Dynamic in-situ electrical and interferometry measurement capability with high resolution X-ray diffraction synchronisation

With the US electronics giant IBM having recently filed the first patents for piezoelectric transistors, European physicists, materials scientists and metrologists have joined forces in a project called Nanostrain to develop the metrology and the understanding necessary to drive innovation and enable the development of novel electronic devices based on the control of strain at the nano-scale [1].

As part of this collaborative project, the UK National Physical Laboratory and the XMaS beamline team have worked closely together to combine very different techniques into a unique capability now in operation at the XMaS beamline (Fig. 1). X-ray diffraction, which is used to measure crystallographic changes at the atomic level, and optical interferometry, to measure displacement, has been coupled at the XMaS beamline.

Fig. 1: Interferometer and newly designed sample holder fitted onto the XMaS Huber diffractometer.

This new facility has been incorporated with the recently developed [2] in-situ/in-operando capability to apply an AC electric field to the specimen of interest and, if ferroelectric, measure the electrical polarisation. This comprehensive system for strain characterisation in single crystals and thin films enables scientists to investigate different strain components as functions of external stimuli (electric field amplitude, frequency, phase, duration, waveform, etc) working at different lengths scales: from micrometre displacements (global strain) to hundreds of femtometers (atomic strain) as well as the possibility to explore different device geometries and electrode configurations.

The combined information (Fig. 2) allows new insights to be gleaned on the correlation between induced strain and material properties, information of crucial importance for the development of novel devices such as IBM’s patented Piezoelectric Effect Transistor. This new capability was commissioned at the XMaS beamline in March 2014, with the first experiments performed in July 2014. The success of the integration has been proven with the observation of interferometrically measured displacements down to 50 picometers, which, when combined with 10 Angstroms lattice displacements measured with X-rays, provides an unprecedented and comprehensive level of information [3].

Fig. 2: Simultaneous acquisition of the dynamic response of a ferroelectric material: electrical polarization (green), strain calculated from d-spacings (X-rays, blue) and displacement (interferometry, red).

Measurement challenges and alignment issues have been addressed by identifying the best measurement practices and incorporating them into the control software for a more user-friendly facility. After this initial success, the next step will be the development of a complex sample environment to allow for temperature, electric and magnetic field applications to be investigated, and last but not least, the system will be upgraded and pushed into the MHz frequency domain. This will be a crucial step in enabling the understanding of materials and devices near real operational conditions: AC control fields and >MHz frequencies.

References
[1] Nanostrain home page
[2] J. Wooldridge, S. Ryding, S. Brown, T. L. Burnett, M. G. Cain, R. Cernik, R. Hino, M. Stewart, and P. Thompson, “Simultaneous measurement of X-ray diffraction and ferroelectric polarization data as a function of applied electric field and frequency,” J Synchrotron Rad, vol. 19, no. 5, pp. 710–716, Jul. 2012.
[3] C. Vecchini, P. Thompson, M. Stewart, A. Muniz-Piniella, S. R. C. McMitchell, J. Wooldridge, S. Lepadatu, L. Bouchenoire, S. Brown, D. Wermeille, O. Bikondoa, C. A. Lucas, T. P. A. Hase, M. Lesourd, D. Dontsov, and M. G. Cain, “Simultaneous dynamic electrical and structural measurements of functional materials,” Rev. Sci. Instrum., vol. 86, no. 10, pp. 103901–10, Oct. 2015.