CS242334B1 - A method of producing a bridge of variable ridge for radiofrequency SQUID - Google Patents

Abstract

The purpose of the invention is to ensure low-noise operation of the RF sensor in a wide temperature range with excellent mechanical resistance and durability without high material requirements for the strategically important niobium. The stated purpose is achieved by evaporating a thin aluminum layer onto a silicon substrate, provided with silicon dioxide with a shaped niobium surface for the SQUID, which is covered with a layer of positive, electron-sensitive resist. After exposure to an electron beam and development, an aluminum layer is etched in the exposed part of the resist, which serves as a mask. By etching the niobium layer in tetrafluoromethane plasma to a thickness of less than 1 pm, a bridge of variable thickness of the SQUID is formed in the aluminum gap. The invention can find wide application in cryoelectronic circuits as an extremely sensitive sensor for metrology, physical and geophysical research, in medicine for biomagnetic measurements, in microwave radiation detectors and in high-speed computers of the next generation.

Description

The purpose of the invention is to provide low noise operation of the rf sensor over a wide temperature range with excellent mechanical resistance and durability without great material requirements for a strategically important niobium.

This is accomplished by vaporizing a thin aluminum layer on a silicon-coated silica substrate with a shaped niobium surface for SQUID, which is coated with a layer of positive, electron-sensitive resist. After exposure to the electron beam and developing, an aluminum layer, which serves as a mask, is etched in the exposed part of the resist. By etching the niobium layer in tetrafluoromethane plasma to a depth of less than 1 µm, a bridge of variable depth of SQUID is formed in the aluminum gap.

The invention can find widespread use in cryoelectronic circuits as an extremely sensitive sensor for metrology, physical and geophysical jumps, medicine for biomagnetic measurements, microwave detectors, and high-speed fast computers.

The present invention relates to a method for producing a nanometer-dimensional depth-of-bridge bridge for a thin-film radio frequency superconducting quantum sensor - RF-SQUID.

Up to now, tip-type RF-SQUIDs have been used in the production of superconducting quantum magnetometers, using a massive superconductor or a thin-film RF-SQUID with a constant depth bridge. Tip sensors are material-intensive for strategically important niobium or other superconductor. Their method of preparation is very non-reproducible, requires individual machining of the tip, is sensitive to mechanical shocks, and their preparation is not compatible with the microcircuit technologies necessary for circuit integration. Thin-film constant depth bridge transducers are mechanically resistant, unmatched in weight less than tip probes, compatible with microcircuit technologies, but their great disadvantage is that they operate in a narrow temperature range, near the critical temperature of the superconductor used, resulting in increased noise and thus reduced sensor sensitivity.

The above-mentioned disadvantages are substantially eliminated by the method of manufacturing a variable depth bridge bridge for the radio frequency SQUID according to the invention, which is based on the formation of a niobium chip surface and adjustment markings for an electron lithograph on a silicon-based silica substrate. A 0.02-0.06 µm aluminum layer is applied to the structure thus prepared and covered with a 0.07-0.2 µm ₍ positive electron resist) layer. After rinsing in distilled water, the niobium layer is reactively ionically etched in tetrafluoromethane plasma to a depth of less than 0.1 µm through the formed aluminum mask in a caustic solution, preferably 1% sodium hydroxide solution.

The main advantage of the invention is that the described technological process implements a planar thin-film RF-SQUID, with a bridge of variable thickness, which due to very warm localization effect of quantum interference ensures high quality, low noise operation of the sensor in wide temperature range. as well as the possibility of optimizing coupling elements with external electronic circuits.

In the accompanying drawing, FIG. 1 illustrates a process for preparing individual sensor levels in a profile. The base silicon substrate 1 is covered with a layer of silica 2 on which a layer of niobium superconductor 3 and an electron resist 4 has been applied. 2a is a preformed electron resistor with a deposited layer of aluminum 5. FIG. 2b shows the profile of the niobium chip 6 and the deposit mark 7 for the species and the third level of electron lithography after reactive-ion etching through an aluminum mask. Fig. 3a shows a profile-shaped aluminum mask 5 through a positive electron resistor 4 in a second technological step. Fig. 3b shows the bridge portion of the sensor and 3/4 by etching the superconducting layer 8. FIG. 4 shows a side view of the entire sensor with detail A of the bridge part 8. Example

A 0.4 µm superconducting niobium layer is vapor deposited onto a 0.3 mm thick silicon mat with a 0.5 µm silica layer and covered with a 0.5 µm thick polymethyl methacrylate type electron resist. Electron lithograph exposes chip surfaces and adjustment marks. After developing the resist in a solution of methyl isobutyl ketone with isopropyl alcohol, prepare a 0,04 μπ sample with a layer of aluminum. The lift-off technique forms an aluminum mask through which a niobium layer is etched in tetrafluoromethane plasma. Remove the aluminum mask in 3% sodium hydroxide solution and rinse the sample in distilled water. The plate with chip surfaces and adjustment markings is prepared with a 0.04 µm layer of aluminum and covered with a 0.1 µm layer of polymethyl methacrylate. An electron lithograph exposes a tape of less than 0.2 μτη in the chip areas and the plate is developed in a mixture of methyl isobutyl ketone and isopropyl alcohol.

An exposed aluminum layer is etched through a gap in the polymethyl methacrylate in a 1% sodium hydroxide solution to form a gap that defines the length of the bridge of variable depth in the aluminum mask. The niobium layer is etched through the aluminum mask in tetrafluoromethane plasma to 3/4 of the flood thickness. After etching, the aluminum mask is removed in 3% sodium hydroxide solution and rinsed in distilled water. The plate is coated with 0.4 μΐη with a layer of positive electron resist to which the overall shape of the SQUlD is exposed. Once developed, 0.04 μιη of aluminum is vaporized and an etching mask is formed by the lift-off technique. In the tetrafluoromethane plasma, the niobium layer is etched in its entire thickness, resulting in a SQUID with variable bridge thickness.

The invention has a wide range of applications in cryoelectronic circuits as an extremely sensitive sensor of physical quantities transformable to magnetic fields, metrology, physical and geophysical research, medicine for biomagnetic measurement, microwave detectors, high-speed computer circuits and the like.

Claims (2)

242334 SUBJECT The manufacturing process of a SQUID variable-pitch bridge on a silicon-based silicon support with a niobium chip is characterized by the fact that the niobium chip (6J is coated with 0.02-0.06 µm aluminum layer (5 ), which is covered with 0.07 to 0.2 µm by a layer of electron positive resist (4), in which the electron-inventive lithograph produces a gap of less than 0.2 µm through which it is etched in the lye, preferably in 1 the sodium hydroxide solution, the aluminum layer and, after rinsing in distilled water, the niobium chip (6J per less than 0.1 μm) is etched in a tetrafluoromethane plasma over the formed aluminum mask. 2 sheets of drawings