Development Of Polymer-Based Artificial Haircell ... - Semantic Scholar
3B2.3
DEVELOPMENT OF POLYMER-BASED ARTIFICIAL HAIRCELL USING SURFACE MICROMACHINING AND 3D ASSEMBLY Jack Chen, Jonathan Engel, and Chang Liu Micro Actuator, Sensor, and System Research Group (MASS) Department of Electrical and Computer Engineering, University of Illinois at Urbana-Champaign 208 N. Wright St., Urbana, IL 61801
Abstract We report the development of an artificial haircell (AHC) fabricated using polymer surface micromachining and efficient 3D assembly. The AHC is modeled after biological hair cells, a common and versatile mechanoreceptor in biology. The design and fabrication process are discussed in the paper. Response to static deflection and airflow is also discussed.
Introduction Insects and fish use clusters of hair cells to monitor air [1] or water flow [2]. A hair cell consists of a cilium attached to a nerve cell. When the cilium of the hair cell is bent by fluid flow, the displacement will induce output responses from the attached nerve cell. Flow sensors based on cantilevers have been studied in the past to measure fluid flow. These can be broadly categorized as artificial haircell sensors. There are two types of artificial hair cells. The first type has a cilium (often called a cantilever or paddle) that is parallel to the substrate, and is sensitive to flow and forces that act normal to the substrate [3,4]. For this type of AHC, the cantilever extends out of the substrate and has an integrated resistive strain gauge at the base. AHC made with such configuration is relatively simple to fabricate but it is difficult to integrate and package into a useful 2D arrangement. To achieve a 2D array, multiple 1D arrays, each with their own handle (substrate), have to be wired together and packaged so that each chip is parallel to one another. A second type of AHC has a cilium that protrudes normal to substrate. To achieve this, several ideas have been considered. For example, sensors have been fabricated by manually attaching thin wires as the vertical cilium to measure bi-directional airflow [3]; however, this process is tedious and non-repeatable. Another group fabricated an array of switches integrated with vertical cilium [5]. This method can measure incremental increase in flow rate by designing the cilium geometry to trigger the switch at different flow rates. However, the cilium is bent individually into an upright position by manual probing, which is just as tedious and slow. Recently, our group has used silicon bulk machining in conjunction with 3D
assembly to realize an integrated artificial haircell sensor to measure water flow [6]. What all these devices have in common is the need to use silicon substrates and high processing temperature. This is undesirable because the silicon is brittle and cannot be made into a large, distributed array cheaply. Recently, some groups have tried to integrate metal strain gauges onto polymer beams [7], similar to commercial strain gauges that are typically made of a low TCR metal alloy adhering to a polyimide film. Such metal thin-film strain gauges are more robust and easier to fabricate because silicon is not needed as the starting material, but at the expense of sensitivity. They typically have a gauge factor around 2, compared to single crystal silicon that can have a gauge factor of over 100. In this work, we realized artificial haircells using polymer material and efficient 3D assembly [8] (PDMA) to increase mechanical robustness, reduce footprint, and potentially lower costs. Major contributions of our work include the following: (1) The sensor is built using a low-temperature microfabrication process and surface micromachining, making it suitable for a variety of substrates including silicon, glass, and polymer materials. Polymer substrate is flexible and can be mounted on curved surfaces; (2) Polymer based sensor is more mechanically robust than silicon counterparts; (3) The efficient process allows many such sensors to be made in parallel and with different directional sensitivities.
Device Overview The schematic of the AHC we fabricated is shown in Figure 1. The AHC is composed of a vertical beam (artificial cilium) rigidly attached to the substrate. Attached at the base of the beam, between the cilium and the substrate, is a strain gauge. The strain gauge is comprised of a thin film nichrome (NiCr) resistor sandwiched between a thick polyimide film that serves as a backing and a thinner film that protects the strain gauge. The polyimide films run the length of the entire cilium. When an external force is applied to the vertical beam, either through direct contact with another object
TRANSDUCERS ‘03 The 12th International Conference on Solid State Sensors, Actuators and Microsystems, Boston, June 8-12, 2003
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3B2.3 (functioning as a tactile sensor) or by the drag force from fluid flow (flow sensing), the beam will deflect and cause the strain gauge to stretch or compress. The strain gauge region is treated as being rigidly attached to the substrate, while the cilium is free. The magnitude of the induced strain (ε) is largest at the base, where the strain gauge is located,
ε=
Mc EI
(1)
where M is the moment experienced at the base, c is the distance between strain gauge and centerline, E and I are the modulus of elasticity of and the moment of inertia of the polyimide. The very thin nichrome resistor is not taken into account.
