Fast spiral-scan atomic force microscopy

In this paper, we describe a new scanning technique for fast atomic force microscopy. In this method, the sample is scanned in a spiral pattern instead of the well established raster pattern. A spiral scan can be produced by applying single frequency cosine and sine signals with slowly varying amplitudes to the x -axis and y -axis of an atomic force microscope (AFM) scanner respectively. The use of the single tone input signals allows the scanner to move at high speeds without exciting the mechanical resonance of the device and with relatively small control efforts. Experimental results obtained by implementing this technique on a commercial AFM indicate that high-quality images can be generated at scan frequencies well beyond the raster scans

Optimal integral force feedback and structured PI tracking control : application for objective lens positioner

Peer reviewedPostprin

Robust control of pendulum-type micro-vibration isolation system

A novel pendulum type of vibration isolation module is proposed in this paper which consists of passive and active layers. The active layer is consisted of a hollow ring-type piezoelectric actuator embedded in the vibration module, and an accelerometer is located on the payload disc to perform closed loop control. The passive layer is formed by an elastomer pad inserted between the active layer and payload disc for high frequency isolation. The equations of motion in the vertical and horizontal directions are derived using the Lagrangian approach. The transmissibility function is measured and used for setting performance specifications. The uncertainties due to the payload variations are included in generating the plant template. Then the controller based on the quantitative feedback theory is designed to achieve robustness as the payload of the plant varies from 40 to 60 Kg. Experiments are conducted to validate the performances the isolation module for both vertical and horizontal directions. The pendulum structure could reduce the first natural frequency in the horizontal direction to be about 1.875 Hz such that high frequency disturbance rejection can be achieved. Experimental results also demonstrate that the active control could reduce vibrations by more than 10 dB within the frequency range from 20-35 Hz and 20 dB at the first resonance. The time domain signals measured from the ground and payload with control on and off verify the performances of the vibration isolation system

A new scanning method for fast atomic force microscopy

In recent years, the atomic force microscope (AFM) has become an important tool in nanotechnology research. It was first conceived to generate 3-D images of conducting as well as nonconducting surfaces with a high degree of accuracy. Presently, it is also being used in applications that involve manipulation of material surfaces at a nanoscale. In this paper, we describe a new scanning method for fast atomic force microscopy. In this technique, the sample is scanned in a spiral pattern instead of the well-established raster pattern. A constant angular velocity spiral scan can be produced by applying single frequency cosine and sine signals with slowly varying amplitudes to the x-axis and y -axis of AFM nanopositioner, respectively. The use of single-frequency input signals allows the scanner to move at high speeds without exciting the mechanical resonance of the device. Alternatively, the frequency of the sinusoidal set points can be varied to maintain a constant linear velocity (CLV) while a spiral trajectory is being traced. Thus, producing a CLV spiral. These scan methods can be incorporated into most modern AFMs with minimal effort since they can be implemented in software using the existing hardware. Experimental results obtained by implementing the method on a commercial AFM indicate that high-quality images can be generated at scan frequencies well beyond the raster scans

Dynamics and Controls of Fluidic Pressure-Fed Mechanism (FPFM) of Nanopositioning System

Flexure or compliant mechanisms are employed in many precisions engineered devices due to their compactness, linearity, resolution, etc. Yet, critical issues remain in motion errors, thermal instability, limited bandwidth, and vibration of dynamic systems. Those issues cannot be negligible to maintain high precision and accuracy for precision engineering applications. In this thesis, a novel fluidic pressure-fed mechanism (FPFM) is proposed and investigated. The proposed method is designing internal fluidic channels inside the spring structure of the flexure mechanism using the additive manufacturing (AM) process to overcome addressed challenges. By applying pneumatic/hydraulic pressure and filling media into fluidic channels, dynamic characteristics of each spring structure of the flexure mechanism can be altered or adjusted to correct motion errors, increase operating speed, and suppress vibration. Additionally, FPFM can enhance thermal stability by flowing fluids without affecting the motion quality of the dynamic system. Lastly, the motion of the nanopositioning system driven by FPFM can provide sub-nanometer resolution motion, and this enables the nanopositioning system to have two linear motion in a monolithic structure. The main objective of this thesis is to propose and validate the feasibility of FPFM that can ultimately be used for a monolithic FPFM dual-mode stage for providing high positioning performance without motion errors while reducing vibration and increasing thermal stability and bandwidth

Sensorless vibration suppression and scan compensation for piezoelectric tube nanopositioners

Piezoelectric tube scanners are employed in high-resolution positioning applications such as scanning probe microscopy and nanofabrication. Much research has proceeded with the aim of reducing hysteresis and vibration-the two foremost problems associated with piezoelectric tube scanners. In this paper, two simple techniques are proposed for simultaneously reducing hysteresis and vibration: 1) A new dc accurate charge amplifier is shown to significantly reduce hysteresis while avoiding characteristic voltage drift. 2) Piezoelectric shunt damping, a technique previously resident in the field of smart structures, has been applied to damp tube vibration. By attaching an LCR impedance to a single tube electrode, the first mechanical mode is reduced in magnitude by more than 20 dB

