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Micromachined Antennas for Integration with Silicon Based Active Devices

Micromachined Antennas for Integration with Silicon Based Active Devices. Erik Öjefors Signals and Systems, Dep.of Engineering Sciences Uppsala University, Sweden. Outline of talk. Introduction, applications Challenges of on-chip antenna integration Design of 24 GHz on-chip antennas

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Micromachined Antennas for Integration with Silicon Based Active Devices

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  1. Micromachined Antennas for Integration with Silicon Based Active Devices Erik Öjefors Signals and Systems, Dep.of Engineering Sciences Uppsala University, Sweden Micromachined Antennas for Integration with Silicon Based Active Devices

  2. Outline of talk • Introduction, applications • Challenges of on-chip antenna integration • Design of 24 GHz on-chip antennas • Crosstalk with on-chip circuits • Micromachined antenna packaging • Conclusions and future work Micromachined Antennas for Integration with Silicon Based Active Devices

  3. RFIC LNA RF IF PA LO RF Crystal VCO Oscillator 12 GHz 20 MHz PLL DC SHM acting as a frequency doubler 1/8 Introduction Objective On-chip antenna integrated with a 24 GHz ISM band transceiver in SiGe HBT technology for short range RADAR and communication devices Integration Antenna Self-contained SiGe front-end 3x3 mm large chip Micromachined Antennas for Integration with Silicon Based Active Devices

  4. Introduction One application RADAR for traffic surveillance and anti-collision warning systems Micromachined Antennas for Integration with Silicon Based Active Devices

  5. Introduction • Advantages of integrated antenna: • Simplified packaging (no high frequency interconnects) • Lowered cost due to reduced number of components • Omnidirectional radiation pattern often needed, • low gain on-chip antenna feasible Micromachined Antennas for Integration with Silicon Based Active Devices

  6. 2a Challenges of on-chip antenna integration Antenna size can NOT be reduced without consequences! Minimum Q (quality factor) of small antennas “a” is the radius of a sphere enclosing the antenna. “k” = 2p/l. High Q leads to small bandwidth and can reduce the efficiency McClean, " A Re-examination of the Fundamental Limits on the Radiation Q of Electrically Small Antennas," IEEE Trans AP, May 1996. Micromachined Antennas for Integration with Silicon Based Active Devices

  7. Challenges of on-chip antenna integration Problem: Size of antenna is an important parameter due to the high cost of the processed SiGe wafer Solution: Chose antenna types which offer compact integration with the active circuits Micromachined Antennas for Integration with Silicon Based Active Devices

  8. Proposed integration with active devices Slot antenna Active devices Active elements integrated within slot loop 3 mm Top metallization 3 mm Active devices Si p+ channel stopper Micromachined Antennas for Integration with Silicon Based Active Devices

  9. Challenges of on-chip antenna integration Problem: Commercial silicon-germanium (SiGe) semiconductor use low resisistivity (< 20 Wcm) substrates Solution: Use of a low loss interface material such as BCB polymer or micromachining to reduce coupling between antenna and lossy silicon substrate Micromachined Antennas for Integration with Silicon Based Active Devices

  10. Micromachining Micromachining– mechanical shaping of silicon wafers by semi-conductor processing techniques Micromachined Antennas for Integration with Silicon Based Active Devices

  11. Micromachining – BCB process flow Post processing technique compatible with pre-processed SiGe wafers from commercial semiconductor foundaries Active circuit Pre-processed wafer from foundary Si BCB 10-20 um BCB layer applied and cured Si Gold Top metallization evaporated and defined using standard photolitho- graphic techniques Si Micromachined Antennas for Integration with Silicon Based Active Devices

  12. Micromachining Surface micromachining of silicon Top metali zation Slot Optional micro - BCB, machining 20 um 10 um W Si 11 - 15 cm Surface micromachining applied to the substrate before BCB-spin-on Micromachined Antennas for Integration with Silicon Based Active Devices

  13. Bulk micromachining of silicon Micromachining Top metali zation Slot 10-20 um BCB membrane, Backside etching Si Back side of silicon substrate etched as last step in processing Micromachined Antennas for Integration with Silicon Based Active Devices

  14. Outline of talk • Introduction, applications • Challenges of on-chip antenna integration • Design of 24 GHz on-chip antennas • Crosstalk with on-chip circuits • Micromachined antenna packaging • Conclusions and future work Micromachined Antennas for Integration with Silicon Based Active Devices

  15. Micromachined 24 GHz antennas • Surface micromachined slot loop antenna • Bulk micromachined slot loop antenna • Inverted F antenna • Wire loop antenna • Meander dipole • Differential patch antenna • Comparison of designed antennas Micromachined Antennas for Integration with Silicon Based Active Devices

  16. Surfaced micromachined slot loop antenna Micromachined 24 GHz antennas BCB, Si 10, 20 um slot width 3000 um CPW probe pad BCB 10-20 um Si 11-15 Wcm 2000 um 3000 um Slot loop length corresponds to one guided wavelength at 22 GHz Micromachined Antennas for Integration with Silicon Based Active Devices

