Prof Neil Alford runs the Physical Electronics and Thin Film Materials group in the Department of Materials, Imperial College. The group have internationally recognised expertise in Pulsed Laser Deposition of ferroelectric based thin films and multilayer structures and their application for microwave tuneable devices. Their interests and research activities span development of methods for deposition of BSTO thin films using single target and two target source development of methods for improving the microwave properties of ferroelectric thin films,development of methods for tailoring the temperature coefficient of capacitance in ferroelectric varactors; the use of X-ray Diffraction and Raman microscopy to investigate thin film, out- and in-plane structural perfection; development of methods for testing the microwave properties of ferroelectric based multilayers; development of multilayered structures and fabrication of novel microwave devices such as tunable dielectric resonators with ferroelectric and piezoelectrics and tuneable filters based on high Q-factor dielectric resonators.
Recent research publications:
1) A. Kozyrev, M. Gaidukov, A. Gagarin, A. Altynnikov, V. Osadchy, A. Tumarkin, P. K. Petrov, and N. M. Alford Evaluation of the space charge trap energy levels in the ferroelectric films , J APPL PHYS , 2009 , Vol: 106 , ISSN: 0021-8979
2) Axelsson AK , Valant M , Fenner L , Wills A, Alford N M Chemistry of post-annealing of epitaxial CoFe2O4 thin films , THIN SOLID FILMS , 2009 , Vol: 517 , Pages: 3742 - 3747 , ISSN: 0040-6090
3) Breeze JD , Perkins JM , McComb DW , N M Alford Do Grain Boundaries Affect Microwave Dielectric Loss in Oxides? , J AM CERAM SOC , 2009 , Vol: 92 , Pages: 671 - 674 , ISSN: 0002-7820
4) Breeze, J, Krupka, J, Centeno, A, Alford, NM, Temperature-stable and high Q-factor TiO2 Bragg reflector resonator, APPL PHYS LETT, 2009, Vol: 94, ISSN: 0003-6951
5) Breeze, J, Krupka, J, Alford, NM, Enhanced quality factors in aperiodic reflector resonators, APPL PHYS LETT, 2007, Vol: 91, ISSN: 0003-6951
Facilities within the research group:
We have several thin film deposition techniques available, including a Neocera pulsed laser ablation system (PLD), which can be used to manufacture a range of different oxide materials, including novel materials using targets made in-house. Prototype and proof-of-principle device manufacture is also possible with the new facilities at Imperial College for nanolithography. We have recently acquired a third chamber that can perform spread composition deposition, useful for combinatorial methods.
For measurement of microwave properties we have three Agilent parameter network analysers (PNA), which are used with microwave probe-stations and resonant cavities for characterising thin films and dielectrics at frequencies up to 40GHz. The microwave cavities have been designed which are tuneable, and which are used to perform measurements of loss (Q), permittivity and temperature coefficient of resonant frequency (TCf) down to cryogenic temperatures as low as 15 K. The equipment is also used to measure the surface resistance and the distribution of critical currents in high temperature superconductors. An impedance/gain-phase analyser with dielectric test fixtures is used for determining the low frequency properties of dielectrics, ferroelectrics, the Q of MRI receive coils and the impedance of piezoelectrics. We also have two probe stations providing on-wafer measurements of thin films and devices under external electrical bias and magnetic field (up to 0.15T) applied in horizontal and vertical directions, in a wide temperature (10K - 600K) and frequency (d.c. - 40 GHz) ranges. We have an Agilent RF-LCR meter capable of performing a range of measurements on ferroelectrics and semiconductors in the frequency range 1 Hz to 3GHz and an Agilent B1500 Semiconductor Analyser with high resolution module (HRSMU) that allows d.c. current measurements with 1 fA resolution.
We can perform a full range of P-E loop analysis over a range of temperatures using a ferroelectric tester on both thick film and bulk materials. A Radiant Technologies Precision LC unit is used to measure polarisation or current against voltage or electric field using voltages up to ±10KV with a high voltage power amplifier. Polarisation-Field loops obtained using the standard triangular wave or a user customised voltage profile show the ferroelectric behaviour of bulk samples while the memory effect and values of effective capacitance and dielectric constant can be measured using customised pulse measurements or the standard PUND (positive up, negative down) measurement. Using the thermal chamber attached to a liquid nitrogen cylinder ferroelectric measurements in the range of -184.4°C to 315.5°C can be obtained which can be used to find the Curie temperature and examine pyroelectric behaviour. In addition the unit can be used to measure current-voltage or capacitance-voltage characteristics, resistance measurements, leakage current and by subjecting the sample to a series of pulses, fatigue, imprint and loss of remnant polarisation.
We have recently commissioned a Teraview THz spectrometer for performing measurements to 4 THz.