Design and control of a self-sensing piezoelectric reticle assist device

Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Mechanical Engineering, 2013.This electronic version was submitted by the student author. The certified thesis is available in the Institute Archives and Special Collections.Cataloged from student-submitted PDF version of thesis.Includes bibliographical references (p. 233-239).This thesis presents the design and control techniques of a device for managing the inertial loads on photoreticle of lithography scanners. Reticle slip, resulting from large inertial loads, is a factor limiting the throughput and accuracy of the lithography scanners. Our reticle-assist device completely eliminates reticle slip by carrying 96% of the inertial loads. The primary contributions of this thesis include the design and implementation of a practical high-force density reticle assist device, the development of a novel charge-controlled power amplifier with DC hysteresis compensation, and the development of a sensorless control method. A lithography scanner exposes a wafer by sweeping a slit of light passing through a reticle. The scanner controls the motion of the reticle and the wafer. The reticle-stage moves the photoreticle. To avoid deforming the reticle, it is held using a vacuum clamp. Each line scan consists of acceleration at the ends of the line and a constant-speed motion in the middle of the line, where exposure occurs. If the reticle's inertial force approaches or exceeds the clamp's limit, nanometer-level pre-sliding slip or sliding slip will occur. The assist device carries the inertial load by exerting a feedforward force on the reticle's edge. The device retracts back during the sensitive exposure interval to avoid disturbing the reticle. The reticle is at the heart of the scanner, where disturbances directly affect the printing accuracy. Our reticle assist device consists of an approach mechanism and a piezoelectric stack actuator. The approach mechanism positions the actuator 1-m from the reticle edge. The actuator, with 15-[mu]m range, extends to push on the reticle. We have developed control techniques to enable high-precision high-bandwidth force compensation without using any sensors. We have also developed a novel charge-controlled amplifier with a more robust feedback circuit and a method for hysteresis compensation at DC. These technologies were key to achieving high-bandwidth high-precision sensorless force control. When tested with a trapezoidal force profile with 6400 N/s rate and 60 N peak force, the device canceled 96% of the inertial force.by Darya Amin-Shahidi.Ph.D

Realisierung der Steuerungs-/Regelungsalgorithmen mittels FPGA für ein hochauflösendes und schnelles Rasterkraftmikroskop mit aktivem Cantilever

