Low-capacitance nanopore sensors on insulating substrates

A method of fabricating a nanopore sensor, the method comprising:

• depositing a first oxide layer on a first side of a sapphire substrate and a second oxide layer on a second side of the sapphire substrate opposite the first side;
• patterning the second oxide layer to form an etch mask having a mask opening in the second oxide layer;
• performing a crystalline orientation dependent wet anisotropic etch on the second side of the sapphire substrate using the etch mask to form a cavity having sloped side walls through the sapphire substrate to yield an exposed portion of the first oxide layer, each of the sloped side walls being a crystalline facet aligned with a respective crystalline plane of the sapphire substrate;
• depositing a silicon nitride layer on the first oxide layer;
• removing the exposed portion of the first oxide layer in the cavity, thereby defining a silicon nitride membrane in the cavity;
• and
• forming an opening through the silicon nitride membrane, wherein the opening is a nanopore with a diameter in a range of 1 nm to 20 nm,
• wherein the mask opening is in the shape of a hexagon, and
• wherein an edge of the hexagon is aligned at an offset angle α from a crystalline plane of the sapphire substrate, where 5°<α<55°.

A method of fabricating a nanopore sensor, the method comprising:

• depositing a first oxide layer on a first side of a sapphire substrate and a second oxide layer on a second side of the sapphire substrate opposite the first side;
• patterning the second oxide layer to form an etch mask having a mask opening in the second oxide layer;
• performing a crystalline orientation dependent wet anisotropic etch on the second side of the sapphire substrate using the etch mask to form a cavity having sloped side walls through the sapphire substrate to yield an exposed portion of the first oxide layer, each of the sloped side walls being a crystalline facet aligned with a respective crystalline plane of the sapphire substrate;
• depositing a silicon nitride layer on the first oxide layer;
• removing the exposed portion of the first oxide layer in the cavity, thereby defining a silicon nitride membrane in the cavity;
• and
• forming an opening through the silicon nitride membrane, wherein the opening is a nanopore with a diameter in a range of 1 nm to 20 nm,
• wherein the mask opening is in the shape of an equilateral triangle, and an edge of the equilateral triangle is aligned at an offset angle α from a crystalline plane of the sapphire substrate, and
• wherein the silicon nitride membrane is in the shape of an equilateral triangle for 0°<α<20° or 40°<α<60°.