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MEMS Two-Phase Vapor Escape Heat Exchanger

MEMS Two-Phase Vapor Escape Heat Exchanger. Milnes David Tarun Khurana Christopher Anderson. Process Flow. Diffusion Clean Oxide Growth Al. Sputter Backside Pattern (heaters & sensors) Al Etch Ashing PRX 1000 Clean Backside LTO deposition Backside protect Front-side Oxide Etch (HF)

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MEMS Two-Phase Vapor Escape Heat Exchanger

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  1. MEMS Two-Phase Vapor Escape Heat Exchanger Milnes David Tarun Khurana Christopher Anderson

  2. Process Flow • Diffusion Clean • Oxide Growth • Al. Sputter • Backside Pattern (heaters & sensors) • Al Etch • Ashing • PRX 1000 Clean • Backside LTO deposition • Backside protect • Front-side Oxide Etch (HF) • Front-side pattern (channels) • Front-side channel etch (STSDRIE) • Backside pattern (bond pads) • Pad etch

  3. Process Layout • Backside pattern (through etch) • Through etch (STS DRIE) • Final released device • Adhesive coat on transfer substrate • Contact printing of adhesive • Membrane attachment via UV curing • Attachment of patterned double sticky tape (vapor channel) • Top cover integration

  4. Images of the Heaters and Sensor open bond pads

  5. Typical Defects • Shorts (bridging) • Voids • Scratches – due to handling errors, motivates thicker LTO deposition (5000 A)

  6. Resistance Measurements 4.4 250 ? 150 401 385 506 400 43 389 44 ? 42 383 43 381 410 393 397 380 423 367 5.0 Ground lines = 4.7 ± 0.4  Sensors = 392 ± 15  Heaters = 43 ± 0.8  In all cases resistance is almost twice as high as predicted.

  7. LTO300 Deposition Average dep rate: alternate arrangement = 58 A/min Consecutive arrangement = 40 A/min Average etch rate pad-etch rate: LTO oxide = 3540 A/min Thermal oxide = 400-600 A/min

  8. STS issues • STS down for a month, expected to be up by 1st week of Aug. • Alternatives Pursued: • Getting trained on STS2 (through-etch still not possible) • Outside DRIE and machining service vendors • American precision dicing (can do through etch features) • Laserod laser machining (~ $200 per wafer) • ISSYS • Honeywell MEMS foundry • IMT • Investigated UC-Berkeley and UCSB fab • Training and qualification time is an issue (about a week in each case) • Investigating wet etch options (KOH or TMAH) • Requires oxide or nitride as mask • Significant undercutting can result in much larger features • Changing process flow to perform pad etch first to save time. • Created back-up device in Copper.

  9. Design of Copper Device

  10. Thanks! Questions?

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