EP-4737895-A2 - FABRICATION OF TUNNELING JUNCTIONS WITH NANOPORES FOR MOLECULAR RECOGNITION

EP4737895A2EP 4737895 A2EP4737895 A2EP 4737895A2EP-4737895-A2

Abstract

Embodiments of the present technology may allow for improved and more reliable tunneling junctions and methods of fabricating the tunneling junctions. Electrical shorting issues may be reduced by depositing electrodes without a sharp sidewall and comer but instead with a sloping or curved sidewall. Layers deposited on top of the electrode layer may then be able to adequately cover the underlying electrode layer and therefore reduce or prevent shorting. Additionally, two insulating materials may be used as the dielectric layer may reduce the possibility of incomplete coverage and the possibility of flaking. Furthermore, the electrodes may be tapered from the contact area to the junction area to provide a thin electrode where the hole is to be patterned, while the thicker contact area reduces sheet resistance. The electrode may also be patterned to be wider at the contact area and narrower at the junction area.

Inventors

TOPOLANCIK, JURAJ
MAJZIK, Zsolt
MITCHELL, Flint

Assignees

F. Hoffmann-La Roche AG
Roche Diagnostics GmbH

Dates

Publication Date: 20260506
Application Date: 20190409

Claims (15)

A method of manufacturing a system for analyzing a molecule, the method comprising: depositing a first conductive material on a surface of a substrate to form a first electrode ; forming an insulating layer on the first electrode; depositing a second conductive material on the insulating layer to form a second electrode ; and defining a nanopore aperture through the substrate, the first electrode, the insulating layer, and the second electrode; wherein each of the first electrode and second electrode respectively taper from a contact area where the electrodes do not overlap to a junction area where they do overlap.
The method of claim 1, wherein forming the insulating layer comprises: depositing a first insulating material to a first thickness on the first electrode, defining a first via in the first insulating material to expose a portion of a top surface of the first electrode, depositing a second insulating material to a second thickness on the first insulating material, the second thickness being less than the first thickness, depositing the second insulating material on the portion of the top surface of the first electrode to define a second via, and depositing the second conductive material on top of the second insulating material, wherein: defining the aperture comprises removing material defining a portion of a bottom surface of the second via, and the aperture is defined in the second insulating material and not the first insulating material.
The method of claim 2, wherein: depositing the first conductive material is by biased target deposition, and defining the first via comprises patterning using electron beam lithography and wet etching the first insulating material.
The method of claim 1, wherein the non-zero degree angle is from 85 to 95 degrees.
A system for analyzing a molecule, the system comprising a device, the device comprising: a first electrode comprising a first conductive material, the first electrode ; a second electrode comprising a second conductive material, the second electrode ; an insulating layer disposed between the first electrode and the second electrode; wherein: a nanopore aperture is through the first electrode, the second electrode, and the insulating layer; and wherein each of the first electrode and second electrode respectively taper from a contact area where the electrodes do not overlap to a junction area where they do overlap.
The system of claim 5, further comprising: a power supply in electrical communication with at least one of the first electrode or the second electrode, and an electrical meter in electrical communication with at least one of the first electrode or the second electrode.
The system of claim 6, wherein the power supply is a first power supply, the system further comprising: a second power supply configured to apply an electric field through the aperture, the second power supply is not in electrical communication with the first electrode and is not in electrical communication with the second electrode.
The system of claim 5, the aperture is cylindrical.
The system of claim 5, wherein: the insulating layer comprises a first insulating material and a second insulating material, a first portion of the second insulating material is disposed between the first insulating material and the second electrode, a second portion of the second insulating material is disposed between the first electrode and the second electrode, the first insulating material is characterized by a first thickness, the second insulating material is characterized by a second thickness, the first thickness is greater than the first thickness, and the aperture is defined in the second insulating material and not the first insulating material.
The system of claim 5, wherein: the first electrode is formed by: depositing the first conductive material at a non-perpendicular angle while rotating the substrate after forming a first resist layer having an overhang.
The system of claim 5, wherein: the first electrode is characterized by a thickness and a width, the first electrode has an end, the thickness of the first electrode tapers from the end to a portion of the first electrode defining a portion of the aperture, and the width of the first electrode tapers from the end to a portion of the first electrode defining the portion of the aperture.
The system of claim 11, wherein: the second electrode is characterized by a thickness and a width, the second electrode has an end, the thickness of the second electrode tapers from the end to a portion of the first electrode defining a portion of the aperture, and the width of the second electrode tapers from the end to a portion of the second electrode defining the portion of the aperture.
The system of claim 7, further comprising: a third electrode in electrical communication with the second power supply, a fourth electrode, wherein: the aperture is centered around a longitudinal axis, and the longitudinal axis intersects the third electrode and the fourth electrode.
The system of claim 5, wherein the aperture is characterized by a diameter in a range of 2 nm to 30 nm; and/or the insulating layer is characterized by a thickness in a range of 1 nm to 2 nm.
A method of analyzing a molecule, the method comprising: applying a voltage across a first electrode and a second electrode separated by an insulating layer, ; contacting the molecule to the first electrode and the second electrode across the insulating layer in a nanopore aperture; measuring an electrical characteristic through the first electrode and the second electrode; and identifying a portion of the molecule based on the electrical characteristic, wherein: the aperture is through the first electrode, the second electrode, and the insulating layer; wherein each of the first electrode and second electrode respectively taper from a contact area where the electrodes do not overlap to a junction area where they do overlap.

