JP2012242279A - Detection sensor, material detection system - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a detection sensor capable of efficiently detecting oscillation at a torsion mode.SOLUTION: A detection sensor 40 detects oscillation of an oscillator 41 in a torsion mode so as to suppress noise to perform highly sensitive detection. Here, through piezoelectrically driving the oscillator 41 by a PZT plate 130 laminated on a chip package 120, signal detection is performed with detection elements 45A to 45D comprising p-type semiconductor piezo resistance elements formed on an oscillator chip 100, so that the detection sensor 40 can be made very compact.

Description

  The present invention relates to a detection sensor and a substance detection system capable of detecting a substance such as VOC (Volatile Organic Compounds).

  Conventionally, there are sensors for detecting the presence of various substances and odors in the air, or their quantitative concentrations. In this sensor, the presence or absence of a specific substance or the concentration thereof is detected by adsorbing a specific type of molecule contained in the gas and detecting the presence or absence or the amount of adsorption.

A sensor element that detects molecules floating in the air by their minute molecular mass vibrates the vibrator in a gas containing these molecules, and the mass change of the vibrator when molecules are attached or adsorbed to the vibrator surface Is detected as a change in the vibration characteristics of the vibrator.
As a vibrator that performs mass detection in this way, there is a cantilever-type vibrator that utilizes the vibration of a cantilever (see, for example, Patent Documents 1 to 3). Such a cantilever type vibrator is manufactured in a micrometer (micrometer) unit area by using a technology called MEMS (Micro Electro Mechanical Systems) that precisely processes a silicon thin film or the like by photographic technology (photolithography). It has become possible to do. By reducing the size of the vibrator, the mass of the vibrator is greatly reduced, and the detection sensitivity for the attached mass is improved.

Here, when performing detection in a cantilever type vibrator, in order to vibrate (drive) the vibrator, various piezoelectric materials are used on the surface of the vibrator formed of a silicon-based material such as SiO ₂ (silicon dioxide). A piezoelectric element and an electrode layer made of metal are provided. Then, the vibrator is vibrated by applying a voltage from the electrode layer to the piezoelectric element, and the change in the resonance frequency is monitored.

In a sensor using such a cantilever type vibrator, it is always required to increase its detection sensitivity.
Here, as shown in FIG. 11A, the cantilever-type vibrator 300 has a fixed end 300a and a free end 300b on the free end 300b side with respect to the fixed end 300a side because of easy installation of the driving device. It was common to oscillate in a bending mode so as to be deformed so as to be displaced in the direction connecting the two and the direction perpendicular to the surface (construction surface) of the cantilever. However, in the bending mode, since the Q value indicating the quality of resonance is about 1000, the short-time standard deviation of the frequency increases for the same phase noise, and the minimum detection limit does not decrease.

  On the other hand, as shown in FIG. 11B, it is also proposed to drive the cantilever-type vibrator 300 in a twist mode in which the cantilever-type vibrator 300 is deformed so as to be twisted in the circumferential direction around the direction connecting the fixed end 300a and the free end 300b. (For example, refer nonpatent literature 1). Here, a PZT actuator is used to drive the vibrator 300, and an optical method is used to detect a change in vibration frequency of the vibrator.

Non-Patent Document 2 discloses that a vibrator in a twist mode is generated by electromagnetically driving a cantilever vibrator.
For cantilever type vibrators that generate torsional mode vibration, rectangular piezoresistive elements are placed at an angle of 45 degrees from the fixed end to the free end of the cantilever, and the resistance change of these piezoresistive elements is measured Vibration is detected.

JP 2001-56278 A JP 2009-133772 A JP 2005-148062 A

B.R.Kim, F.E.Prins, D.P.Kern, S. Raible, U. Weimar [Multicomponent analysis and prediction with a cantilever array based gas sensor] Sensors and Actuators B 78 (2001) 12-18 JIN Dazhong, LI Xinxin, BAO Hanhan, ZHANG Zhixiang, WANG Yuelin, YU Haitao, ZUO Guomin, D. Jin, X. Li, H. Bao, Z. Zhang, Y. Wang, H. Yu, G. Zuo [Integrated cantilever sensors with a torsional resonance mode for ultraresoluble on-the-spot bio / chemical detection] Applied Physics letters Vol.90, No.4, Page.041901-041901-3 (2007.01.22)

However, in the sensor using the vibrator as described above, higher sensitivity is always required. For this purpose, as described above, it is effective to greatly reduce the mass of the vibrator by reducing the size of the cantilever vibrator to the μm unit and improve the detection sensitivity with respect to the adhered mass. As a result, the detection sensor can be greatly reduced in size.
On the other hand, as described in Non-Patent Documents 1 and 2, an optical method was used to detect a change in vibration frequency of a vibrator that vibrates in a torsion mode, or an electromagnetic drive was used to drive the vibrator. However, there is a problem that even if the drive system and the detection system are enlarged and the vibrator itself is small, the entire detection sensor is large.
The present invention has been made based on such a technical problem, and an object of the present invention is to provide a small detection sensor and substance detection system with high sensitivity.

The detection sensor of the present invention made for such an object includes a vibrator having a beam shape in which one end is fixed to a substrate and the other end is a free end, and a vibrator A piezoelectric element that vibrates the piezoelectric element, an element package that applies a voltage to the piezoelectric element, and a vibration detection unit that detects vibration of the vibrator. A pair of strain sensors for detection arranged side by side and a pair of strain sensors for reference provided on a substrate, and at least one of the strain sensors for detection is disposed at an end in the width direction of the vibrator. The vibration detection unit is provided to detect at least vibration in a twist mode of the vibrator.
In this way, the vibrator is vibrated by the piezoelectric element, and at least the vibration of the torsional mode of the vibrator is detected by the strain sensor, so that the detection sensor is highly sensitive while being highly sensitive. Can do.

