Aug 2004 Micromachined Antennas for Integration with Silicon Based Active Devices Erik Öjefors Signals and Systems, Dep.of Engineering Sciences Uppsala University, Sweden

Aug 2004 Micromachined Antennas for Integration with Silicon Based Active Devices 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 Outline of talk

Aug 2004 Micromachined Antennas for Integration with Silicon Based Active Devices Introduction Objective On-chip antenna integrated with a 24 GHz ISM band transceiver in SiGe HBT technology for short range RADAR and communication devices PLL 1/8 VCO 12 GHz Crystal Oscillator 20 MHz DC IF LO RF SHM acting as a frequency doubler PA LNA RFIC Antenna Self-contained SiGe front-end Integration 3x3 mm large chip

Aug 2004 Micromachined Antennas for Integration with Silicon Based Active Devices Introduction One application RADAR for traffic surveillance and anti-collision warning systems

Aug 2004 Micromachined Antennas for Integration with Silicon Based Active Devices 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

Aug 2004 Micromachined Antennas for Integration with Silicon Based Active Devices Challenges of on-chip antenna integration Minimum Q (quality factor) of small antennas “a” is the radius of a sphere enclosing the antenna. “k” = 2  /  High Q leads to small bandwidth and can reduce the efficiency 2a McClean, " A Re-examination of the Fundamental Limits on the Radiation Q of Electrically Small Antennas," IEEE Trans AP, May Antenna size can NOT be reduced without consequences!

Aug 2004 Micromachined Antennas for Integration with Silicon Based Active Devices 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

Aug 2004 Micromachined Antennas for Integration with Silicon Based Active Devices Proposed integration with active devices Si Active devices Slot antenna Active devices Top metallization 3 mm Active elements integrated within slot loop 3 mm p+ channel stopper

Aug 2004 Micromachined Antennas for Integration with Silicon Based Active Devices Challenges of on-chip antenna integration Problem: Commercial silicon-germanium (SiGe) semiconductor use low resisistivity (< 20  cm) substrates Solution: Use of a low loss interface material such as BCB polymer or micromachining to reduce coupling between antenna and lossy silicon substrate

Aug 2004 Micromachined Antennas for Integration with Silicon Based Active Devices Micromachining – mechanical shaping of silicon wafers by semi- conductor processing techniques Micromachining

Aug 2004 Micromachined Antennas for Integration with Silicon Based Active Devices Post processing technique compatible with pre-processed SiGe wafers from commercial semiconductor foundaries Si Active circuit Si BCB Gold Pre-processed wafer from foundary um BCB layer applied and cured Top metallization evaporated and defined using standard photolitho- graphic techniques Micromachining – BCB process flow

Aug 2004 Micromachined Antennas for Integration with Silicon Based Active Devices Surface micromachining of silicon BCB, 20 um 10 um Si  cm Slot Optional micro- machining Top metalization Surface micromachining applied to the substrate before BCB-spin-on Micromachining

Aug 2004 Micromachined Antennas for Integration with Silicon Based Active Devices Bulk micromachining of silicon BCB membrane, um Slot Backside etching Top metalization Back side of silicon substrate etched as last step in processing Micromachining Si

Aug 2004 Micromachined Antennas for Integration with Silicon Based Active Devices 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

Aug 2004 Micromachined Antennas for Integration with Silicon Based Active Devices 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

Aug 2004 Micromachined Antennas for Integration with Silicon Based Active Devices Surfaced micromachined slot loop antenna CPW probe pad Slot loop length corresponds to one guided wavelength at 22 GHz 2000 um 3000 um Si  cm BCB um 10, 20 um slot width BCB, Si Micromachined 24 GHz antennas

Aug 2004 Micromachined Antennas for Integration with Silicon Based Active Devices Small return loss outside the the operating frequency indicates that losses are present Surfaced micromachined slot loop antenna Micromachined 24 GHz antennas

Aug 2004 Micromachined Antennas for Integration with Silicon Based Active Devices Results – Radiation Pattern Antenna on 20 um thick BCB interface layer on low resistivity Si E-plane H-plane Reasonably good agreement between simulated and measured radiation pattern, (some shadowing in E-plane caused by measurement setup)