Description

CROSS-REFERENCE TO RELATED APPLICATIONS This application claims priority to U.S. Provisional Application No. 62/654,894, filed April 9, 2018, the contents of which are hereby incorporated by reference in its entirety for any and all purposes. FIELD This application relates to systems to analyze molecules using tunnel junctions, methods to make such systems, and methods to use such systems. Such analysis of molecules can include sequencing biological polymers, such as nucleic acids. BACKGROUND Nanopores have the ability to detect single molecules, which is promising technology in the field of chemical and biological detection. For example, nanopores may be used for nucleic acid sequencing. Solid-state nanopores are one type used for rapidly bio-sensing a molecule sensing technique. In some cases, solid-state nanopores form a channel in an ionic liquid between two electrodes. The two electrodes may not be part of the nanopore itself but may be positioned in the ionic liquid. As a molecule passes though the nanopore channel, the current and other electrical characteristics through the channel change. These electrical characteristics can provide information on the molecule, but fabrication issues may make identifying individual nucleotides in a nucleic acid molecule difficult. Nanopore devices use tunneling recognition. Tunneling recognition is based on placing a nucleotide of a nucleic acid between electrodes, which may be in the nanopore device itself. The orbitals of the nucleotide will allow electrons to transfer from one electrode to the other, creating a tunneling current. Dimensions and other properties of solid-state nanopores may be difficult to adapt to a mass production process. To sequence nucleic acid molecules with ionic current, nanopore dimensions may need to be on the order of nanometers, e.g., less than 2 nm. Creating a channel of this size may require precise and expensive techniques. However, reducing dimensions of the nanopore may result in incomplete or poor wetting needed for the nanopore to function as a sensing device. Improvements in the design and manufacturability of nanopore-containing devices used in chemical and biological detection and processes involving the devices are still needed. Design and manufacturability improvements should not come at the expense of accurate and precise analysis. These and other issues are addressed by the technology described in this document. BRIEF SUMMARY For tunneling junctions, a thin dielectric between two metal electrodes is desired. A tunneling junction may include a hole through the electrodes and the dielectric. Fabricating these tunneling junctions, with dimension on the order of nanometers, is difficult. Electrodes may be patterned perpendicular to each other for alignment purposes. However, the perpendicular alignment of electrodes may result in shorts resulting from the sharp sidewalls of the electrodes and the thin dielectrics covering the sharp sidewalls. Additionally, a thin dielectric may itself be a poor barrier for shorting. Metal from an electrode may become embedded in the dielectric. The metal along with dielectric material may flake off, creating a void and possibility for a short. Furthermore, electrode thickness may also present a challenge. Because a hole may be patterned in the electrode, a thin electrode may make patterning easier. However, a thin electrode also results in increased sheet resistance. Embodiments of the present technology may allow for improved and more reliable tunneling junctions and methods of fabricating the tunneling junctions. Electrical shorting issues may be reduced by depositing electrodes without a sharp sidewall and corner, but instead with a sloping or curved sidewall. Layers deposited on top of the electrode layer may then be able to adequately cover the underlying electrode layer and therefore reduce or prevent shorting. Additionally, two insulating materials may be used as the dielectric layer, thereby reducing the possibility of incomplete coverage and the possibility of flaking. Furthermore, the electrodes may be tapered from the contact area to the junction area to provide a thin electrode where the hole is to be patterned, while the thicker contact area reduces sheet resistance. The electrode may also be patterned to be wider at the contact area and narrower at the junction area. A better understanding of the nature and advantages of embodiments of the present invention may be gained with reference to the following detailed description and the accompanying drawings. BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1A shows a metal-insulator-metal junction according to embodiments of the present invention.FIGS. 1B and 1C show views of a solid-state nanopore device according to embodiments of the present invention.FIG. 1D illustrates areas of a solid-state nanopore device according to embodiments of the present invention.FIG. 2 shows a diagram of a system 200 with a device 201 without electrodes with v