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Patent Issued for Cantilever, Cantilever System, and Probe Microscope and Adsorption Mass Sensor Including the Cantilever System

May 20, 2014



By a News Reporter-Staff News Editor at Journal of Technology -- From Alexandria, Virginia, VerticalNews journalists report that a patent by the inventor Shigeno, Masatsugu (Chiba, JP), filed on August 27, 2009, was published online on May 6, 2014.

The patent's assignee for patent number 8719959 is SII Nano Technology Inc. (Chiba, JP).

News editors obtained the following quote from the background information supplied by the inventors: "The present invention relates to a self-displacement detection type cantilever having high sensitivity and high resolution, a cantilever system using the cantilever, a probe microscope including the cantilever system, and an adsorption mass sensor including the cantilever system.

"In recent years, owing to progress in nanotechnology using a semiconductor process, cantilevers having leaf spring characteristics are used in various devices and sensors to conduct various measurements for shape observation, mass, viscoelasticity, magnetic force, and the like. For example, a scanning probe microscope (SPM) includes a cantilever supported in a cantilever state. A surface of a sample is scanned with a probe provided at a tip end of the cantilever. A tunnel current, an interatomic force, a magnetic force, or viscoelasticity, which acts between the probe and the sample is measured as the amount of bending (displacement) of the cantilever. Therefore, surface shapes or physical properties of the sample may be measured for imaging, and hence the cantilever is used in various fields.

"Up to now, an optical lever system for measuring a change in reflection angle of a laser beam emitted to a cantilever to obtain a displacement of the cantilever has been used as a system for detecting the amount of bending of the cantilever, that is, the displacement of the cantilever in the scanning probe microscope. In addition to an external detection method using the optical lever system, a probe microscope using a self-displacement detection type cantilever has been proposed.

"For example, a system using a piezoresistive cantilever, that is, a self-detection type SPM probe for measuring a variation in resistance value of a piezo-resistor provided on the cantilever to detect the amount of bending of the cantilever is described in JP 2000-111563 A.

"A system using a piezoelectric thin film, that is, a tunnel current detecting apparatus for detecting a fine displacement of a cantilever-shaped fine displacement element which includes the piezoelectric thin film and electrodes by the piezoelectric effect of the piezoelectric thin film is described in JP 05-190617 A.

"The self-displacement detection type cantilevers have advantages in that the structures are relatively simpler than the structure of the optical lever system and an alignment operation (operation for adjusting laser beam path) specific to the optical lever system is unnecessary.

"The conventional technologies still have the following problems.

"That is, in the case of the conventional self-displacement detection type cantilevers, there is a problem that a displacement detection signal has lower sensitivity than in the external detection method using the optical lever system and it is difficult to detect the displacement at high resolution. When high-sensitivity detection is to be performed using the conventional self-displacement detection type cantilever, a detection portion of area of 10 .mu.m unit is required. In recent years, in order to realize an increase in resonant frequency band of the cantilever and high-speed scanning, a reduction in size of the cantilever has been advanced. However, the conventional self-displacement detection type cantilevers have limitations, which is a disadvantage."

As a supplement to the background information on this patent, VerticalNews correspondents also obtained the inventor's summary information for this patent: "The present invention has been made in view of the problems described above. An object of the present invention is to provide a self-displacement detection type cantilever which has high sensitivity and high resolution and still allows reduction in size, a cantilever system using the cantilever, a probe microscope including the cantilever system, and an adsorption mass sensor including the cantilever system.

"In order to solve the problems described above, the present invention adopts the following structure. Specifically, a cantilever according to the present invention comprises: a lever portion having a leaf spring characteristic; a main body portion for supporting the lever portion at a base end side of the lever portion; and a displacement detection portion which is provided in the lever portion or between the lever portion and the main body portion and which includes at least one pair of conductor electrode portions applied with a voltage and an insulating portion sandwiched between the conductor electrode portions, the conductor electrode portions being separated at an interval for measuring one of a variation in tunnel current and an electrical change caused by the variation.

"The cantilever includes the displacement detection portion which is provided in the lever portion or between the lever portion and the main body portion and which includes at least one pair of conductor electrode portions applied with the voltage and the insulating portion sandwiched between the conductor electrode portions. The pair of conductor electrode portions are separated at the interval for measuring the variation in tunnel current or the electrical change caused by the variation, and hence the tunnel current flowing between the pair of conductor electrode portions when the voltage is applied between the pair of conductor electrode portions is varied significantly in an exponential manner with a distance between the conductor electrode portions which is changed by the displacement of the lever portion. Therefore, even when the lever portion is slightly displaced, the tunnel current flowing between the pair of conductor electrode portions significantly changes. Thus, when the variation in tunnel current or the electrical change due to the variation is measured, high-sensitivity and high-resolution detection may be realized. The displacement detection portion which is a detection portion may have a small area whose one side is approximately 5.0 nm to 0.1 .mu.m, and thus may be applied to the cantilever which is small in size and has high response characteristics.

"When the distance between the pair of the conductor electrode portions is changed with the displacement such as bending, of the lever portion, the tunnel current varies. In addition to this, even when a force is applied to the pair of conductor electrode portions by the displacement such as bending, of the lever portion, the tunnel current may be varied depending on a change in electron state. Therefore, the displacement of the lever portion may be measured also by measuring the change in electron state.