Die Entwicklungen des Rasterkraftmikroskops (AFM: atomic force microscope) betrafen alle seine Komponenten, angefangen von Kraftsensoren, Regelungstechniken, Materialien, und Ausrüstung bis zu den Betriebsmoden. Die meisten dieser Entwicklungen haben das Ziel, die Auflösung des AFM zu verbessern und seine Geschwindigkeit zu erhöhen. Meine Doktorarbeit versucht, zur Entwicklung der Rasterkraftmikroskopie dadurch beizutragen, dass neue Steuerungs- und Regelungsmethoden für das AFM-System mit dem selbstaktuierten piezoresistiven Cantilever (Aktiver Cantilever) als Kraftsensor entworfen und auf Basis der "Field Programmable Gate Array" (FPGA) implementiert werden. In dieser Arbeit wird die Performanz des AFM-Systems mit aktivem Cantilever in der "Geschwindigkeit-Auflösung-Ebene" verbessert. Dafür werden digitale Regelungs- und Steuerungsalgorithmen mit hohem Durchsatz für das AFM-System entworfen und auf FPGA implementiert. Eine Methode wird im Rahmen dieser Arbeit für die automatische Annäherung der Sonde in Richtung der Oberfläche der Probe in einer sehr schnellen und sicheren Art und Weise entwickelt. Die schnelle Annäherung führt zu Verbesserung der AFM-Produktivität besonders bei den Anwendungen, die eine Wiederholung des Annäherungsprozesses während der gleichen Sitzung erfordern (step and image). Rückkoppelungsregelung und Vorwärtsregelung auf Basis eines FPGA werden untersucht, entworfen und implementiert, um die Auswirkungen der Hysterese und Vibrationen des Scanners (Positioniersystem) zu kompensieren. Es wird gezeigt, dass sich durch die Normierung der Hysterese-Kurven die Komplexität des Hysterese-Modells und dadurch des inversen Modells der Hysterese stark reduzieren lässt. Ein neues alternatives Verfahren zur Charakterisierung der Hysterese mittels des AFM-Amplitudenbilds wird erläutert. Der Scanner wird als lineares System höherer Ordnung betrachtet und identifiziert. Ein digitaler Kompensator wird zum Unterdrücken der Scanner-Vibration entwickelt und im FPGA implementiert. Die Scan-Trajektorie in den XY-Richtungen hat einen signifikanten Einfluss auf die Wahl der Steuerungsarchitektur und die erreichbare Scan-Geschwindigkeit. Dafür werden verschiedene Methoden ("Input-Shaper", sinusförmiges und spirales Scannen) in dieser Arbeit implementiert. Zusätzlich werden eine nichtlineare Erfassungsmethode des AFM-Bildes und eine Phasenkorrektur verwendet, um die Verzerrung des AFM-Bildes aufgrund der nicht-linearen Scansignale zu vermeiden. In dieser Arbeit wird eine neue Struktur des digitalen Lock-In entwickelt, der die Amplitude und Phase der Cantilever-Schwingung sehr schnell ermitteln kann. Die Detektionszeit ist kleiner als eine Schwingungsperiode. Die Regelung für ein "Z-Scanner-lose-AFM" wird entworfen und auf FPGA implementiert. In diesem System wird der TMA (Thermomechanischer Aktuator) des aktiven Cantilevers anstatt des Z-Piezoaktuator verwendet, um die Topographie der gescannten Oberfläche zu verfolgen. Dieses Prinzip wird ausgenutzt, um ein AFM-System mit einem aktiven Cantilever-Array (4 Cantilever) zum parallelen Scannen einer großen Oberfläche (0.5mm x 0.2mm) zu entwickeln. Als effektive Scan-Geschwindigkeit werden 5,6 mm/s erreicht. Im Rahmen dieser Arbeit wird eine neuartige adaptive Variante zur Erhöhung der Scangeschwindigkeit entwickelt. Diese Methode verhindert ebenfalls effektiv das Sättigungsproblem, das beim Scannen der Oberflächen-Topographien mit hohem Aspekt-Verhältnis entsteht. Verglichen mit einem Standard-Regler ermöglicht der adaptive Regler eine deutlich höhere Stufenauflösung bei vergleichbaren Scanraten. Daher wird das Scannen vier- bis sechsmal schneller bei gleicher Abbildungsqualität. Beim Scannen mit einer kleinen Kraft gibt es sogar eine bis zu 17-fache Verbesserung.The developments relating to the atomic force microscope (AFM) involved all its components, from the force sensors, control techniques, materials and equipment to its operating modes. The majority of these developments have the aim of improving the resolution of the AFM and enhancing its speed. My doctoral thesis endeavours to contribute to the development of atomic force microscopy by designing new control methods for the AFM system with the self-actuating piezoresistive cantilever (active cantilever) as a force sensor and implementing them based on the “Field Programmable Gate Array” (FPGA). In this thesis, the performance of the AFM system with active cantilever is improved in the “speed-resolution plane”. Digital open-loop and closed-loop control algorithms with high throughput are designed for the AFM system and implemented on the FPGA. During the course of this doctoral thesis, a method is designed for the automatic approach of the probe towards the surface of the sample in a very fast and safe manner. A rapid approach leads to improved AFM productivity particularly with applications that the approach process to be repeated within the same session (step and image). The thesis studies, develops and implements open-loop and closed-loop control based on an FPGA to compensate for the effects of the hysteresis and vibrations of the scanner (positioning system). It shows that normalisation of the hysteresis curves allows the complexity of the hysteresis model and thus the inverse model of the hysteresis to be significantly reduced. A new alternative method for characterization of the hysteresis by means of the AFM amplitude image is explained. The scanner is viewed and identified as a higher-order linear system. A digital compensator is developed to suppress scanner vibration and is implemented in the FPGA. The scan trajectory in the XY direction has a significant influence on the choice of the control architecture and the achievable scan speed. Various methods (“Input Shaper“, sinusoidal and spiral scanning) are implemented in this thesis to achieve this. In addition, a non-linear method for recording the AFM image and phase correction are used to avoid the distortion of the AFM image due to the non-linear scan signals. This thesis develops a new digital lock-In structure, which can very rapidly detect the amplitude and phase of the cantilever oscillation. The detection time is less than one oscillation period. The control for a “Z scanner-less AFM” are developed and implemented on the FPGA. This system uses the TMA (Thermomechanical Actuator) of the active cantilever instead of the Z-piezo actuator to track the topography of the scanned surface. This principle is used to develop an AFM system with an active cantilever array (4 cantilevers) for the parallel scanning of a large surface (0.5 mm x 0.2 mm). 5.6 mm/s are arrived at as the effective scanning speed. This thesis also develops an innovative adaptive version for increasing scanning speed. This method also effectively prevents the saturation problem, which occurs when scanning the surface topographies with a high aspect ratio. Compared to a standard controller, the adaptive controller allows a much higher step resolution of at comparable scan rates. Therefore, the scanning becomes four to six times faster with the same image quality. When scanning with a small force, there is even an up to 17-fold improvement