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Electrothermal microgrippers for pick-and-place operations
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Microelectronic Engineering 85 (2008) 1128–1130 www.elsevier.com/locate/mee
Electrothermal microgrippers for pick-and-place operations Karin. N. Andersen a,*, Kenneth Carlson a, Dirch H. Petersen a, Kristian Mølhave a, Volkmar Eichhorn b, Sergej Fatikow b, Peter Bøggild a a
MIC – Department of Micro and Nanotechnology, Technical University of Denmark, NanoDTU, DTU, Oersteds Plads Building 345E, 2800 Kgs. Lyngby, Denmark b Division Microrobotics and Control Engineering, University of Oldenburg, 26111 Oldenburg, Germany Received 5 October 2007; accepted 27 December 2007 Available online 18 January 2008
Abstract Manipulation of carbon nanotubes to assemble functional devices can be done inside a scanning electron microscope in which a suitable combination of visual resolution and sample space allows macroscale manipulators with micro- or nanoscale precision to be incorporated, yet monitored with nm-scale precision. The pick-and-place procedure can be done in several ways. We present here a monolithic electrothermal microgripper, and demonstrate pick-and-place of an as-grown carbon nanotube from a 2D array onto a scanning probe tip, as a first step towards a reliable and precise pick-and-place process for carbon nanotubes. Ó 2008 Elsevier B.V. All rights reserved. Keywords: Microgrippers; Nanomanipulation; Carbon nanotubes; Atomic force microscopy; Pick-and-place
1. Introduction Several groups have previously used microfabrication to make microgrippers for manipulation [1], and commercial vendors exist today, such as Nascatec and Zyvex. The concept of nanotweezers was first demonstrated by Kim and Lieber [2], who gripped nanowires and nanoparticles between two electrostatically biased carbon nanotubes (CNTs) attached to a glass capillary. A simple five-electrode microcantilever layout similar to [1] can be used to make submicron grippers capable of both opening and closing without applying a voltage directly between the actuators [3]. This type of gripper was used to demonstrate manipulation of silicon nanowires [4,5]. Here, we demonstrate a more mechanically stable, electrothermal asymmetric rib cage microgripper with high gripping force fabricated in doped silicon. Our aim is to pick a single CNT out of an ordered array. The advantages of such a ‘‘component bank” with well*
Corresponding author. Tel.: +45 4525 5759; fax: +45 4588 7762. E-mail address: [email protected] (Karin. N. Andersen).
0167-9317/$ - see front matter Ó 2008 Elsevier B.V. All rights reserved. doi:10.1016/j.mee.2007.12.080
defined positions of all the components, is that the CNT can be grown with great uniformity across a large area ultimately allowing the manipulation system to locate the CNT automatically. It also enables picking a single CNT without affecting other CNTs with the manipulation tool. The microgripper needs to be small and delicate enough to align to a CNT with a diameter in the 100 nm range, mechanically strong enough to detach the as-grown CNT from the surface and finally able to release the CNT again at the desired position. In this paper we present an electrothermal microgripper fabricated in silicon and demonstrate its use in practical nanomanipulation of CNTs. 2. Methods 2.1. Electrothermal microgripper The electrothermal microgripper presented here is fabricated in single crystalline h1 1 1i silicon. An example of a fabricated microgripper can be seen in Fig. 1. By passing an electrical current through the ribs, the Joule heating
Karin. N. Andersen et al. / Microelectronic Engineering 85 (2008) 1128–1130
Fig. 1. A SEM image of an electrothermal microgripper with one moving arm and one rigid arm for shear pulling the carbon nanotubes from the substrate.
