Terms and Technology Glossary

Accuracy

Accuracy refers to the closeness of the actual achieved position to the intended target position. In most of the cases, accuracy is indicated as the mean result to the target value.

Sensitivity

In the field of nanopositioning, sensitivity refers to the ability of a system to detect and effectively react to even the slightest changes in position or displacement. Enhanced sensitivity empowers finer control and improved resolution in nanopositioning applications, thereby elevating precision and accuracy.

arQtika cryogenic nanopositioner employs capacitive sensors, which rely on variations in the active area as the stage moves. This advanced technology enables exceptional position sensitivity, reaching as low as 10 nm. Additionally, this approach minimizes heat dissipation as the capacitor operates with almost zero current flow.

Position Encoder

A position encoder is a sensor that accurately measures and provides feedback on the position or displacement of a nanopositioning stage. It plays a critical role in determining the stage's position and supplying feedback signals for closed-loop operation. By detecting position-related features on the scale, electrical signals can be generated which represents the position or displacement. Various encoding methods, including optical, resistive, magnetic, and capacitive approaches, can be used to measure position displacement or absolute position of the stage.

arQtika nanopositioning units are optimized for ultra-low temperatures, in every aspect, including the position encoder. The postion encoding technique is chosen to minimize heat dissipation. To achieve this, arQtika nanopositioners utilize a capacitive position encoder, which operates on a principle that results in ultra-low heat dissipation. The encoder operates with nearly zero current flow, allowing heat dissipation to be kept below 1uW, ensuring optimal performance in low-temperature environments.

Open Loop Operation

Open-loop operation is the control scheme where the position of the stage is not controlled with feedback from a position sensor. The position command is applied to the nanopositioner, and it moves accordingly based on previous calibration of the movement. The system does not have direct information about the actual position of the moving stage.

Stability

Stability is the system’s ability to maintain its desired static position over a long time frame without drift or movement, minimizing any undesired positional changes. The final stability of the system depends on many factors such as mechanical vibrations or thermal fluctuations.

Noise

Noise refers to undesired and random variations or disruptions in a system, which can arise from electrical and/or mechanical sources. In the context of nanopositioning, electrical noise and mechanical noise can both impact the system's performance.

In the case of piezoceramic actuators, their expansion or contraction is influenced by the electric field applied to them. As a result, electrical noise directly affects the position in a manner similar to mechanical noise.

Mechanical noise refers to disturbances caused by mechanical imperfections or vibrations within the nanopositioning system itself. It can arise from factors such as friction, system resonance, or instability in the mechanical components.

arQtika addresses these noise concerns through two key approaches. Firstly, it features a rigid structure that effectively reduces mechanical noise when the stage is at rest. This design minimizes disturbances originating from mechanical sources.

Secondly, the control electronics of arQtika are designed and developed to minimize electrical noise within the system. This ensures that unwanted fluctuations in the electric signals are kept to a minimum, reducing the impact of electrical noise on the system's performance.

By incorporating a rigid structure to mitigate mechanical noise and implementing robust control electronics to minimize electrical noise, arQtika enhances the precision and stability of the nanopositioning system.

Fighting vibrations at low temperatures originated from Dilution Refrigerators comes with the challenges of realizing a well-thermalized connection that at the same time is mechanically decoupling as much as possible. Onnes Technologies proudly offers cryogenic vibration isolation system (cVIS) to reduce the mechanical vibrations down to 10 pm/√Hz. The cVIS is a two stage mechanical low pass filter for the reduction of vibration level noise in cryostats.

Reliability

Reliability is the ability of the system to consistently perform its intended functions over an extended period, even under diverse conditions, without experiencing failure or significant performance degradation.

Cryo-walking technology, employed by Onnes Technologies' cryogenic nanopositioners, distinguishes itself from other positioning techniques by not relying on static and dynamic friction differences. This characteristic positions Onnes Technologies' cryogenic nanopositioners as the most reliable systems available.

Piezoelectric Material

Piezoelectric materials are a class of materials that have the ability to generate an electric charge in response to mechanical deformation, and conversely, to undergo mechanical deformation when subjected to an electric field. These materials have unique crystal structures or molecular arrangements that allow them to be utilized for ultra fine positioning by using a regulated external electric field.

Stick-Slip Motion

Stick-slip motion (a.k.a. slip-stick motion), a widely employed technique in nanopositioning applications, utilizes the contrast between static and dynamic friction forces within the system. It involves a linear actuator comprising a piezoceramic material coupled to the stage with a preload. During operation, as the linear actuator slowly expands, the static friction propels the stage in the expansion direction. Subsequently, the linear actuator rapidly contracts, enabling a period of sliding motion facilitated by dynamic friction. This cycle repeats, generating a sequence of intermittent steps to achieve the desired positioning.

The slip-stick motion is visualized in the figure below:

Walking-Piezo Motion

Historically, walking piezo actuator was introduced more than 10 years ago targeting the semiconductor industry that places significant importance on factors such as reliability, long term stability, and high position resolution.

Walking-piezo motion is a technique used in nanopositioning to achieve precise and controlled linear or rotational motion. It involves a series of piezoelectric actuator legs that sequentially move to generate continuous movement with high precision. In walking-piezo motion, the piezoelectric actuators are typically arranged in a configuration similar to legs. Each actuator consists of a piezoelectric stack bonded to a linear stage. The walking motion is achieved through a three step sequence: grip, shift, and release.

Onnes Technologies named this motion as Cryo-Walking, since Onnes Technologies is the only nanopositioner manufacturer that could implement the walking piezo technology for ultra low temperatures. In arQtika, there are four actuator legs used for nanopositioning. Initially, all the legs are in grip position to create preload. This establishes a firm grip between the actuators and the surface, preventing the stage from undesired moving.

The walking motion is visualized in the figure below: