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Device level vacuum packaged micromachined infrared detectors on flexible substrates Aamer Mahmood Donald P. Butler Zeynep Çelik-Butler Microsensors Laboratory.

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Presentation on theme: "Device level vacuum packaged micromachined infrared detectors on flexible substrates Aamer Mahmood Donald P. Butler Zeynep Çelik-Butler Microsensors Laboratory."— 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 2 Outline  Microbolometers Flexible substrates  Device level vacuum packaging Design and fabrication  Characterization  Future work

3 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, G eff = thermal conductivity

4 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 5 Microbolometer fabrication Trench Geometry (Not to scale)

6 6 Fabrication (Silicon wafer)

7 7 Fabrication (PI 5878G)

8 8 Fabrication (Nitride)

9 9 Fabrication (Al)

10 10 Fabrication (Sacrificial Polyimide PI 2610)

11 11 Fabrication (Support Nitride)

12 12 Fabrication (Ti arms)

13 13 Fabrication (Au contacts)

14 14 Fabrication (YBCO detector pixel)

15 15 Fabrication (Photodefinable PI2737 sacrificial mesa)

16 16 Fabrication (Al 2 O 3 )

17 17 Section of vacuum cavity before micromachining Al 2 O 3 Sacrificial PI2737 mesa Sacrificial PI2610 Al mirror Nitride

18 18 Fabrication (Partially micromachined)

19 19 Fabrication (Fully micromachined)

20 20 Fabrication (Sealed vacuum cavity)

21 21 Fabrication (Superstrate PI 5878G)

22 22 Single microbolometer

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

24 24 Structural integrity of vacuum element

25 25 Al 2 O 3 stress analysis

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

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

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

29 29 VI curve G th =3.36x10 -6 W/K

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

31 31 Current Responsivity (R I ) R I =6.13x Hz Current Responsivity (R I ) =Output current/Input power

32 32 Detectivity (D*) D* = 1.76x10 5 cm-Hz 1/2 /W Detectivity = D* = Area normalized signal to noise ratio

33 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 R I is 6.13x10 -5 A/W, D*=1.76x10 5 cm- Hz 1/2 /W

34 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 35  This work is supported by the National Science Foundation  ECS The End


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