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Fig. 2. A silicon microgripper is in contact with a single carbon nanotube in an array of carbon nanotubes.
causes the ribs to elongate, thereby pushing the wide central beam outwards. Due to the anchoring via the thin beam, the right flexible arm is forced to move sideways, thus closing the gap. The asymmetric layout with one flexible (right) and one rigid (left) end-effector facilitates controlled detachment of CNTs from their fixed position on the surface, since the rigid side arm provides a stable base against which the CNT can be pressed and held. It is predicted in [5] that shear pulling (lateral direction) is easier than tensile pulling (vertical direction), and the rigid part of the microgripper provides a stable base against which the CNT can be pressed when detaching it from the growth substrate. 2.2. Nanomanipulation setup The nanohandling station [6] is mounted inside the vacuum chamber of a scanning electron microscope (SEM). The nanohandling station, which can be adjusted into the focus of the SEM by operating the SEM stage itself, consists of two different manipulators for coarse and fine positioning of microgripper and CNT sample, respectively. The coarse positioning of the microgripper is done by using a three-axis Kleindiek micromanipulator equipped with a holder for the microgripper. The second manipulator is a Physik Instrument nanopositioning stage with three degrees of freedom carrying the CNT array. This manipulator has a travel range of 50 lm with a minimum step size of 1.5 nm and is used for the fine positioning of the CNT towards the microgripper. Once the microgripper is brought into the range of the nanopositioning stage, the micromanipulator remains at its position; only the nanopositioning stage is used for aligning the microgripper and the CNT array on the nanoscale. 3. Results 3.1. Electrothermal microgrippers Fig. 3 shows a graph with the deflection of the flexible beam of three different ARC microgripper as a function
Fig. 3. Deflection of the flexible arm of three different microgrippers versus applied current for nine different ARC microgrippers, measured using an optical tracking system.
of the applied current. Qualitatively, the behavior of the shown microgrippers is initially parabolic, while a more linear behavior is observed for large voltages. This parabolic response is also what can be expected to a first approximation as described in [7]. 3.2. Nanomanipulation Using the in-situ manipulation system, a CNT was picked from an ordered array (see Fig. 2) and placed on an atomic force microscopy (AFM) tip (Fig. 4). The pick-and-place operation was performed using a series of steps: (i) Firstly the microgripper is aligned to the z-plane of the CNT, which is made difficult due to the lack of depth perception in the SEM (Fig. 4.1). (ii) The end-effectors are moved on either side of the CNT. (iii) The microgripper is actuated, creating a firm mechanical contact to the CNT. (iv) Sideways (shear) pulling eventually breaks the CNT at the base (Fig. 4.2). (v) After moving the CNT to the AFM probe (Fig. 4.3), electron beam deposition [8] is used to fix the CNT to the probe (Fig. 4.4). (vi) By gently pushing the CNT with the endeffectors, it is checked that the CNT is firmly attached to the probe.
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Karin. N. Andersen et al. / Microelectronic Engineering 85 (2008) 1128–1130
Fig. 4. A series of pictures showing the pick-and-place operation of a carbon nanotube from an ordered array onto an AFM tip [9]. The carbon nanotube is glued onto the AFM tip by electron beam induced deposition of carbonaceous species.
carbon nanotube from a 2D array onto a scanning probe tip, as a first step towards a reliable and precise pick-andplace process for carbon nanotubes. Given the diameter of the manipulated structure, and the fact that it has been produced with PECVD, it is possible that the internal structure is more fibre-like. In this paper, we have however termed it nanotube. Nanomanipulation using microgrippers is a slow process in comparison with wafer-scale catalytically grown structures directly on the target device [10]. However, mechanical nanomanipulation offers a great deal of flexibility in terms of allowing a wide range of nanostructures with different sizes, shapes, and materials to be positioned onto target devices, without having to establish a large-scale manufacturing process in each case. In order to be able to handle even smaller nanostructures further refinement of the microgrippers has to be done. One way to do this is by reducing the overall size of the microgrippers by defining the end-effectors by electron beam lithography. Furthermore, treatment of the end-effectors with a non-stick coating could facilitate release of the picked nanostructures. Acknowledgments We would like to thank the Engineering Department at the University of Cambridge, United Kingdom for supplying arrays of vertical aligned carbon nanotubes. The project was supported by EU Grants NANOHAND (IP 034274) and NANORAC (STREP 013680).
Fig. 5. SEM images (left) of commercial and CNT-enhanced AFM tip. The middle image shows high-aspect ratio grooves for comparing the performance of the two types of AFM tips. AFM scans (right) using the commercial and the CNT-enhanced AFM tip.