temperature used in the process. Afterwards, a 750-Å-thick NiCr layer used for the strain gauge is deposited by electron beam evaporation. This is followed by a 0.5-µm-thick Au/Cr evaporation used for electrical leads and the bending hinge. The Au/Cr layer is then used as a seed layer to electroplated approximately 5 µm of Permalloy before being removed by lift-off. The resulting structure is shown in Figure 2a. The final surface micromachining step is to pattern another 1.8-µm polyimide film to serve as a protective coating for the permalloy cilium and the NiCr strain gauge.
(a)
There are two novel aspects of fabrication compared to earlier work by others and our group. First, the vertical cilium is made of a stiff permalloy plating. Second, the strain gauge is integrated to the vertical cilium itself. Lastly, the cilium is actuated using an efficient 3D assembly and can be conducted on wafer scale.
Al PI NiCr Cr/Au Permalloy Hinge Ni
Celium
(b)
Strain gauge on Polyimide film
lc
Rigid metal support
Figure 2 Schematic of the fabrication process: (a) after depositing a Al sacrificial layer, polyimide support, NiCr strain gauge, Au lead, permalloy cilium, and a final polyimide protective coating; (b) after sacrificial layer etching and PDMA process.
M
The Al sacrificial layer is then etched in a basic solution for over a day to free the structure. The sample is then carefully rinsed and placed in the electroplating bath, where an external magnetic field is applied which interacts with the Permalloy to raise the cilium out of plane.
Nickel anode
Figure 1 Schematic of an artificial hair cell (top polyimide layer not drawn). The vertical part is surface micromachined and deflected out of plane using magnetic 3D assembly. The vertical portion will remain in deflected position due to plastic deformation at the joint.
i
probe i
External Magnetic Field
Fabrication The fabrication comprises of a series of metallization and polymer deposition steps. First, a 0.5-µm Al sacrificial layer is evaporated and patterned onto the substrate. Then, a 5.8-µm photodefinable polyimide (HD-4000 from HD Microsystems) is spun-on and patterned photolithographically. The polyimide is cured at 350°C in a 1 Torr N2 vacuum for 2 hours. This is the highest
Electromagnet Figure 3 Post-release Ni plating setup. External magnetic field is applied with the electromagnet during the electroplating process. The entire process is done under a microscope. After a few minutes of plating, the magnetic field can be removed and the cilium will remain permanently out of plane.
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3B2.3 While the external field is being applied, we electroplate Ni on the Au hinge, which rigidly fixes the structure out-ofplane to the substrate and reinforces the ductile Au hinge, as shown in Figure 3. The nickel electroplates all the AHCs on the chip at the same time though electrical leads that connects all the hinges. The overall plating process lasts about 20 minutes to achieve a thickness of approximately 10 µm. The actual thickness is difficult to measure and control, but is not important as long as it is rigid relative to the polyimide film. SEM image of the hinge is shown in Figure 4, showing the difference between a deformed Au hinge with and without Ni plating. An array of AHC with different cilium and strain gauge geometry is shown in Figure 5, showing the parallel nature of the fabrication process. Overall, the fabrication method does not exceed temperature over 350 deg Celsius, allowing it to be completed on a skin-like thin film polymer substrate. Silicon, glass, and Kapton film have all been used as a substrate for this process. The resistances of the various devices tested range from 1.2kΩ to 3.2kΩ, TCR measurement of the as-deposited NiCr film has a value of –25ppm/°C, which is very small and should not contribute significant anemometric effects during airflow measurement.
