Ultra Low- Power Sensors for Con2nuous Current Monitoring. Christopher Sherman, Prof Paul Wright, Prof Dick White 9/17/2013

Transcription

1 Ultra Low- Power Sensors for Con2nuous Current Monitoring Christopher Sherman, Prof Paul Wright, Prof Dick White 9/17/2013

2 Intro and Mo2va2on Smart grid needs smart sensors Goal is small, inexpensive, low power, wireless sensing 9/19/13 2

3 Current Sensor Design Space Sensor Size Small Large Rogowski coil Clamp- on meter Kill- a- WaO Commercial 3- phase meter Our Sensor Hall Sensor AMR Sensor Low Power Consump2on High 9/19/13 3

4 What Lives in the LiOle Red Box? Output (mv/g) Power (mw) (1) STJ- 3D (2) Ferreira (3) Zeng (4) Sanchez (5) Breth* (6a) Yin (concentrator) (6b) Yin (no conc.) (7) Honeywell AMR (8) E. S. Leland Sensor Our Target 1. Micro- Magne2cs STJ- 3D (Commercial $800 sensor) 2. Ferreira et al, IEEE Transac*ons on Magne*cs, vol 48, pp , Zeng et al, Applied Physics Le8ers, vol 101, , Sanchez et al, IEEE Transac*ons on Magne*cs, vol 48, pp , Breth et al, IEEE Transac*ons on Magne*cs, vol 47, pp , *( Requires precision current source not included in power budget) 6. Yin and Liou, 2012 IEEE Sensors, pp 1-4, (Required a high- quality low- noise amplifier to measure) 7. Honeywell HMC104x series 9/19/13 (per axis, normalized to 1v) 8. Eli Leland s thesis work (piezoelectric magne2c) 9. Targeted range for this sensor 4

5 How Does Our Sensor Work? Proximity- based Uses gradient Flowing charge magne2c field force strain flowing charge Sensor is self- powered (only ref. circuitry needs power) y x microscale permanent magnet appliance power cord (cross-section) piezoelectric MEMS cantilever output voltage A MEMS Current Sensor 9/19/13 5

6 When is a Sensor Not (Just) a Sensor? Large scale Piezoelectric Produces lots of charge Load doesn t maoer (much) for sensing V out 9/19/13 6

7 When is a Sensor Not (Just) a Sensor? Small scale Less material, less charge Suddenly, load maoers Behaves like energy harvester V out 9/19/13 7

8 A Sensor That Thinks it s a Harvester Sensor needs a reference load (R amp ) and must be tuned for this. Vary device length, width, electrode coverage, and magnet size I out R amp + AMP - V out 9/19/13 8

9 Op2mizing? Aim for the Sweet Spot Limited energy/bandwidth target harmonics Target device f n that gives most uniform response to harmonics 9/19/13 9

10 Next, Op2mize for Dynamic Range 9/19/13 10

11 But What About Material Selec2on? PZT (Lead Zirconate Titanate) AlN (Aluminum Nitride) Sensi2vity (mv/a) Resonant Frequency (Hz) Dynamic Range (db) Ref. Resistor (Megohms) Device Length (microns) Device Width (microns) Electrode Length (microns) Magnet Size (microns) AlN gives beoer raw output, but Requires 9x more die space Requires a really large (100 Megohm!) resistor Has less dynamic range PZT has other issues (contains lead) but gives beoer Dynamic Range and is easier to instrument Proceeding with PZT for now, but not ruling AlN out 9/19/13 11

12 Our Layer Stack Made up of thin films on standard SOI wafer Piezoelectric PZT between Ti- Pt (lower electrode) and Cr- Au (upper electrode) Uses a booom- mounted magnet Key Upper Electrode PZT Solgel Lower Electrode Silicon Oxide Silicon Magnet 9/19/13 12

13 BeOer, Stronger Magnets Pile of cannonballs magnet Bulk cube magnets Bulk, plated, N52- grade Neodymium Iron Boron cube magnets Large enough for pick and place (850um) Generally more consistent than previous version magnets 9/19/13 13

14 Recent Results for PZT Appear to be spinning good films Rela2vely consistent thickness across center 8cm of wafer Mirrorlike solgel film 9/19/13 14

15 PZT (closeup) Film thickness about as expected (85-90nm/layer) PZT displays epitaxial growth (good) 260.1nm 204.5nm SEM image of film cross- sec2on (Courtesy Seth Fortuna) 9/19/13 15

16 Top Electrode Deposi2on Target: 15nm Cr, 100nm Au Actual (measured): nm total Cr- Au electrodes on a bare wafer 9/19/13 16

17 BoOom Electrode Etch Argon milling done on Nanolab Ionmill Physical bombardment bead blas2ng with atoms Process limited to 10cm (4 ) wafers Ionmill pump, chamber, and gun assembly Ionmill controls 9/19/13 17

18 Near- Final Wafer Process coming together. Wafer includes Current sensors Energy harvesters Voltage test structures Test capacitors Further process refinements in progress Process wafer (pre- silicon etch/release) 9/19/13 18