  17. Micromachined 24 GHz antennas Surfaced micromachined slot loop antenna Small return loss outside the the operating frequency indicates that losses are present Micromachined Antennas for Integration with Silicon Based Active Devices

  18. Results – Radiation Pattern Antenna on 20 um thick BCB interface layer on low resistivity Si H-plane E-plane Reasonably good agreement between simulated and measured radiation pattern, (some shadowing in E-plane caused by measurement setup) Micromachined Antennas for Integration with Silicon Based Active Devices

  19. AUT Micromachined 24 GHz antennas Results – Gain and efficiency Reference horn antenna • Measured gain: -3.4 dBi • Directivity (simulated): 3.2 dBi • Calculated efficiency: 20 % Wafer probe station 80 cm Foam material (low dielectric constant) Micromachined Antennas for Integration with Silicon Based Active Devices

  20. Micromachined 24 GHz antennas Bulk micromachining – improving efficiency Slot supported by BCB membrane Si 200 m No trenches Trenches can be formed from the back side of the wafer by chemical wet etching (KOH) or dry etching (DRIE) methods Micromachined Antennas for Integration with Silicon Based Active Devices

  21. Micromachined 24 GHz antennas Bulk micromachining – improving efficiency Radiating slots • DRIE • >100 um trench width can be etched Radiating slots Anisotropic etching (KOH, TMAH) Needs wafer thinning (300 um) Micromachined Antennas for Integration with Silicon Based Active Devices

  22. Micromachined 24 GHz antennas • Bulk micromachining 3D-FEM simulations (HFSS) By etching 200 um wide trenches in the silicon wafer the simulated input impedance is increased from 60 W to 210 W at the second resonance, simulated efficiency increased from 20% to >50% Micromachined Antennas for Integration with Silicon Based Active Devices

  23. Bulk Micromachining – Slot Loop Antenna Micromachined slot loop antenna sa Si wt Trench (membrane) Slot • Designed antenna • Trench width wt = 100 um • Results • Measured gain 0-1 dBi • Single ended feed (CPW) • Impedance 100 Ohm Silicon space for active devices wb lg wt Slot Top metallization (groundplane) lg Micromachined Antennas for Integration with Silicon Based Active Devices

  24. Micromachined 24 GHz antennas Inverted F Antenna Micromachined Antennas for Integration with Silicon Based Active Devices

  25. Micromachined 24 GHz antennas Si Wtr Inverted F antenna on membrane Ltr LF Ltr Wtr • Bent quarterwave radiator formed by offset fed inverted F • Inverted F radiator placed on 2.6 x 0.9 mm BCB membrane • Single ended feed HF Membrane CPW feed Space for circuits LGP WGP Micromachined Antennas for Integration with Silicon Based Active Devices

  26. Micromachined 24 GHz antennas Inverted F antenna on membrane • Measured input impedance • 50 W at 24 GHz • Measured gain 0 dBi • Antenna tuning sensitive to ground plane size Micromachined Antennas for Integration with Silicon Based Active Devices

  27. Micromachined 24 GHz antennas Wire loop antennas Micromachined Antennas for Integration with Silicon Based Active Devices

  28. Micromachined 24 GHz antennas Wire loop antenna on micromachined silicon Micromachined Antennas for Integration with Silicon Based Active Devices

  29. Trench Slot Si space for active devices Wbr Wtr LL Top metallization (ground-plane) Wc Micromachined 24 GHz antennas 24 GHz wire loop antenna on micromachined silicon • 3 x 3 mm wire loop • 360 um wide BCB trenches • covered with BCB membranes • Chip size 3.6 x 3.6 mm • Differential feed • Measured input impedance • 75 W at 24 GHz • Measured gain 1-2 dBi Lc Si Wtr Micromachined Antennas for Integration with Silicon Based Active Devices

  30. Micromachined 24 GHz antennas Meander dipole antenna Micromachined Antennas for Integration with Silicon Based Active Devices

  31. Micromachined 24 GHz antennas Meander Dipole on BCB membrane 3.3 mm 0.9 mm Membrane Silicon • Membrane size 3.3 x 0.9 mm • Differential feed • Input impedance at 24 GHz 20W • Measured antenna gain 0 dBi Antenna BCB Silicon Wtr Micromachined Antennas for Integration with Silicon Based Active Devices

  32. Micromachined 24 GHz antennas Patch antennas Micromachined Antennas for Integration with Silicon Based Active Devices

  33. Micromachined 24 GHz antennas Differentially fed patch antenna by University of Ulm Patch 3800 um BCB 30 um Polarization Si Ground-plane SiGe • Differential feed – no ground connection • Suitable for wafer scale packaging • Disadvantages – small bandwidth Feed point 2000 um Micromachined Antennas for Integration with Silicon Based Active Devices

  34. Micromachined 24 GHz antennas Differentially fed patch antenna transmission line model Modelled return loss Micromachined Antennas for Integration with Silicon Based Active Devices