Aug 2004 Micromachined Antennas for Integration with Silicon Based Active Devices Measured gain: -3.4 dBi Directivity (simulated): 3.2 dBi Calculated efficiency: 20 % 80 cm Reference horn antenna Foam material (low dielectric constant) AUT Wafer probe station Results – Gain and efficiency Micromachined 24 GHz antennas

Aug 2004 Micromachined Antennas for Integration with Silicon Based Active Devices 200  m Si Slot supported by BCB membrane Trenches can be formed from the back side of the wafer by chemical wet etching (KOH) or dry etching (DRIE) methods No trenches Micromachined 24 GHz antennas Bulk micromachining – improving efficiency

Aug 2004 Micromachined Antennas for Integration with Silicon Based Active Devices Bulk micromachining – improving efficiency Anisotropic etching (KOH, TMAH ) Needs wafer thinning (300 um) DRIE >100 um trench width can be etched Radiating slots Micromachined 24 GHz antennas

Aug 2004 Micromachined Antennas for Integration with Silicon Based Active Devices Bulk micromachining 3D-FEM simulations (HFSS) By etching 200 um wide trenches in the silicon wafer the simulated input impedance is increased from 60  to 210  at the second resonance, simulated efficiency increased from 20% to >50% Micromachined 24 GHz antennas

Aug 2004 Micromachined Antennas for Integration with Silicon Based Active Devices Bulk Micromachining – Slot Loop Antenna Designed antenna Trench width wt = 100 um Results Measured gain 0-1 dBi Single ended feed (CPW) Impedance 100 Ohm Slot Top metallization (groundplane) Slot wb lg Si wt sa Trench (membrane) wt Micromachined slot loop antenna Silicon space for active devices

Aug 2004 Micromachined Antennas for Integration with Silicon Based Active Devices Micromachined 24 GHz antennas Inverted F Antenna

Aug 2004 Micromachined Antennas for Integration with Silicon Based Active Devices Si W tr LFLF W GP L tr W tr HFHF L GP L tr CPW feed Membrane Space for circuits Inverted F antenna on membrane 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 Micromachined 24 GHz antennas

Aug 2004 Micromachined Antennas for Integration with Silicon Based Active Devices Micromachined 24 GHz antennas Inverted F antenna on membrane Measured input impedance 50  at 24 GHz Measured gain 0 dBi Antenna tuning sensitive to ground plane size

Aug 2004 Micromachined Antennas for Integration with Silicon Based Active Devices Micromachined 24 GHz antennas Wire loop antennas

Aug 2004 Micromachined Antennas for Integration with Silicon Based Active Devices Micromachined 24 GHz antennas Wire loop antenna on micromachined silicon

Aug 2004 Micromachined Antennas for Integration with Silicon Based Active Devices 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  at 24 GHz Measured gain 1-2 dBi Lc Slot Top metallization (ground-plane) Trench W br W tr Wc L Si space for active devices Si W tr

Aug 2004 Micromachined Antennas for Integration with Silicon Based Active Devices Micromachined 24 GHz antennas Meander dipole antenna

Aug 2004 Micromachined Antennas for Integration with Silicon Based Active Devices Micromachined 24 GHz antennas W tr Antenna BCB Silicon Membrane 3.3 mm 0.9 mm Membrane size 3.3 x 0.9 mm Differential feed Input impedance at 24 GHz 20  Measured antenna gain 0 dBi Meander Dipole on BCB membrane

Aug 2004 Micromachined Antennas for Integration with Silicon Based Active Devices Patch antennas Micromachined 24 GHz antennas

Aug 2004 Micromachined Antennas for Integration with Silicon Based Active Devices Differentially fed patch antenna by University of Ulm Differential feed – no ground connection Suitable for wafer scale packaging Disadvantages – small bandwidth Si Feed point BCB Patch Ground-plane 30 um 3800 um 2000 um Micromachined 24 GHz antennas Polarization SiGe

Aug 2004 Micromachined Antennas for Integration with Silicon Based Active Devices Micromachined 24 GHz antennas Modelled return loss Differentially fed patch antenna transmission line model