The CNT-enhanced AFM probe was used to scan highaspect ratio features. A test sample was fabricated in silicon in which 2.5 lm deep and 570 nm wide grooves were etched. Fig. 5 compares AFM scans using a commercial pyramidal AFM probe and the CNT-enhanced AFM probe. It is clear that the modified AFM probe has resolved the width significantly better than the standard pyramid shaped AFM tips without the CNT extension, and provided a better if not perfect profile of the deep trenches. A more thorough description of this experiment can be found in [9]. 4. Conclusion We have presented a monolithic electrothermal microgripper, and demonstrated pick-and-place of an as-grown
References [1] C.J. Kim, A.P. Pisano, R.S. Muller, M.G. Lim, Sensors and Actuators A—Physical 33 (1992) 221–227. [2] P. Kim, C.M. Lieber, Science 286 (1999) 2148–2150. [3] P. Boggild, T.M. Hansen, C. Tanasa, F. Grey, Nanotechnology 12 (2001) 331–335. [4] K. Molhave, T.M. Hansen, D.N. Madsen, P. Boggild, Journal of Nanoscience and Nanotechnology 4 (2004) 279–282. [5] K. Mølhave, T. Wich, A. Kortschack, P. Bøggild, Journal of Nanotechnology 17 (2006) 2434–2441. [6] S. Fatikow, S. Kray, V. Eichhorn, S. Tautz, in: Development of a Nanohandling Robot Station for Nanocharacterization by an AFM Probe, IEEE Mediterranean Conference on Control and Automation (MED), Ancona, Italy, June 28–30, 2006, WEA4-4. [7] K. Molhave, O. Hansen, Journal of Micromechanics and Microengineering 15 (2005) 165–1270. [8] D.N. Madsen, K. Molhave, R. Mateiu, P. Boggild, A.M. Rasmussen, C.C. Appel, M. Brorson, C.J.H. Jacobsen, Journal of Nanotechnology 1 (2003) 335–338. [9] K. Carlson, K.N. Andersen, V. Eichhorn, D.H. Petersen, k. Mølhave, I.Y.Y. Bu, K.B.K. Teo, W.I. Milne, S. Fatikow, P. Bøggild, Journal of Nanotechnology 18 (2007) 345501–345508. [10] H. Liu, K. Chao, J. Han, M. Meyyappan, Nano Letters 4 (2004) 1301–1308.
Microelectronic Engineering 85 (2008) 1128–1130 www.elsevier.com/locate/mee
Electrothermal microgrippers for pick-and-place operations Karin. N. Andersen a,*, Kenneth Carlson a, Dirch H. Petersen a, Kristian Mølhave a, Volkmar Eichhorn b, Sergej Fatikow b, Peter Bøggild a a
MIC – Department of Micro and Nanotechnology, Technical University of Denmark, NanoDTU, DTU, Oersteds Plads Building 345E, 2800 Kgs. Lyngby, Denmark b Division Microrobotics and Control Engineering, University of Oldenburg, 26111 Oldenburg, Germany Received 5 October 2007; accepted 27 December 2007 Available online 18 January 2008
Abstract Manipulation of carbon nanotubes to assemble functional devices can be done inside a scanning electron microscope in which a suitable combination of visual resolution and sample space allows macroscale manipulators with micro- or nanoscale precision to be incorporated, yet monitored with nm-scale precision. The pick-and-place procedure can be done in several ways. We present here a monolithic electrothermal microgripper, and demonstrate pick-and-place of an as-grown carbon nanotube from a 2D array onto a scanning probe tip, as a first step towards a reliable and precise pick-and-place process for carbon nanotubes. Ó 2008 Elsevier B.V. All rights reserved. Keywords: Microgrippers; Nanomanipulation; Carbon nanotubes; Atomic force microscopy; Pick-and-place
1. Introduction Several groups have previously used microfabrication to make microgrippers for manipulation [1], and commercial vendors exist today, such as Nascatec and Zyvex. The concept of nanotweezers was first demonstrated by Kim and Lieber [2], who gripped nanowires and nanoparticles between two electrostatically biased carbon nanotubes (CNTs) attached to a glass capillary. A simple five-electrode microcantilever layout similar to [1] can be used to make submicron grippers capable of both opening and closing without applying a voltage directly between the actuators [3]. This type of gripper was used to demonstrate manipulation of silicon nanowires [4,5]. Here, we demonstrate a more mechanically stable, electrothermal asymmetric rib cage microgripper with high gripping force fabricated in doped silicon. Our aim is to pick a single CNT out of an ordered array. The advantages of such a ‘‘component bank” with well*
Corresponding author. Tel.: +45 4525 5759; fax: +45 4588 7762. E-mail address: [email protected] (Karin. N. Andersen).
