hanma and B.J Hunsinger, 1976, IUS, pp. 328-331 By matching the magnitudes and opposing phases of the acousto-mechanical reflection and the reflected acousto- electric wave the net reflected wave from an acoustic port can be minimized.

55. The transducer is composed of a transduction and reflection structure. The reflecting structure may be incorporated into the transducer structure or can be superimposed onto the transduction structure. The reflector can be made by mass loading of metal, grooves, or dielectric material. SPUDT Schematic Concept

56. SPUDT Macroscopic Reflection The figure above illustrates schematically how a SPUDT operates. The mechanical wave is equal in amplitude but 180 o out of phase with the regenerated wave. First order analysis w/o cross coupling and first order reflection. Figure: Abbott PhD Thesis1989

57. Single Phase UDT - Evolution “An Analysis of SAW Interdigital Transducers With Internal Reflections and the Application to the Design of Single-Phase Unidirectional Transducers”, C.S. Hartmann, P.V. Wright, R.J. Kansy and E.M. Garber, IUS, 1982, pp. 40-45. Multi-level transducer with a reflective grating

58. EWC -SPUDT Basic Unit Cells A)Transduction and reflector B)Transduction and no reflector C)Reflector without transduction D)No transduction and no reflector. “Overview of Design Challenges for Single Phase Unidirectional SAW Filters”, C.S. Hartmann and B.P. Abbott, IUS 1989, pp. 79-89. Schematic example of Electrode Width Controlled SPUDT

59. Distributed Acoustic Reflecting Transducer (DART) “Design of Low Loss SAW Filters Employing Distributed Acoustic Reflection Transducers”, T. Kodama, H. Kawabata, Y. Yasuhara and H. Sato, 1986 IUS, pp. 59-64.

60. Floating Electrode UDT (FEUDT) “ Low –Loss SAW Filter Using Internal Reflection Type of New Single Phase Unidirectional Transducer, K. Yamanouchi and H. Furuyashiki, IUS 1984, pp. 68-71. Shorted or open electrode configuration changes the transduction/reflector interaction and “selects” forward/reverse directivity.

61. Example of SPUDT Time/Frequency TTE Main SAW Insertion loss ~ 5 dB

62. Early Single Level SPUDT “Low Loss SAW Devices Employing Single Stage Fabrication”, M. Lewis, IUS 1983, pp.104-108, Transducer is comb structure with internal series of reflectors Comb produces sub-harmonics Single level fabrication

63. Slanted SPUDT “Improved Design of Single-Phase UDT for Low Loss SAW Filters, C.B. Saw and C.K. Campbell, IUS 1987,pp. 169-172 Combining the SPUDT concept to slanted transducers provided both a wideband transduction and reflection mechanism. Represents a single track of a Slanted SPUDT

64. SPUDT Slanted Transducer Configuration Each strip’s reflectors have a narrowband response around the strip’s center frequency The electrical transduction and mechanical reflections are narrowband is each strip The overall filter response is the sum of narrowband responses, which is wideband. Conventional SPUDT: Mechanical reflectors have only a narrowband response around the filter center frequency, SPUDT net effect is narrowband “Tapered Transducers- Design and Applications”, L. Solie, 1998 IEEE IUS, pp.27-37.

65. SPUDT Slanted Transducer Filter “Tapered Transducers- Design and Applications”, L. Solie, 1998 IEEE IUS, pp.27-37.

66. “The Natural Single-Phase Unidirectional Transducer: A New Low-Loss SAW Transducer”, P.V. Wright, IUS 1985, pp. 58-63. Natural Single Phase Unidirectional Transducer (NSPUDT) For some cuts of material, the transducer/crystal cut combination is “naturally unidirectional”. The effective center of transduction can be within/near the electrode region- this makes a spatial asymmetry in the transducer with respect to the transduction/reflection centers. Quarter-wavelength electrodes are used for the mechanical reflection. Problem: transducer only “looks” in one direction.

67. Resonant SPUDT (RSPUDT) “ A New Concept in SPUDT Design: the RSPUDT (Resonant SPUDT)”, P. Ventura, M. Solal, P. Dufilie, J.M. Hode, and F., Roux. IUS 1994, pp. 1-6.

68. Waveguide SPUDT “New SPUDT Cell Structure”, G. Martin, H. Schmidt, and B. Wall, 2002 IUS, pp. 39-42.

69. Harmonic SPUDT (HSPUDT) “A New Type SPUDT for use in High Frequency around 2 GHz”, C_Y. Jian and S. Beaudin, 2002 IUS, pp. 279-282. Slanted HSPUDT

70. SAW Propagation Simulation Don’t Panic!!! Diffraction – the Designer’s “Alibi” What do you do when your filter doesn’t meet specs?!

71. Some Concluding Remarks SAW devices have a limited future in filtering – CCDs will take over signal processing applications (circa 1979) SAW RF filters with low insertion loss are merely laboratory curiosities. SAW devices will have an estimated world wide market of about $250,000 (circa 1985). SAW RF filters should be reduced in cost from $2.00 to less than $.50 within 5 years. (circa 1994) SAW IF filters will be eliminated in all cellular radios by zero- IF by 2002. LGX is the material of the future, and always will be!! By the way, what is an effervescent wave ?? We came, we SAW, we conquered ! My crystal ball is fuzzy, so I’ll refer to some unidentified quotes of my predecessors: SAW technology is mature but still evolving. To our colleagues who developed the past SAW technology, we salute you !!! You now have seen some of the tricks of the trade !