The bare cavity resonance is at 10.6 GHz. It will require measuring a plain substrate and the target 2D film on a single side of an identical substrate, e.g., quartz, SiC, PET, glass, Si. We can complete the measurement under ambient conditions and this will take approximately 2-3 minutes. The closed cavity technique can measure a large sheet resistance range: 50 Ω/sq to 1 MΩ/sq.
Uniform mono- or a few layer 2D films on a single side of a low-loss substrate.
Sample size in between 3×3 mm2 and 12×12 mm2
Substrate thickness in between 200 µm to 1000 µm
The ratio of the film’s area to the substrate area should be ideally one (full coverage), otherwise it must be accounted for in calculating the sheet resistance
Open (and scanning) cavity
The NPL automated wafer scanning system [5-7], measures the target 2D film on a single side of a substrate, e.g., quartz, SiC, PET, glass, Si, in comparason with a plain substrate of the same material. The dielectric resonator frequncy is at 3.5 GHz. We can complete the measurement under ambient conditions. Scan time is 100 ms per step. A typical wafer-scale test duration is 20 min. Spatial variation in the sheet resistance (through linewidth) and dielectric environment (through frequency shift) can be mapped. Spatial resolution depends on the opening: 5 to 20 mm. Flexible measurement scheme: the film-covered side of the substrate can face up or down. The system is capable of measuring a large sheet resistance range: 50 Ω/sq to 1 MΩ/sq.
The Microwave Resonator can offer a series of benefits to organisations invovled in producing or developing next generation advanced materials or products related to Graphene/2D materials, thin films (including. batteries, coatings (optical and protective), displays (ITO film) and electronics.
The issue of non-invasive electrical measurement is common to a wide range of manufacturers in digital electronics, communications and semiconductor fabrication sectors. The cost of rejected wafers or other mass produced batch samples can be significant. The ability to monitor in-line production with no need to remove samples for batch testing can bring enormous cost savings and improved quality of end product.
Measurement of the electrical properties of thin films is an increasingly demanding issue for fabrication of large scale electrical components, both active and passive. Quality control demands accurate measurement of e.g. sheet resistance over large wafer scale production. High speed, combined with non-invasive measurement, are critical.
The microwave resonator technique is applicable across a range of spatial resolutions, from millimetres to micrometres. An entire 200 mm diameter wafer can be scanned at 10mm resolution (500 measurements) in ~ 10 minutes for present prototype system.
- L. Hao, J. Gallop, S. Goniszewski, O. Shaforost, N. Klein, and R. Yakimova ‘Non-contact method for measurement of the microwave conductivity of graphene’, Applied Physics Letters, 103 123103 (2013)
- L. Hao, J. Gallop, Q. Liu and J. Chen, ‘ Microwave method for high frequency properties of graphene’, IET Circuits Devises Syst., 9, (6), 397-402 (2015)
- L Hao, C Mattevi, J Gallop, S Goniszewski, Y Xiao, L Cohen and N Klein, ‘Microwave surface impedance measurements on reduced graphene oxide’, Nanotechnology v.23 285706 (2012)
- Electrical characterisation of graphene using non-contact and high-throughput methods, GRACE Good Practice Guide, http://empir.npl.co.uk/grace/
- P. Bøggild et al. “Mapping the electrical properties of large-area graphene”, 2D Mater. 4, 042003 (2017)
- O. Shaforost et al. “Contact-free sheet resistance determination of large area graphene layers by an open dielectric loaded microwave cavity” Journal of Applied Physics 117, 024501 (2015)
- M. Naftaly et al. “Sheet Resistance Measurements of Conductive Thin Films: A Comparison of Techniques” Electronics 10, 960 (2021)
Read about our research into the characterisation of graphene and other 2D materials
A look at the work we are doing to developing quantum sensors for single quantum particle detection