0167-9317/$ - see front matter Ó 2008 Elsevier B.V. All rights reserved. doi:10.1016/j.mee.2007.12.080
defined positions of all the components, is that the CNT can be grown with great uniformity across a large area ultimately allowing the manipulation system to locate the CNT automatically. It also enables picking a single CNT without affecting other CNTs with the manipulation tool. The microgripper needs to be small and delicate enough to align to a CNT with a diameter in the 100 nm range, mechanically strong enough to detach the as-grown CNT from the surface and finally able to release the CNT again at the desired position. In this paper we present an electrothermal microgripper fabricated in silicon and demonstrate its use in practical nanomanipulation of CNTs. 2. Methods 2.1. Electrothermal microgripper The electrothermal microgripper presented here is fabricated in single crystalline h1 1 1i silicon. An example of a fabricated microgripper can be seen in Fig. 1. By passing an electrical current through the ribs, the Joule heating
Karin. N. Andersen et al. / Microelectronic Engineering 85 (2008) 1128–1130
Fig. 1. A SEM image of an electrothermal microgripper with one moving arm and one rigid arm for shear pulling the carbon nanotubes from the substrate.
1129
Fig. 2. A silicon microgripper is in contact with a single carbon nanotube in an array of carbon nanotubes.
causes the ribs to elongate, thereby pushing the wide central beam outwards. Due to the anchoring via the thin beam, the right flexible arm is forced to move sideways, thus closing the gap. The asymmetric layout with one flexible (right) and one rigid (left) end-effector facilitates controlled detachment of CNTs from their fixed position on the surface, since the rigid side arm provides a stable base against which the CNT can be pressed and held. It is predicted in [5] that shear pulling (lateral direction) is easier than tensile pulling (vertical direction), and the rigid part of the microgripper provides a stable base against which the CNT can be pressed when detaching it from the growth substrate. 2.2. Nanomanipulation setup The nanohandling station [6] is mounted inside the vacuum chamber of a scanning electron microscope (SEM). The nanohandling station, which can be adjusted into the focus of the SEM by operating the SEM stage itself, consists of two different manipulators for coarse and fine positioning of microgripper and CNT sample, respectively. The coarse positioning of the microgripper is done by using a three-axis Kleindiek micromanipulator equipped with a holder for the microgripper. The second manipulator is a Physik Instrument nanopositioning stage with three degrees of freedom carrying the CNT array. This manipulator has a travel range of 50 lm with a minimum step size of 1.5 nm and is used for the fine positioning of the CNT towards the microgripper. Once the microgripper is brought into the range of the nanopositioning stage, the micromanipulator remains at its position; only the nanopositioning stage is used for aligning the microgripper and the CNT array on the nanoscale. 3. Results 3.1. Electrothermal microgrippers Fig. 3 shows a graph with the deflection of the flexible beam of three different ARC microgripper as a function
Fig. 3. Deflection of the flexible arm of three different microgrippers versus applied current for nine different ARC microgrippers, measured using an optical tracking system.
of the applied current. Qualitatively, the behavior of the shown microgrippers is initially parabolic, while a more linear behavior is observed for large voltages. This parabolic response is also what can be expected to a first approximation as described in [7]. 3.2. Nanomanipulation Using the in-situ manipulation system, a CNT was picked from an ordered array (see Fig. 2) and placed on an atomic force microscopy (AFM) tip (Fig. 4). The pick-and-place operation was performed using a series of steps: (i) Firstly the microgripper is aligned to the z-plane of the CNT, which is made difficult due to the lack of depth perception in the SEM (Fig. 4.1). (ii) The end-effectors are moved on either side of the CNT. (iii) The microgripper is actuated, creating a firm mechanical contact to the CNT. (iv) Sideways (shear) pulling eventually breaks the CNT at the base (Fig. 4.2). (v) After moving the CNT to the AFM probe (Fig. 4.3), electron beam deposition [8] is used to fix the CNT to the probe (Fig. 4.4). (vi) By gently pushing the CNT with the endeffectors, it is checked that the CNT is firmly attached to the probe.
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Karin. N. Andersen et al. / Microelectronic Engineering 85 (2008) 1128–1130
Fig. 4. A series of pictures showing the pick-and-place operation of a carbon nanotube from an ordered array onto an AFM tip [9]. The carbon nanotube is glued onto the AFM tip by electron beam induced deposition of carbonaceous species.
carbon nanotube from a 2D array onto a scanning probe tip, as a first step towards a reliable and precise pick-andplace process for carbon nanotubes. Given the diameter of the manipulated structure, and the fact that it has been produced with PECVD, it is possible that the internal structure is more fibre-like. In this paper, we have however termed it nanotube. Nanomanipulation using microgrippers is a slow process in comparison with wafer-scale catalytically grown structures directly on the target device [10]. However, mechanical nanomanipulation offers a great deal of flexibility in terms of allowing a wide range of nanostructures with different sizes, shapes, and materials to be positioned onto target devices, without having to establish a large-scale manufacturing process in each case. In order to be able to handle even smaller nanostructures further refinement of the microgrippers has to be done. One way to do this is by reducing the overall size of the microgrippers by defining the end-effectors by electron beam lithography. Furthermore, treatment of the end-effectors with a non-stick coating could facilitate release of the picked nanostructures. Acknowledgments We would like to thank the Engineering Department at the University of Cambridge, United Kingdom for supplying arrays of vertical aligned carbon nanotubes. The project was supported by EU Grants NANOHAND (IP 034274) and NANORAC (STREP 013680).
Fig. 5. SEM images (left) of commercial and CNT-enhanced AFM tip. The middle image shows high-aspect ratio grooves for comparing the performance of the two types of AFM tips. AFM scans (right) using the commercial and the CNT-enhanced AFM tip.
The CNT-enhanced AFM probe was used to scan highaspect ratio features. A test sample was fabricated in silicon in which 2.5 lm deep and 570 nm wide grooves were etched. Fig. 5 compares AFM scans using a commercial pyramidal AFM probe and the CNT-enhanced AFM probe. It is clear that the modified AFM probe has resolved the width significantly better than the standard pyramid shaped AFM tips without the CNT extension, and provided a better if not perfect profile of the deep trenches. A more thorough description of this experiment can be found in [9]. 4. Conclusion We have presented a monolithic electrothermal microgripper, and demonstrated pick-and-place of an as-grown
References [1] C.J. Kim, A.P. Pisano, R.S. Muller, M.G. Lim, Sensors and Actuators A—Physical 33 (1992) 221–227. [2] P. Kim, C.M. Lieber, Science 286 (1999) 2148–2150. [3] P. Boggild, T.M. Hansen, C. Tanasa, F. Grey, Nanotechnology 12 (2001) 331–335. [4] K. Molhave, T.M. Hansen, D.N. Madsen, P. Boggild, Journal of Nanoscience and Nanotechnology 4 (2004) 279–282. [5] K. Mølhave, T. Wich, A. Kortschack, P. Bøggild, Journal of Nanotechnology 17 (2006) 2434–2441. [6] S. Fatikow, S. Kray, V. Eichhorn, S. Tautz, in: Development of a Nanohandling Robot Station for Nanocharacterization by an AFM Probe, IEEE Mediterranean Conference on Control and Automation (MED), Ancona, Italy, June 28–30, 2006, WEA4-4. [7] K. Molhave, O. Hansen, Journal of Micromechanics and Microengineering 15 (2005) 165–1270. [8] D.N. Madsen, K. Molhave, R. Mateiu, P. Boggild, A.M. Rasmussen, C.C. Appel, M. Brorson, C.J.H. Jacobsen, Journal of Nanotechnology 1 (2003) 335–338. [9] K. Carlson, K.N. Andersen, V. Eichhorn, D.H. Petersen, k. Mølhave, I.Y.Y. Bu, K.B.K. Teo, W.I. Milne, S. Fatikow, P. Bøggild, Journal of Nanotechnology 18 (2007) 345501–345508. [10] H. Liu, K. Chao, J. Han, M. Meyyappan, Nano Letters 4 (2004) 1301–1308.