Accurate graphene quantum Hall arrays for the new International System of Units

Abstract

Graphene quantum Hall effect (QHE) resistance standards have the potential to provide superior realizations of three key units in the new International System of Units (SI): the ohm, the ampere, and the kilogram (Kibble Balance). However, these prospects require different resistance values than practically achievable in single graphene devices (~12.9 kΩ), and they need bias currents two orders of magnitude higher than typical breakdown currents IC ~ 100 μA. Here we present experiments on quantization accuracy of a 236-element quantum Hall array (QHA), demonstrating RK/236 ≈ 109 Ω with 0.2 part-per-billion (nΩ/Ω) accuracy with IC ≥ 5 mA (~1 nΩ/Ω accuracy for IC = 8.5 mA), using epitaxial graphene on silicon carbide (epigraphene). The array accuracy, comparable to the most precise universality tests of QHE, together with the scalability and reliability of this approach, pave the road for wider use of graphene in the new SI and beyond.

Long-term stability of molecular doped epigraphene quantum Hall standards: single elements and large arrays (R K/236 ≈ 109 Ω)

“…From this data the weighted mean is calculated, which is −4.4674 µΩ Ω −1 with standard deviation of weighted mean of 0.0041 µΩ Ω −1 . The exact calculations are described in related works [14]. Figure 3(b) shows the corresponding Allan deviation analysis [20] (using overlapping Allan deviation as in [14]).…”

“…The exact calculations are described in related works [14]. Figure 3(b) shows the corresponding Allan deviation analysis [20] (using overlapping Allan deviation as in [14]). The blue line is a fit to 1/t 1/2 , where t is elapsed measurement time.…”

“…This is problematic because carrier density control of graphene is crucial to tune the operating conditions for quantum resistance metrology [2,9]. We demonstrated a technique which yields potent and uniform doping of epigraphene by using molecular dopants and polymer encapsulation [11,13,14], and it allows an epigraphene QHR device to be tuned to operate at some desired temperature T, magnetic flux density B, and with critical current I C . It has previously been demonstrated that the molecular dopant technique yields longterm stable doping if the samples are kept in inert nitrogen atmosphere, with a relative change in carrier density around 0.02% per day [11].…”

Scalable Fabrication of Edge Contacts to 2D Materials: Implications for Quantum Resistance Metrology and 2D Electronics

“…Inspired by the method of forming edge contacts to graphene/hBN heterostructures, here we report a microfabrication strategy for the scalable microfabrication of electrical contacts to 2D materials based on the tri-layer resist system, which does not require encapsulation of the 2D material by hBN. Recently, we have used this method to produce nearly 3000 contacts to graphene and demonstrated the largest, most accurate array of graphene quantum resistors, using epitaxial graphene on silicon carbide (epigraphene) . This demanding application requires 100 % yield, i.e., the total contribution of all contact resistances has to be well below 100 nanoOhms.…”

“…By using the tri-layer resist method, compared to, e.g., single layer method, 24 we have observed a remarkably high yield in the fabrication of contacts and reproducibility in achieving consistently low contact resistance demonstrated in this and in our earlier work. 22 This is because the resist profile provides a clean liftoff when the metal deposition is performed by thermal evaporation and also by sputtering, thus giving additional flexibility when designing a microfabrication process.…”