M150 MEMS Analyzer for Ultra High Frequency Cantilever Measurement

By AZoSensors.com Staff Writers

Topics Covered

Introduction
Instrument Basic Principles
High Frequency Cantilever
AFM Cantilever Tuning
AFM Cantilever Measured by the M150 MEMS Analyzer
Results
Conclusion
About Ardic Instruments

Introduction

The atomic force microscope has brought a range of applications to academia and to industry marking the beginning of the nanotechnology era.

Due to advancements in AFM technology, the scan speed has recently been highly improved. The discovery of high frequency cantilevers played an important role in not only higher speed AFMs, but also higher resolution imaging.

The popular AC mode or semi-contact mode heavily depends on the precise tuning of the AFM to the cantilever resonance frequency. Unfortunately, inconsistent resonance frequencies can result from used cantilevers or cantilevers with manufacturing defects. Therefore it is both important to the user and to the manufacturer to properly measure the resonance frequencies.

Instrument Basic Principles

The M150 is a MEMS Analyzer used for characterizing microstructural mechanical properties. Using a simple point-and-shoot laser optical system, the user can quickly obtain resonance peaks of a microstructure through wide bandwidth frequency scanning and real-time Fourier transform (FFT).

By using non-contact optical measurement, the M150 is a highly effective technique for measuring resonance frequencies without altering the sample properties.

High Frequency Cantilever

High frequency cantilevers are primarily used for high speed scans. The cantilever is designed to have a high resonance frequency and low spring constant in order to increase its resolution and scan rate. Consequently, the appearance of the cantilever is thinner and smaller compared to traditional cantilevers. Mathematically, the equation of fc (Resonance frequency) and kc (Spring constant) is:

d is the cantilever depth, w is the width, L is the length, E is the Young's module and ρ is the material‘s density.

Silicon nitride (Si3N4), commonly used as the material for cantilevers, has the following Young’s modulus and material density:

Based on the mathematical description, it can meet the characteristics (such as high fc and low kc) of a high frequency cantilever design, the size dimensions of the cantilever design should be smaller for better result.

Also, according to the formula of Thermal noise, √((k_B * T) / kc ), where with the Boltzmann`s constant k_B, and temperature in Kelvin T, it is also found that high frequency tip cantilevers have as lower noise density which can reduce thermal noise.

AFM Cantilever Tuning

Surface characteristics are measured by AFMs by detecting forces between the cantilever tip and sample surface. The cantilever must have a specific elasticity and operate within its resonance frequency range during the experiment.

When a high quality AFM cantilever is being operated using the resonance frequency range provided by the original manufacturer, the resonance frequency will be a single peak in most ideal situations.

However, while a low quality cantilever is operated, it may be difficult to determine the resonance frequency due to excess noise. The M150 can be used to characterize the quality of AFM cantilevers by observing their FFT peaks, allowing users to verify cantilever resonance frequencies and manufacturers to confirm the manufacturing quality of their probes.

AFM Cantilever Measured by the M150 MEMS Analyzer

The aim is to use the M150 MEMS Analyzer to confirm if the resonance frequency of a high frequency cantilever is within the range provided by the manufacturer.

Sample: The sample depth is 0.7µm, length is 35µm and width is 42µm for a NanoWorld Arrow-UHF-SPL cantilever. The resonance frequency range is 0.7 ~ 2.0MHz.

Figure 1. Arrow-UHF-SPL SEM image

Process: Load the Arrow-UHF-SPL probe into M150 MEMS Analyzer, and measure 3 points along the length of the cantilever. Run each scan with 60s per point, and set resonant peaks between 1Hz and 4.2MHz during real-time Fourier transform.

Results

Table 1. Results of Arrow UHF-SPL measurement by M150 Analyzer

Location 1st spot 2nd spot 3rd spot
Tune frequency 1538544Hz 1538544Hz 1538544Hz

Figures 2, 3 and 4 show the 1st, 2nd and 3rd spot images.

Figure 2. First spot

Figure 3. Second spot

Figure 4. Third spot

Conclusion

Arrow-UHF-SPL are ultra-high frequency probes that have smaller dimensions when compared to conventional cantilevers. They can resonate at a very high frequency. The resonance frequency range given by the manufacturer is 0.7 ~ 2.0MHz. Table 1 shows the resonant frequency of Arrow-UHF-SPL measured by M150 MEMS ANALYZER. The resonant frequency of cantilever is 1.538MHz and this probe is operable in the frequency range given by the manufacture.

In Arrow-UHF-SPL probe experiments, spots were scanned from left to right along the length of the cantilever, the peak wave measured from high to low, and the detected resonance frequency was the first vibration mode of this probe. With the M150 MEMS ANALYZER it was possible to offer an accurate measurement of a high frequency probe, which will become increasingly more prevalent and critical in advanced AFM applications.

About Ardic Instruments

Ardic Instruments is an analytical equipment manufacturer aiming to serve the global scientific community with the best customer experience possible. Through a transparent, accessible, and community-driven approach, Ardic Instruments fosters a direct channel of communication between the end-user and the manufacturer.

Ardic Instruments produces atomic force microscopes, MEMS analyzers, and label-free molecular diagnostic platforms for both academic and industrial applications.

This information has been sourced, reviewed and adapted from materials provided by Ardic Instruments.

For more information on this source, please visit Ardic Instruments.

Date Added: Nov 27, 2013 | Updated: Nov 27, 2013
Ask A Question

Do you have a question you'd like to ask regarding this article?

Leave your feedback
Submit