(a)
Experimental Results The resistance change due to displacement is shown in Figure 6 for two AHCs with different cilium length (lc). A micromanipulator is used to deflect the distal end of the vertical cilium. The resistance change is measured by a multimeter, and is linear to the beam deflection. The gauge factor GF can be calculated from the slope of the curve,
GF =
dR R
(2)
ε PI
where dR/R is the percent resistance change, and εPI is the strain experienced by the strain gauge. x = l c sin θ (3) Referring to the embedded schematic in Figure 6, given an input displacement x, θ is the calculated using (3) assuming that the cilium (lc) is rigid. This deflection angle (θ) is related to strain using the fixed-free beam deflection equation over the soft strain gauge portion (lPI). The deflection in the small polyimide section is ignored when calculating the angle. The plastically deformed hinge, after being plated with approximately 10 µm of Ni, is very rigid. The modulus of elasticity for the nickel is approximately two orders of magnitude larger than polyimide (200 GPa versus 3.5 GPa). Therefore, the assumption of a fixed-free cantilever model should be valid. The measured gauge factor for our strain gauge configuration is about 0.8, which is lower than expected. This could be attributed to the strain gauge not being located at the point of maximum strain.
(b)
1800
Resistance change (ppm)
Figure 4 SEM of the plastically deformed Au hinge (a) without and (b) with nickel electroplating.
1600 1400
l c =1000µm
1200
l c =1500µm
1000 800 600
x
400
θ
lPI
lc
200 0 0
Strain Gauge
50
100 150 200 Cilium deflection, x (mm)
250
Figure 6 Resistance change versus deflection for 1500 µm and 1000 µm long and 200 µm wide cilium. lPI is 130 µm for both beams.
Cilium
Figure 5 SEM of a fabricated hair cell array with different heights and widths. Fabricated device has cilium length varying from 600µm to 1.5mm. The strain gauge is not apparent because of the top protective polyimide coating.
Several of the fabricated haircells are then tested as airflow transducers in a wind tunnel. The airflow with velocity U impinging on the cilium results in a drag force acting normal to the paddle, leading to a moment on the strain gauge
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3B2.3 l
M = ³ C D 12 ρU 2 wydy
Conclusion
(4)
o
where CD is the drag coefficient, ρ is the density of air, w and l are the width and length of the cilium. Because strain is proportional to the applied moment, and resistance change is proportional to strain, Equation (4) above suggests a quadratic relationship between airflow and resistance change. In addition, by systematically varying the height and width of the cilium, we can tailor the response to different range of air velocity. The polarity of resistance change is dependant on the direction of the airflow. The wind tunnel measurement of three AHC with different cilium geometry is plotted in Figure 7. The devices tested were fabricated on silicon substrate to allow wire bonding to the sample. The device with the longest cilium length of 1500µm is the most sensitive, with dR/R reaching 600ppm at around 10 m/s. The device with the shortest cilium, even with a wider width, does not have the 600ppm resistance change until 30m/s. The sign of resistance change can be indicative of the direction of air velocity. However, the response in various directions does not seem to be symmetrical. This is because it is difficult for the PDMA assembly process to orient the cilium at exactly 90° to the substrate.
Resistance change (ppm)
800
L=1000, W=200µ m L=1000, W=150µ m L=1500, W=100µ m
600 400 200 0 -200 -400 -600 -800 -30
-20
-10
0
10
20
30
Air velocity (m/s)
Figure 7 Airflow response of AHC inside wind tunnel. AHC with various cilium width and lengths are measured. The velocity response can be tailored by changing the cilium geometry.
We have developed a surface micromachined artificial haircell for flow sensing applications. The cilium of the AHC is oriented normal to the substrate using a threedimensional assembly technique. The fabrication process works on a variety of substrates, and can potentially be made on a large flexible polymer “skin”.
Acknowledgments This material is based upon work supported by the National Science Foundation under Grant No. NSF IIS 99-84954 (Liu CAREER Grant) and Grant No. NSF IIS 00-80639 (NSF Sensitive Skin program, and by the AFOSR BioInspired Concept Program.
