Schematic of two finite-area planar surfaces to be made parallel to each other. Control of the relative alignment along the x, y, z directions, and the relative angular alignment θ x , θ y , θ z , is required to accomplish the desired parallelization. The Cartesian coordinate system is attached to the laboratory reference frame.
Schematic design of the nanopositioner with the major parts labeled: (a) the top subassembly is used to control the relative angular alignments θ x , θ y as well as to enable control of the relative alignment of the two planes along the x, y directions, (b) the bottom subassembly controls the relative alignment of the bottom plane along the x, y directions as well as the angular rotations about x, y, and z directions. The spatial separation is controlled using a z-linear stage and a piezoelectric actuator to control the position in z direction. (c) Sectional view of the top and bottom subassemblies assembled together by four columns (two of the columns are not shown for visual clarity).
Angular control of the top plane with the custom-built goniometer: (a) isometric view showing how rotation about y axis is controlled; (b) side view showing the preloaded spring and one of the sphere joints; (c) schematic view of the middle and inner frames and the extended top plane (shaded blue), with arrows showing equivalently where the motors push for the x (green) and y (yellow) axes; (d) schematic drawing demonstrating how the location of eucentric point remains unchanged during rotation of the two frames and hence the importance of placing the top plane as close to it as possible. The arm lengths where each stepper applies its equivalent force are also shown.
Control of the position of the top carrier in x and y directions. Three micrometer screws are used for this purpose: one for x direction and the other two for y direction adjustments. Upon reaching the final desired position of the top carrier, the location of the positioner is fixed by holding it rigidly against the inner frame using four screws as shown.
Schematic of the micro-devices: (a) top device representing the top planar surface; (b) bottom mesa device representing the bottom planar surface (shown upside-down); (c) schematic drawing showing the current amplifiers connected to the top electrodes and a voltage bias applied to the bottom electrode.
Dark field optical microscope (DFOM) and scanning electron microscope (SEM) images of the micro-devices: (a) SEM and (b) DFOM images of the top micro-device (with four gold contact pads); (c) and (d) SEM and DFOM images of the bottom mesa device, respectively.
Schematic of the fabrication procedure used to create the mesa micro-device. The ribs at the corners of the square mask ensure that the final top surface of the mesa structure resembles a square.
Characterization of planarity, surface roughness, and particle contamination. (a) AFM images of the top of a smooth and clean mesa surface and (b) line profiles of the mesa surface. These data show that the mesa surface has no appreciable deviations from planarity and a very small surface roughness (<1 nm rms). Similar results were obtained for the top surface (not shown). (c) An AFM image of a mesa surface with particulate contamination and the corresponding (d) DFOM image. A comparison of the AFM and DFOM images shows that particles as small as 10 nm in size can be readily detected using DFOM with our microscope system (20 ms exposure with the CCD camera) and the described device surfaces.
Description of the scheme used to parallelize the top and bottom surfaces. The optical alignment scheme ensures that corresponding points on the top chip plane and the bottom chip plane are at almost identical distances from each other (d ± 2 μm). The microfabricated devices are not drawn to scale.
Schematic drawing of the experimental process to quantify the parallelism achieved with depth-of-field based optical alignment. In this procedure, the electrodes integrated into the top device and bottom devices are used to identify when a contact (indicated by green color) is made.
Parallelization using integrated electrodes. (a) A representative trace displaying the sequence of contact formation between the electrodes of the top and bottom device for an approach speed of 2 nm/s. Here, a low signal level indicates an open contact, whereas a high level is a sign of contact. After the first contact is made, the remaining three electrodes contact the bottom device within a displacement of <4 nm. The displacement range over which the contacts are made is independent of the approach speed (0.2–10 nm/s, N = 8) and is consistently smaller than 5 nm. However, the sequence in which the pads make contact may differ between experiments. (b) A dark-field optical microscope (DFOM) image of the top and bottom devices that are spatially separated by a few micrometers (after optical alignment). (c) A DFOM image when all four top device's electrodes make electrical contact with the electrode of the bottom device.
Schematic describing the analysis of parallelization.
Estimates of the achievable spatial deviation from parallelism for ideal planar surfaces of different areas, using the custom-built nanopositioner.
The angular rotations about the x and y axes to obtain four simultaneous contacts between the top electrodes and the bottom electrode. The measured spatial deviation from parallelism, in eight independent measurements, right after optical alignment is also provided.
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