"In the cantilever according to the present invention, the conductor electrode portions and the insulating portion are laminated in the displacement detection portion, and the displacement detection portion has a laminated surface perpendicular to a virtual plane including a displacement direction of the lever portion and an extending direction of the lever portion. That is, according to the cantilever, the laminated surface of the laminated displacement detection portion is provided perpendicularly to the virtual plane including the displacement direction of the lever portion and the extending direction of the lever portion. Therefore, the lever portion is displaced within the virtual plane. Thus, a force is effectively applied to the displacement detection portion provided perpendicularly to the displacement direction of the lever portion, and hence a large variation in tunnel current may be obtained.

"Further, in the cantilever according to the present invention, the displacement detection portions are provided at at least two positions. That is, according to the cantilever, with the displacement detection portions being provided at at least two positions, when one of changes in tunnel currents of the displacement detection portions located at the difference positions is selected or the changes in tunnel currents are compared, higher-precision detection may be realized corresponding to the displacement state of the lever portion.

"Further, in the cantilever according to the present invention, the displacement detection portions are provided at a plurality of different positions in the extending direction of the lever portion. That is, according to the cantilever, with the displacement detection portions being provided at the plurality of difference positions in the extending direction of the lever portion, for not only a fundamental frequency but also a second-order or third-order resonant frequency, when the displacement detection portion located at a position suitable for the frequency is selected and the variation in tunnel current or the electrical change due to the variation is detected, the detection depending on a cantilever frequency may be achieved.

"Further, in the cantilever according to the present invention, the lever portion comprises a pair of branch support portions separately extending from a tip end side of the lever portion to the base end side thereof, and the displacement detection portions are provided to the pair of branch support portions. That is, according to the cantilever, with the displacement detection portions being provided to the pair of branch support portions, respectively, when variations in tunnel currents detected in the displacement detection portions of the respective branch support portions or electrical changes due to the variations are compared with each other, whether or not the lever portion is twisted may be detected.

"The cantilever according to the present invention further comprises a reference portion which is provided close to the lever portion and has the same structure as the displacement detection portion. That is, according to the cantilever, with the reference portion being provided close to the lever portion and having the same structure as the displacement detection portion, when a difference on the variation in tunnel current or the electrical change due to the variation is detected between the displacement detection portion and the reference portion, external factors such as a temperature, a magnetic field, and an electric field may be compensated to achieve displacement detection.

"A cantilever system according to the present invention comprises: the cantilever described above; a voltage applying portion for applying the voltage to the displacement detection portion; and a displacement detection mechanism connected to the displacement detection portion, for measuring one of the variation in tunnel current flowing between the conductor electrode portions and the electrical change caused by the variation, to detect a displacement of the lever portion. That is, with the cantilever system including the cantilever described above and the variation in tunnel current of the displacement detection portion or the electrical change due to the variation being measured by the displacement detection mechanism to detect the displacement of the lever portion, various information may be detected at high sensitivity and high resolution based on a very small displacement of the lever portion which is caused by a force applied to the lever portion.

"A probe microscope according to the present invention comprises the cantilever system described above. That is, with the probe microscope including the cantilever system described above, and with the cantilever being of a self-displacement detection type and having a cantilever structure simpler than the optical lever system, the probe microscope may measure a surface shape of an object to be measured at high sensitivity and high resolution.

"An adsorption mass sensor according to the present invention comprises the cantilever system described above. That is, with the adsorption mass sensor including the cantilever system described above, and with the cantilever being of the self-displacement detection type and having the cantilever structure simpler than the optical lever system, the adsorption mass sensor may measure the mass change that occurs when a substance to be detected is adsorbed to the tip end portion of the lever portion at high sensitivity and high resolution.

"According to the present invention, the following effects are obtained.

"Specifically, according to the cantilever and the cantilever system of the present invention, the cantilever includes the displacement detection portion which is provided in the lever portion or between the lever portion and the main body portion and which includes the at least one pair of conductor electrode portions applied with the voltage and the insulating portion sandwiched between the conductor electrode portions. The pair of conductor electrode portions are separated at the interval for measuring the variation in tunnel current or the electrical change caused by the variation. Therefore, even when the lever portion is slightly displaced, the tunnel current flowing between the pair of conductor electrode portions significantly changes. Thus, high-sensitivity and high-resolution detection may be realized. Therefore, according to the probe microscope and the adsorption mass sensor using the cantilever and the cantilever system, the cantilever is of the self-displacement detection type and has the cantilever structure simpler than the optical lever system, and hence high-sensitivity and high-resolution measurement may be realized."

For additional information on this patent, see: Shigeno, Masatsugu. Cantilever, Cantilever System, and Probe Microscope and Adsorption Mass Sensor Including the Cantilever System. U.S. Patent Number 8719959, filed August 27, 2009, and published online on May 6, 2014. Patent URL: http://patft.uspto.gov/netacgi/nph-Parser?Sect1=PTO2&Sect2=HITOFF&p=11&u=%2Fnetahtml%2FPTO%2Fsearch-bool.html&r=528&f=G&l=50&co1=AND&d=PTXT&s1=20140506.PD.&OS=ISD/20140506&RS=ISD/20140506

Keywords for this news article include: SII Nano Technology Inc..

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Source: Journal of Technology


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