References [1] T. Friedel, F. G. Barth, “Wind-sensitive interneurones in the spider CNS,” J. Comp. Physiology A, vol. 180, 1997, pp. 223-233. [2] C. E. Bond, 1996 Biology of Fishes 2nd ed (Philadelphia, PA: Saunders). [3] Y. Ozaki, T. Ohyama, T. Yasuda, I. Shimoyama, “An air flow sensor modeled on wind receptor hairs of insects”, Proc. MEMS 2000, pp. 531-6, Miyazaki, Japan. [4] Y. Su, et al, “Characterization of a highly sensitive ultrathin piezoresistive silicon cantilever probe and its application in gas flow velocity sensing,” Journal of Micromechanics and Microengineering, vol. 12, 2002, pp. 780-785. [5] T. G. Barnes, T. Q. Truong, X. Lu, N. E. McGruer, G. G. Adams, “Design, Analysis, Fabrication, and Testing of a MEMS Flow Sensor,” 1999 ASME International Congress and Exposition on MEMS, vol. 1, 1999, pp. 355-361. [6] Z. Fan, J. Chen, J. Zou, D. Bullen, C. Liu, F. Delcomyn, "Design and Fabrication of Artificial Lateral-Line Flow Sensors," Journal of Micromechanics and Microengineering, Vol. 12, No. 5, pp. 655-661, September 2002. [7] J. Thaysen, et al, “Polymer-based stress sensor with integrated readout,” Journal of Physics D – Applied Physics, vol. 35, no. 21, November 2002, pp. 2698-2703. [8] J. Zou, J. Chen, C. Liu, and J. Schutt-Aine, "Plastic Deformation Magnetic Assembly (PDMA) of Out-Of-Plane Microstructures: Technology and Application," J. of Microelectromechanical Systems, 10 (2), pp. 302-309, June 2001.
TRANSDUCERS ‘03 The 12th International Conference on Solid State Sensors, Actuators and Microsystems, Boston, June 8-12, 2003
0-7803-7731-1/03/$17.00 ©2003 IEEE
1038
DEVELOPMENT OF POLYMER-BASED ARTIFICIAL HAIRCELL USING SURFACE MICROMACHINING AND 3D ASSEMBLY Jack Chen, Jonathan Engel, and Chang Liu Micro Actuator, Sensor, and System Research Group (MASS) Department of Electrical and Computer Engineering, University of Illinois at Urbana-Champaign 208 N. Wright St., Urbana, IL 61801
Abstract We report the development of an artificial haircell (AHC) fabricated using polymer surface micromachining and efficient 3D assembly. The AHC is modeled after biological hair cells, a common and versatile mechanoreceptor in biology. The design and fabrication process are discussed in the paper. Response to static deflection and airflow is also discussed.
Introduction Insects and fish use clusters of hair cells to monitor air [1] or water flow [2]. A hair cell consists of a cilium attached to a nerve cell. When the cilium of the hair cell is bent by fluid flow, the displacement will induce output responses from the attached nerve cell. Flow sensors based on cantilevers have been studied in the past to measure fluid flow. These can be broadly categorized as artificial haircell sensors. There are two types of artificial hair cells. The first type has a cilium (often called a cantilever or paddle) that is parallel to the substrate, and is sensitive to flow and forces that act normal to the substrate [3,4]. For this type of AHC, the cantilever extends out of the substrate and has an integrated resistive strain gauge at the base. AHC made with such configuration is relatively simple to fabricate but it is difficult to integrate and package into a useful 2D arrangement. To achieve a 2D array, multiple 1D arrays, each with their own handle (substrate), have to be wired together and packaged so that each chip is parallel to one another. A second type of AHC has a cilium that protrudes normal to substrate. To achieve this, several ideas have been considered. For example, sensors have been fabricated by manually attaching thin wires as the vertical cilium to measure bi-directional airflow [3]; however, this process is tedious and non-repeatable. Another group fabricated an array of switches integrated with vertical cilium [5]. This method can measure incremental increase in flow rate by designing the cilium geometry to trigger the switch at different flow rates. However, the cilium is bent individually into an upright position by manual probing, which is just as tedious and slow. Recently, our group has used silicon bulk machining in conjunction with 3D
assembly to realize an integrated artificial haircell sensor to measure water flow [6]. What all these devices have in common is the need to use silicon substrates and high processing temperature. This is undesirable because the silicon is brittle and cannot be made into a large, distributed array cheaply. Recently, some groups have tried to integrate metal strain gauges onto polymer beams [7], similar to commercial strain gauges that are typically made of a low TCR metal alloy adhering to a polyimide film. Such metal thin-film strain gauges are more robust and easier to fabricate because silicon is not needed as the starting material, but at the expense of sensitivity. They typically have a gauge factor around 2, compared to single crystal silicon that can have a gauge factor of over 100. In this work, we realized artificial haircells using polymer material and efficient 3D assembly [8] (PDMA) to increase mechanical robustness, reduce footprint, and potentially lower costs. Major contributions of our work include the following: (1) The sensor is built using a low-temperature microfabrication process and surface micromachining, making it suitable for a variety of substrates including silicon, glass, and polymer materials. Polymer substrate is flexible and can be mounted on curved surfaces; (2) Polymer based sensor is more mechanically robust than silicon counterparts; (3) The efficient process allows many such sensors to be made in parallel and with different directional sensitivities.
