Examining epitaxial graphene surface conductivity and quantum Hall device stability with Parylene passivation

Abstract

Homogeneous, single-crystal, monolayer epitaxial graphene (EG) is the one of most promising candidates for the advancement of quantized Hall resistance (QHR) standards. A remaining challenge for the electrical characterization of EG-based quantum Hall devices as a useful tool for metrology is that they are electrically unstable when exposed to air due to the adsorption of and interaction with atmospheric molecular dopants. The resulting changes in the charge carrier density become apparent by variations in the surface conductivity, the charge carrier mobility, and may result in a transition from n-type to p-type conductivity. This work evaluates the use of Parylene C and Parylene N as passivation layers for EG. Electronic transport of EG quantum Hall devices and non-contact microwave perturbation measurements of millimeter-sized areas of EG are both performed on bare and Parylene coated samples to test the efficacy of the passivation layers. The reported results, showing a significant improvement in passivation due to Parylene deposition, suggest a method for the mass production of millimeter-scale graphene devices with stable electrical properties.

Atypical quantized resistances in millimeter-scale epitaxial graphene p-n junctions

“…20 EG pnJs can be utilized to circumvent most of the technical difficulties resulting from the use of metallic contacts and multiple device interconnections. Research in developing materials for gating and preserving properties of large devices has seen limited success with amorphous boron nitride, [21][22] atomicallylayered high-k dielectrics, [23][24][25][26] Parylene, [27][28][29] and hexagonal boron nitride, [30][31] whereas other materials have been more successful, such as (poly)-methyl methacrylate ((P)MMA), ZEP520A photoresist, tetrafluoro-tetracyanoquinodimethane (F4TCNQ), and chromium tricarbonyl. 16,[32][33] For millimeter-scale constructions, one major issue was fabricating correspondingly large pnJs.…”

The quantum Hall effect in the era of the new SI

“…The preceeding years were primarily dedicated to optimizing the technology and fabrication processes such that EG-based QHR devices could be deployed into US and global industries. A summary of this optimization process is illustrated in Figure 3 and represents years of efforts directed by multiple institutes [82][83][84][85][86][87][88][89][90]. In short, EG-based devices, to be deployable for metrological implementation and general global usage, required the quality of the graphene to be of high order, the device scalability to be of appreciable range (from micrometers to centimeters), the stability of electrical properties to be simple to achieve, and for more complex structures' fabrication and testing to be demonstrated (i.e.…”

Quantum Hall device data monitoring following encapsulating polymer deposition

“…After the growth and verification procedures described in the methods section, epitaxial graphene (EG) are fabricated into quantum Hall devices and characterized with a Janis Research cryostat and magnet system (model 8TM-TLSL-HE3–17). ∂ Four relevant quantum Hall parameters are the Hall resistance ( R xy ), electron density ( n e ) , mobility ( μ ) , and longitudinal resistivity ( ρ xx ), and they are all measured and calculated ( and , where W and L are the width and length of the Hall device, respectively) as a function of up to nine process steps described in detail in Reference [1] . An example of how these parameters are monitored is shown in Fig.…”

“…In one iteration of calibrating the Parylene deposition process, a 10.7 μm thickness was measured for one of the devices, which was tested to compare with the 720 nm thickness data presented in Ref. [1] , [1] based on identical process steps. ( Fig.…”

“…This section provides additional data for other devices that have been tested and exposed to the same environmental conditions as described in Ref. [1] , [1] . Fig.…”