  35. Comparison of 24 GHz Antennas Micromachined Antennas for Integration with Silicon Based Active Devices

  36. Outline • Introduction, applications • Challenges of on-chip antenna integration • Design and results for implemented antennas • Crosstalk with on-chip circuits • Micromachined antenna packaging • Conclusions and future work Micromachined Antennas for Integration with Silicon Based Active Devices

  37. Crosstalk with active circuits Slot mode E - field Parallel - plate BCB mode p+ layer, active device area W Si 11 - 15 cm Parallel plate modes can be excited between the antenna groundplane and conductive active device area Micromachined Antennas for Integration with Silicon Based Active Devices

  38. Crosstalk with active circuits BCB substrate Slot mode E - field contact BCB p+ layer, active W Si 11 - 15 cm circuit ground Parallel plate modes short circuited by BCB via to substrate, crosstalk improvement of 30 dB possible in some cases Micromachined Antennas for Integration with Silicon Based Active Devices

  39. Outline of talk • Introduction, applications • Challenges of on-chip antenna integration • Design and results for implemented antennas • Crosstalk with on-chip circuits • Micromachined antenna packaging • Conclusions and future work Micromachined Antennas for Integration with Silicon Based Active Devices

  40. Glob top Si Active devices LTCC carrier Packaging of Micromachined Antennas • LTCC (Low Termperature Co-fired Ceramic) used as a carrier for • flip-chip or wire-bonded device • Glob-top encapsulation obviates the need for a packaging lid Micromachined Antennas for Integration with Silicon Based Active Devices

  41. Glob-top Type Loss tangent Dielectric constant Amicon S 7503 Silicone 0.0005 / 1 kHz 3.1 Semicosil 900LT Silicone 0.005 / 50 Hz 3.0 Lord CircuitSaf TM ME-455 Epoxy cavity fill 0.006 / 1 MHz 3.37 Lord CircuitSaf TM ME-430 Epoxy glob top 0.006 / 1 MHz 3.7 Namics XV6841-0209 Side fill 0.008 / 1 MHz 3.5 Packaging of Micromachined Antennas Micromachined Antennas for Integration with Silicon Based Active Devices

  42. Packaging - Evaluated Glob-tops Micromachined Antennas for Integration with Silicon Based Active Devices

  43. Packaging – glob top characterization Measured resonator insertion loss – single tape (100 um dielectric) Micromachined Antennas for Integration with Silicon Based Active Devices

  44. Glob-top Single layer fr [GHz] Double layer fr [GHz] Single layer Q0 Double layer Q0 No glob-top / Air 24.67 24.85 95 75 Amicon S 7503 23.14 23.44 75 50 Semicosil 900LT 23.41 23.98 67 65 Lord CircuitSaf ME-455 22.84 23.26 95 72 Lord CircuitSaf ME-430 22.66 22.87 95 67 Namics XV6841-0209 22.78 22.96 87 71 Packaging – glob top characterization Micromachined Antennas for Integration with Silicon Based Active Devices

  45. Packaging - Summary • A low cost packaging method for 24 GHz MMIC’s is • proposed • Ferro A6-S ceramic LTCC evaluated at 24 GHz • Glob-top, cavity fill and side fill polymers characterized - • epoxy based materials better than silicone ones Micromachined Antennas for Integration with Silicon Based Active Devices

  46. Packaging – future and ongoing work • Membrane / glob-top compatibility • Preliminary results promising – no membrane breakage for > 10 mm2 membranes covered with BCB glob tops • Glob-top covered antennas – electrical performance • Glop-top covered loop and dipole antennas mounted on standard FR4 printed circuit boards – characterization pending Micromachined Antennas for Integration with Silicon Based Active Devices

  47. Outline • Introduction, applications • Challenges of on-chip antenna integration • Design and results for implemented antennas • Crosstalk with on-chip circuits • Micromachined antenna packaging • Conclusions and future work Micromachined Antennas for Integration with Silicon Based Active Devices

  48. Conclusions • Integration of an on-chip antenna with a 24 GHz • circuits in SiGe technology has been proposed • 24 GHz on-chip antennas, suitable for integration, • have been manufactured and evaluated • Micromachining of the silicon substrate yields antennas • with reasonable efficiency • Simple glob-top packaging for micromachined • antennas has been evaluated Micromachined Antennas for Integration with Silicon Based Active Devices

  49. Future and ongoing work • Characterization and modeling of the manufactured • antennas • Improve antenna measurement techniques • Integrate the antenna with SiGe receiver/transmitter • Demonstrate packaging of micromachined antennas • Integrate opto-electronic devices with antennas Micromachined Antennas for Integration with Silicon Based Active Devices

  50. Future and ongoing work Ring slot antenna integrated with 24 GHz receiver* being manufactured Micromachined trenches to be inserted in silicon Slot in metal 3 3 mm Receiver Substrate contacts Transistor test structures *Receiver is designed by University of Ulm 3 mm Micromachined Antennas for Integration with Silicon Based Active Devices

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