Device Overview The schematic of the AHC we fabricated is shown in Figure 1. The AHC is composed of a vertical beam (artificial cilium) rigidly attached to the substrate. Attached at the base of the beam, between the cilium and the substrate, is a strain gauge. The strain gauge is comprised of a thin film nichrome (NiCr) resistor sandwiched between a thick polyimide film that serves as a backing and a thinner film that protects the strain gauge. The polyimide films run the length of the entire cilium. When an external force is applied to the vertical beam, either through direct contact with another object
TRANSDUCERS ‘03 The 12th International Conference on Solid State Sensors, Actuators and Microsystems, Boston, June 8-12, 2003
0-7803-7731-1/03/$17.00 ©2003 IEEE
1035
3B2.3 (functioning as a tactile sensor) or by the drag force from fluid flow (flow sensing), the beam will deflect and cause the strain gauge to stretch or compress. The strain gauge region is treated as being rigidly attached to the substrate, while the cilium is free. The magnitude of the induced strain (ε) is largest at the base, where the strain gauge is located,
ε=
Mc EI
(1)
where M is the moment experienced at the base, c is the distance between strain gauge and centerline, E and I are the modulus of elasticity of and the moment of inertia of the polyimide. The very thin nichrome resistor is not taken into account.
temperature used in the process. Afterwards, a 750-Å-thick NiCr layer used for the strain gauge is deposited by electron beam evaporation. This is followed by a 0.5-µm-thick Au/Cr evaporation used for electrical leads and the bending hinge. The Au/Cr layer is then used as a seed layer to electroplated approximately 5 µm of Permalloy before being removed by lift-off. The resulting structure is shown in Figure 2a. The final surface micromachining step is to pattern another 1.8-µm polyimide film to serve as a protective coating for the permalloy cilium and the NiCr strain gauge.
(a)
There are two novel aspects of fabrication compared to earlier work by others and our group. First, the vertical cilium is made of a stiff permalloy plating. Second, the strain gauge is integrated to the vertical cilium itself. Lastly, the cilium is actuated using an efficient 3D assembly and can be conducted on wafer scale.
Al PI NiCr Cr/Au Permalloy Hinge Ni
Celium
(b)
Strain gauge on Polyimide film
lc
Rigid metal support
Figure 2 Schematic of the fabrication process: (a) after depositing a Al sacrificial layer, polyimide support, NiCr strain gauge, Au lead, permalloy cilium, and a final polyimide protective coating; (b) after sacrificial layer etching and PDMA process.
M
The Al sacrificial layer is then etched in a basic solution for over a day to free the structure. The sample is then carefully rinsed and placed in the electroplating bath, where an external magnetic field is applied which interacts with the Permalloy to raise the cilium out of plane.
