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Quantitative Electrical Measurements


Figure 1 : Schematic diagram showing how the ResiScope works. A DC bias is applied between the sample and a conductive AFM tip. The tip is held at virtual ground, and sample resistance is measured through a fast-response amplifi er module (HPA), independent of the AFM imaging feedback signal. Unique to the ResiScope, the module will auto-calibrate when the system is started, using internal precision resistors as references to provide quantitative data.


current between the probe and the sample is limited as the module introduces a resistor in series to the sample resistor. T is has the result of minimizing the local eff ect of oxidation or electrochemistry, thereby protecting the conductive probe from possible high-current damage. ResiScope mode vs. conductive AFM . T ere are similar-


ities and diff erences between conductive AFM mode and ResiScope mode. Both techniques require a conducting AFM tip and use contact mode imaging to scan a sample. However, conductive AFM covers only a few orders of magnitude, can only measure current, and does not limit damage to the sample. Conductive AFM data cannot be acquired simultaneously with other imaging modes.


ResiScope can operate in oscillating mode, over 10 orders of magnitude of resistance, and limits the current to minimize damage to the sample. T e ResiScope measures resistance or current and can provide I/V spectroscopy data. Other imaging modes can be measured simultaneously or in the same location with ResiScope mode. Soſt ResiScope mode for compliant samples . For the soſt mode, the AFM probe only stays in contact with the sample during a short period of time. T is is done with a constant force control, which allows the ResiScope module to measure the resistance and the current in the best conditions for quanti- tative measurements. T e tip is then retracted and moved to the next point. Applied as an intermittent contact mode, there is no friction with this technique. Because the measurement is done at constant force, the measurements are quantitative.


Figure 2 : Standard ResiScope imaging versus Soft ResiScope imaging for an SRAM chip, indicating equivalent results for topography (left) and resistance (right). The displayed upper half of each image was measured in Soft ResiScope mode and is comparable to the displayed lower halves that were acquired with the standard ResiScope imaged using contact mode. The cross-section analysis shows similar results between the two techniques for the same sample, with the red line for Soft ResiScope and the blue line corresponding to the standard ResiScope data. Image width = 30 µm.


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To show there is no diff erence between the standard and Soſt ResiScope modes for non-compliant samples, images were acquired of a static random access memory (SRAM) chip sample. Figure 2 shows topography and resistance images acquired in each mode. For each image, the displayed upper half was acquired in the Soſt ResiScope mode with intermittent contact. T e lower half of each image was taken in the standard ResiScope mode with contact mode imaging. T e cross-sectional analysis below the images demonstrates nearly identical results between the standard and Soſt ResiScope modes. T e red line corresponds to a line scan from the Soſt ResiScope image. T e blue line


www.microscopy-today.com • 2015 November


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