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Aamer Mahmood Donald P. Butler Zeynep Çelik-Butler

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Presentation on theme: "Aamer Mahmood Donald P. Butler Zeynep Çelik-Butler"— Presentation transcript:

1 Device level vacuum packaged micromachined infrared detectors on flexible substrates
Aamer Mahmood Donald P. Butler Zeynep Çelik-Butler Microsensors Laboratory Department of Electrical Engineering University of Texas at Arlington, Arlington, TX 76019

2 Outline Microbolometers Device level vacuum packaging Characterization
Flexible substrates Device level vacuum packaging Design and fabrication Characterization Future work

3 Bolometers Bolometers are thermal detectors
YBCO is used as the detector material Change in temperature induces a change in the detector resistance η = absorptivity, β = TCR,  = angular frequency of incident radiation, τ = detector thermal time constant, ΔΦ = the magnitude of the incident flux fluctuation, Geff = thermal conductivity

4 Sensors on flexible substrates
PI 5878G (liquid Kapton) is used as the flexible substrate Sensor Arrays on flexible substrates (Smart skins) Infrared sensors Pressure/Tactile Sensors Flow sensors Humidity sensors Velocity sensors Accelerometers Advantages of flexible substrate micro sensors Low cost Lightweight Conformable to non planar surfaces High degree of redundancy Vacuum packaging brings the best out of many MEMS devices

5 Microbolometer fabrication
Trench Geometry (Not to scale)

6 Fabrication (Silicon wafer)

7 Fabrication (PI 5878G)

8 Fabrication (Nitride)

9 Fabrication (Al)

10 Fabrication (Sacrificial Polyimide PI 2610)

11 Fabrication (Support Nitride)

12 Fabrication (Ti arms)

13 Fabrication (Au contacts)

14 Fabrication (YBCO detector pixel)

15 Fabrication (Photodefinable PI2737 sacrificial mesa)

16 Fabrication (Al2O3)

17 Section of vacuum cavity before micromachining
Al2O3 Sacrificial PI2737 mesa Nitride Al mirror Sacrificial PI2610 Nitride

18 Fabrication (Partially micromachined)

19 Fabrication (Fully micromachined)

20 Fabrication (Sealed vacuum cavity)

21 Fabrication (Superstrate PI 5878G)

22 Single microbolometer

23 Design considerations
Transmission through optical window Structural integrity of vacuum element Lateral dimensions Cavity resonant wavelength Axial dimensions

24 Structural integrity of vacuum element

25 Al2O3 stress analysis

26 Thermal analysis Gth ≈ 5x10-6 W/K (Vacuum) ≈10-4 W/K (air)

27 Fabrication of encapsulated devices
Fully micromachined device Partially micromachined device SEM graph of an unsealed micromachined device

28 Fabrication of encapsulated devices
Vacuum cavity SEM graph of sealed device Sealed device SEM graph of cross section of vacuum cavity

29 VI curve Gth=3.36x10-6 W/K

30 Temperature Coefficient of Resistance (TCR)
R(300K)=53.4 MΩ TCR(300K)=-3.4%/K

31 Current Responsivity (RI)
=Output current/Input power RI=6.13x10-5 A/W @ 5Hz

32 Detectivity (D*) Detectivity = D*
= Area normalized signal to noise ratio D* = 1.76x105 cm-Hz1/2/W

33 Conclusion Device level vacuum encapsulated microbolometers on flexible substrates have been fabricated Theoretical thermal conductivity in vacuum is 5x10-6 W/K Measured thermal conductivity is 3.36x10-6 W/K (Intact Vacuum cavity) Measured room temperature TCR is -3.4%/K, resistance is 53.4MΩ Measured RI is 6.13x10-5 A/W, D*=1.76x105cm-Hz1/2/W

34 Future work Incorporating more sensors in the smart skins e.g. pressure/tactile sensors, flow sensors, accelerometers Cavity design to improve/tune optical response True integrated flexible system

35 This work is supported by the National Science Foundation
ECS The End

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