Nickel anode
Figure 1 Schematic of an artificial hair cell (top polyimide layer not drawn). The vertical part is surface micromachined and deflected out of plane using magnetic 3D assembly. The vertical portion will remain in deflected position due to plastic deformation at the joint.
i
probe i
External Magnetic Field
Fabrication The fabrication comprises of a series of metallization and polymer deposition steps. First, a 0.5-µm Al sacrificial layer is evaporated and patterned onto the substrate. Then, a 5.8-µm photodefinable polyimide (HD-4000 from HD Microsystems) is spun-on and patterned photolithographically. The polyimide is cured at 350°C in a 1 Torr N2 vacuum for 2 hours. This is the highest
Electromagnet Figure 3 Post-release Ni plating setup. External magnetic field is applied with the electromagnet during the electroplating process. The entire process is done under a microscope. After a few minutes of plating, the magnetic field can be removed and the cilium will remain permanently out of plane.
TRANSDUCERS ‘03 The 12th International Conference on Solid State Sensors, Actuators and Microsystems, Boston, June 8-12, 2003
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3B2.3 While the external field is being applied, we electroplate Ni on the Au hinge, which rigidly fixes the structure out-ofplane to the substrate and reinforces the ductile Au hinge, as shown in Figure 3. The nickel electroplates all the AHCs on the chip at the same time though electrical leads that connects all the hinges. The overall plating process lasts about 20 minutes to achieve a thickness of approximately 10 µm. The actual thickness is difficult to measure and control, but is not important as long as it is rigid relative to the polyimide film. SEM image of the hinge is shown in Figure 4, showing the difference between a deformed Au hinge with and without Ni plating. An array of AHC with different cilium and strain gauge geometry is shown in Figure 5, showing the parallel nature of the fabrication process. Overall, the fabrication method does not exceed temperature over 350 deg Celsius, allowing it to be completed on a skin-like thin film polymer substrate. Silicon, glass, and Kapton film have all been used as a substrate for this process. The resistances of the various devices tested range from 1.2kΩ to 3.2kΩ, TCR measurement of the as-deposited NiCr film has a value of –25ppm/°C, which is very small and should not contribute significant anemometric effects during airflow measurement.
(a)
Experimental Results The resistance change due to displacement is shown in Figure 6 for two AHCs with different cilium length (lc). A micromanipulator is used to deflect the distal end of the vertical cilium. The resistance change is measured by a multimeter, and is linear to the beam deflection. The gauge factor GF can be calculated from the slope of the curve,
GF =
dR R
(2)
ε PI
where dR/R is the percent resistance change, and εPI is the strain experienced by the strain gauge. x = l c sin θ (3) Referring to the embedded schematic in Figure 6, given an input displacement x, θ is the calculated using (3) assuming that the cilium (lc) is rigid. This deflection angle (θ) is related to strain using the fixed-free beam deflection equation over the soft strain gauge portion (lPI). The deflection in the small polyimide section is ignored when calculating the angle. The plastically deformed hinge, after being plated with approximately 10 µm of Ni, is very rigid. The modulus of elasticity for the nickel is approximately two orders of magnitude larger than polyimide (200 GPa versus 3.5 GPa). Therefore, the assumption of a fixed-free cantilever model should be valid. The measured gauge factor for our strain gauge configuration is about 0.8, which is lower than expected. This could be attributed to the strain gauge not being located at the point of maximum strain.
(b)
1800
Resistance change (ppm)
Figure 4 SEM of the plastically deformed Au hinge (a) without and (b) with nickel electroplating.
1600 1400
l c =1000µm
1200
l c =1500µm
1000 800 600
x
400
θ
lPI
lc
200 0 0
Strain Gauge
50
100 150 200 Cilium deflection, x (mm)
250
Figure 6 Resistance change versus deflection for 1500 µm and 1000 µm long and 200 µm wide cilium. lPI is 130 µm for both beams.
Cilium
Figure 5 SEM of a fabricated hair cell array with different heights and widths. Fabricated device has cilium length varying from 600µm to 1.5mm. The strain gauge is not apparent because of the top protective polyimide coating.
Several of the fabricated haircells are then tested as airflow transducers in a wind tunnel. The airflow with velocity U impinging on the cilium results in a drag force acting normal to the paddle, leading to a moment on the strain gauge
TRANSDUCERS ‘03 The 12th International Conference on Solid State Sensors, Actuators and Microsystems, Boston, June 8-12, 2003
0-7803-7731-1/03/$17.00 ©2003 IEEE
1037
3B2.3 l
M = ³ C D 12 ρU 2 wydy
Conclusion
(4)
o
where CD is the drag coefficient, ρ is the density of air, w and l are the width and length of the cilium. Because strain is proportional to the applied moment, and resistance change is proportional to strain, Equation (4) above suggests a quadratic relationship between airflow and resistance change. In addition, by systematically varying the height and width of the cilium, we can tailor the response to different range of air velocity. The polarity of resistance change is dependant on the direction of the airflow. The wind tunnel measurement of three AHC with different cilium geometry is plotted in Figure 7. The devices tested were fabricated on silicon substrate to allow wire bonding to the sample. The device with the longest cilium length of 1500µm is the most sensitive, with dR/R reaching 600ppm at around 10 m/s. The device with the shortest cilium, even with a wider width, does not have the 600ppm resistance change until 30m/s. The sign of resistance change can be indicative of the direction of air velocity. However, the response in various directions does not seem to be symmetrical. This is because it is difficult for the PDMA assembly process to orient the cilium at exactly 90° to the substrate.
Resistance change (ppm)
800
L=1000, W=200µ m L=1000, W=150µ m L=1500, W=100µ m
600 400 200 0 -200 -400 -600 -800 -30
-20
-10
0
10
20
30
Air velocity (m/s)
Figure 7 Airflow response of AHC inside wind tunnel. AHC with various cilium width and lengths are measured. The velocity response can be tailored by changing the cilium geometry.
We have developed a surface micromachined artificial haircell for flow sensing applications. The cilium of the AHC is oriented normal to the substrate using a threedimensional assembly technique. The fabrication process works on a variety of substrates, and can potentially be made on a large flexible polymer “skin”.
Acknowledgments This material is based upon work supported by the National Science Foundation under Grant No. NSF IIS 99-84954 (Liu CAREER Grant) and Grant No. NSF IIS 00-80639 (NSF Sensitive Skin program, and by the AFOSR BioInspired Concept Program.
References [1] T. Friedel, F. G. Barth, “Wind-sensitive interneurones in the spider CNS,” J. Comp. Physiology A, vol. 180, 1997, pp. 223-233. [2] C. E. Bond, 1996 Biology of Fishes 2nd ed (Philadelphia, PA: Saunders). [3] Y. Ozaki, T. Ohyama, T. Yasuda, I. Shimoyama, “An air flow sensor modeled on wind receptor hairs of insects”, Proc. MEMS 2000, pp. 531-6, Miyazaki, Japan. [4] Y. Su, et al, “Characterization of a highly sensitive ultrathin piezoresistive silicon cantilever probe and its application in gas flow velocity sensing,” Journal of Micromechanics and Microengineering, vol. 12, 2002, pp. 780-785. [5] T. G. Barnes, T. Q. Truong, X. Lu, N. E. McGruer, G. G. Adams, “Design, Analysis, Fabrication, and Testing of a MEMS Flow Sensor,” 1999 ASME International Congress and Exposition on MEMS, vol. 1, 1999, pp. 355-361. [6] Z. Fan, J. Chen, J. Zou, D. Bullen, C. Liu, F. Delcomyn, "Design and Fabrication of Artificial Lateral-Line Flow Sensors," Journal of Micromechanics and Microengineering, Vol. 12, No. 5, pp. 655-661, September 2002. [7] J. Thaysen, et al, “Polymer-based stress sensor with integrated readout,” Journal of Physics D – Applied Physics, vol. 35, no. 21, November 2002, pp. 2698-2703. [8] J. Zou, J. Chen, C. Liu, and J. Schutt-Aine, "Plastic Deformation Magnetic Assembly (PDMA) of Out-Of-Plane Microstructures: Technology and Application," J. of Microelectromechanical Systems, 10 (2), pp. 302-309, June 2001.
TRANSDUCERS ‘03 The 12th International Conference on Solid State Sensors, Actuators and Microsystems, Boston, June 8-12, 2003
0-7803-7731-1/03/$17.00 ©2003 IEEE
1038