Aug 2004 Micromachined Antennas for Integration with Silicon Based Active Devices Comparison of 24 GHz Antennas Slot loop antenna Wire loop antenna Meander dipole Inverted F antenna Patch antenna Size at 24 GHz Trenches, die size 3.3 x 3.3 mm Trenches, die size 3.6 x 3.6 mm Membrane size 3.3 x 0.76 mm Membrane size 2.6 x 0.9 mm Thick BCB area of 3.8 x 1.9 mm Feed type and impe- dance Single ended  Differential  Differential  Single ended 50  Differential typically 50  Gain0-1 dBi1-2 dBi0 dBi < 7 dBi RemarkCircuits within antenna footprint Sensitive to size of on- chip ground Wafer level integration

Aug 2004 Micromachined Antennas for Integration with Silicon Based Active Devices 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 Outline

Aug 2004 Micromachined Antennas for Integration with Silicon Based Active Devices Crosstalk with active circuits BCB Si  cm Slot mode E-field Parallel-plate mode p+ layer, active device area Parallel plate modes can be excited between the antenna groundplane and conductive active device area

Aug 2004 Micromachined Antennas for Integration with Silicon Based Active Devices Crosstalk with active circuits Slot mode E-field BCB Si  cm BCB substrate contact p+ layer, active circuit ground Parallel plate modes short circuited by BCB via to substrate, crosstalk improvement of 30 dB possible in some cases

Aug 2004 Micromachined Antennas for Integration with Silicon Based Active Devices 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

Aug 2004 Micromachined Antennas for Integration with Silicon Based Active Devices Si Glob top Active devices LTCC carrier 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 Packaging of Micromachined Antennas

Aug 2004 Micromachined Antennas for Integration with Silicon Based Active Devices Packaging of Micromachined Antennas Glob-topTypeLoss tangent Dielectric constant Amicon S 7503Silicone / 1 kHz 3.1 Semicosil 900LTSilicone0.005 / 50 Hz 3.0 Lord CircuitSaf TM ME-455 Epoxy cavity fill / 1 MHz 3.37 Lord CircuitSaf TM ME-430 Epoxy glob top / 1 MHz 3.7 Namics XV Side fill0.008 / 1 MHz 3.5

Aug 2004 Micromachined Antennas for Integration with Silicon Based Active Devices Packaging - Evaluated Glob-tops

Aug 2004 Micromachined Antennas for Integration with Silicon Based Active Devices Packaging – glob top characterization Measured resonator insertion loss – single tape (100 um dielectric)

Aug 2004 Micromachined Antennas for Integration with Silicon Based Active Devices Packaging – glob top characterization Glob-topSingle layer f r [GHz] Double layer f r [GHz] Single layer Q 0 Double layer Q 0 No glob-top / Air Amicon S Semicosil 900LT Lord CircuitSaf ME Lord CircuitSaf ME Namics XV

Aug 2004 Micromachined Antennas for Integration with Silicon Based Active Devices 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

Aug 2004 Micromachined Antennas for Integration with Silicon Based Active Devices Packaging – future and ongoing work Membrane / glob-top compatibility Preliminary results promising – no membrane breakage for > 10 mm 2 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

Aug 2004 Micromachined Antennas for Integration with Silicon Based Active Devices 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 Outline

Aug 2004 Micromachined Antennas for Integration with Silicon Based Active Devices 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

Aug 2004 Micromachined Antennas for Integration with Silicon Based Active Devices 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

Aug 2004 Micromachined Antennas for Integration with Silicon Based Active Devices Ring slot antenna integrated with 24 GHz receiver* being manufactured 3 mm Receiver Transistor test structures Slot in metal 3 Micromachined trenches to be inserted in silicon Substrate contacts *Receiver is designed by University of Ulm Future and ongoing work

Aug 2004 Micromachined Antennas for Integration with Silicon Based Active Devices Acknowledgements The entire ARTEMIS consortium: Staff at University of Ulm, CNRS/LAAS Toulouse, Atmel GmbH, Sensys Traffic, VTT Electronics Klas Hjort and Mikael Lindeberg at Ångström Laboratory This work was financially supported by the European Commision through the IST-program