Controlled dielectric breakdown

Controlled dielectric breakdown
Leakage current against time during breakdown, schematically
Classification	Nanopore fabrication
Inventor	Harold Kwok, Kyle Briggs and Vincent Tabard-Cossa (University of Ottawa)
Year	2014
Related	Focused ion beam; Tesla coil lighter pore fabrication

Controlled dielectric breakdown (CDB, also called controlled breakdown) is a method of making a nanopore in a thin insulating film by applying a voltage across it in salt water until it fails. The film is a few tens of nanometers thick or less, usually silicon nitride, and the field inside it is of the order of a volt per nanometer, close to what the material can stand. The leakage current through the film creeps up and then jumps when a conducting path forms. A circuit that watches the current cuts the voltage within about a tenth of a second, and what is left is a single pore that can be 2 nm wide or less. Harold Kwok, Kyle Briggs and Vincent Tabard-Cossa of the University of Ottawa described the method in 2014.^[1]

Earlier ways of making pores in solid membranes needed an electron microscope or an ion-beam instrument (see Nanopore fabrication), and in 2014 the authors described those two, ion-beam sculpting and drilling in a transmission electron microscope, as the only viable tools for control at the scale of 1 nm.^[1] Breakdown needs a power supply, a current meter and a liquid cell, and the pore forms already wet, in the solution where it will be used. A published protocol of 2020 reports yields above 85% in under an hour with instruments that a non-specialist can build.^[2] Molecular Reality Corporation built a research unit around the method, the Burnerphone, and later pivoted away from selling it.

Even an insulator conducts a little. Across a film 10 or 30 nm thick, at 0.4 to 1 V/nm, which is close to the breakdown strength of low-stress silicon nitride, the leakage current is attributed to trap-assisted tunneling: electrons hop from defect to defect, supplied by ions in the solution, because the film is too thick for them to tunnel straight through. The field also breaks bonds, and so makes more defects. When their density reaches a critical level they join into "a highly localized conductive path", the heat dissipated there does physical damage, and a pore opens.^[1] This is the accepted account of dielectric breakdown in thin insulators, and the exponential dependence of the time to a pore on the voltage is, in the authors' word, "reminiscent" of the time to breakdown in the gate dielectrics of transistors.^[1]

The process is a race among all the places in the film to be the first to fail, so its duration varies from pore to pore. A study of the kinetics found that the fabrication times follow a Weibull distribution, which describes a weakest-link problem, and that a difference in pH between the two sides of the membrane changes the time for a given voltage polarity.^[3] In the 2014 paper the time to a pore at a given voltage fell by a factor of 1,000 when the pH of the solution was lowered from 7 to 2. Under identical conditions it varied by a factor of 4 or so, it could be as short as a few seconds, and it did not predict the size of the pore.^[1]

The membrane is mounted between two chambers of 1 M potassium chloride, each with a silver chloride electrode. A constant voltage is applied, 5 V across a film 10 nm thick in one example and 15 V across a film 30 nm thick in another (0.5 V/nm in both), and a custom amplifier that tolerates ±20 V reads the current with a resolution below a nanoampere. The voltage is switched off when the current exceeds a threshold set at no more than 1.2 times the leakage current. That ends the stress within about 0.1 s of the breakdown, and a threshold so tight can leave pores of about 2 nm.^[1]

The pore is then measured. Its conductance gives a diameter, on the assumption that it is a cylinder and with the access resistance included, and the diameter is checked against the depth of the blockades that DNA, 2.2 nm across, makes in it. A pore sized by conductance at 6.4 nm, in a film 10 nm thick, produced blockades of 7.4 ± 0.9 nS, which with DNA as a ruler means 6.0 ± 0.5 nm.^[1] Short square pulses of ±0.2 to 0.3 V/nm applied afterward enlarge the pore with sub-nanometer precision.^[1] Cyclic pulses at high field had been shown in 2012 to set the size of a pore in situ, to lower its noise by up to three orders of magnitude and to rejuvenate pores whose electrical properties had degraded.^[4]

The pores are quiet. The 2014 paper reports low-frequency noise comparable to that of fully wetted pores drilled with an electron beam, and pores that show self-gating or rectification are conditioned with moderate pulses that widen them until the current is ohmic in high salt.^[1]

The 2014 paper made hundreds of pores from 1 to 25 nm across. It put the success rate of making a pore under its conditions above 99%, and more than 80% of the 19 pores tested detected DNA.^[1] Automating the process on films 10 nm thick gave pores no larger than 2.0 ± 0.5 nm in a sample of 23, with a mean of 1.3 ± 0.6 nm, and pores of 2.0 and 2.1 nm could tell single-stranded from double-stranded DNA.^[5] A group at Hitachi in Japan injected voltage in several levels and made pores narrower than 1 nm in a film of that thickness with a probability of 90%. It widened them to 3 nm and measured a mean effective thickness of 3.7 nm, a little over a third of the thickness of the film.^[6]

Breakdown happens where the film is weakest, so the position of the pore is random, and attempts to make pores wider than about 20 nm often give several at once.^[7] The remedies steer the failure with light. Laser heating raised the rate of breakdown in a study of single pores 20 to 50 nm across,^[7] and a bowtie-shaped plasmonic antenna on the membrane localized the breakdown to its optical hotspot, which gave a pore aligned with the antenna.^[8] At the other extreme of cost, a handheld Tesla-coil lighter made pores in 2019 when the electrolyte was replaced by water and the voltage was delivered in bursts; see Tesla coil lighter pore fabrication.^[9]

The company's Burnerphone, developed between about 2021 and 2023, was a compact unit for making pores by breakdown. Company records describe a pivot away from commercial sale because of existing patents on the method, and a decision to make pores on wafers in a central facility.^[10] A schematic sheet of the MR1 shown in a company video labels one output of the board's digital-to-analog converter "BURN".^[11] Kent Kemmish tried the lighter method for a night or two. In a post of March 2026 he wrote that one advantage over a 9-volt battery "is that it might open up making pores through membranes too thick for that approach".^[12] A 9 V battery across a film 10 nm thick gives 0.9 V/nm, inside the range of the 2014 paper.

The open design of the MR1 Nanopore Reader takes ready-made chips. Its bias circuit reaches about ±2.46 V as drawn,^[13] which across the thinnest film in its bill of materials, 10 nm thick, is 0.25 V/nm.^[14]

• Nanopore fabrication
• Solid-state nanopore
• The zapper