  Such a detection sensor may be used for any application, but further includes a sensitive film that adsorbs a gas on the vibrator, and the vibrator changes its vibration characteristics due to adsorption of a substance having mass. It can also be detected by a vibration detector. Thereby, adsorption | suction of the substance to a sensitive film | membrane can be detected with high precision.

Here, the pair of strain sensors for detection are provided at one end and the other end in the width direction of the vibrator, and the vibration detector can detect the torsional mode vibration of the vibrator. it can.
The pair of strain sensors for detection are provided at one end in the width direction of the vibrator and at the center in the width direction of the vibrator, and the vibration detection section has a twist mode and a bending mode of the vibrator. Vibrations can also be detected.
Note that the detection strain sensors may be a pair of two, or may be a pair of four, eight, or the like.

  Furthermore, in the vicinity of the base end of the vibrator, at least three detection strain sensors are provided at both ends in the width direction of the vibrator and in the middle in the width direction, and at one end in the width direction of the vibrator. The detection strain sensor provided and the detection strain sensor provided at the other end in the width direction of the vibrator constitute a pair of detection strain sensors. A detection strain sensor provided at one end in the width direction of the vibrator and a detection strain sensor provided in the middle part in the width direction of the vibrator. The strain sensor is configured, and the vibration detection unit can detect the vibration in the bending mode of the vibrator.

  Here, a piezoelectric element is bonded to one surface side of the element package, and a substrate having a vibrator is laminated and bonded to the piezoelectric element, and the substrate and the piezoelectric element are only at the four corners of the piezoelectric element or two opposite sides. It is preferable to join using an adhesive. Thereby, the vibrator can be efficiently driven in the torsion mode.

  The sensitive film is preferably any of polybutadiene (PBD), polyacrylonitrile-butadiene (PAB), polyisoprene (PIP), and polystyrene (PS).

  The present invention is a substance detection system that detects at least one of the type and concentration of a specific substance contained in a gas to be detected, and introduces the gas to be detected into the system and transports the introduced gas in the system. A beam to be used, a suction part that adsorbs a specific substance contained in the gas introduced into the system by the pump, a fixed end fixed to the substrate at one end, and a free end at the other end A vibrator whose vibration characteristics change due to adhesion or adsorption of a substance having a mass, a sensitive film that adsorbs a gas, a piezoelectric element that vibrates the vibrator, an element package that applies a voltage to the piezoelectric element, and vibration A vibration detection unit that detects the vibration of the child, and the vibration detection unit is provided on the substrate and a pair of detection strain sensors arranged in the width direction of the vibrator in the vicinity of the fixed end of the vibrator. Pair A strain sensor for reference, and at least one of the strain sensors for detection is provided at an end portion of the vibrator in the width direction with respect to the center of the vibrator in the width direction, and vibration in a torsion mode of the vibrator Among the vibrations in the bending mode, at least the torsional mode vibration can be detected.

In this case, a plurality of vibrators are provided, and whether each of the plurality of vibrators is detected in one of the torsion mode and the bending mode is set in advance. preferable.
Thereby, it is possible to perform detection in different vibration modes in a plurality of sets of vibrators.

According to the present invention, highly sensitive detection is possible by performing detection by vibrating a vibrator in a torsional mode.
In addition, the detection sensor can be made very small by driving the vibrator with the piezoelectric element and detecting the torsional mode vibration of the vibrator with the strain sensor.
In this way, a small but highly sensitive detection sensor can be realized.

It is a figure which shows the structure of the substance detection system in this Embodiment. It is sectional drawing and a perspective view which show the drive mechanism of a vibrator | oscillator. It is a figure which shows the laminated structure of a PZT board and a chip package. It is a figure which shows the structure of the vibration detection part of the vibrator | oscillator in 1st embodiment, (a) is the example of arrangement | positioning of a detection element, (b) is a circuit diagram of the Wheatstone bridge for detecting a vibration, (c). Is a layout example on a substrate. It is a figure which shows the structure of the vibration detection part of the vibrator | oscillator in 2nd embodiment, (a) is the example of arrangement | positioning of a detection element, (b) is a circuit diagram of the Wheatstone bridge for detecting a vibration, (c). Is a layout example on a substrate. It is a figure which shows the structure of the vibration detection part of the vibrator | oscillator in 3rd embodiment, (a) is the example of arrangement | positioning of a detection element, (b) is a circuit diagram of the Wheatstone bridge for detecting the vibration of torsion mode, (C) is a circuit diagram of a Wheatstone bridge for detecting bending mode vibrations. It is a figure which shows the relationship between the frequency when a vibration is applied to a vibrator chip, and the amount of displacement. It is a figure which shows the time change of the resonance frequency standard deviation in a bending mode and a twist mode. It is a figure which shows the dependence to the film thickness of the sensitive film | membrane of the system minimum detection limit. It is a figure which shows the temperature dependence of the system minimum detection limit. It is a figure which shows a bending mode and a twist mode.

Hereinafter, the present invention will be described in detail based on embodiments shown in the accompanying drawings.
[First embodiment]
FIG. 1 is a diagram for explaining the overall configuration of a substance detection system 10 in the present embodiment.
The substance detection system 10 shown in FIG. 1 adsorbs specific types of molecules to be detected, thereby detecting the presence or absence (occurrence) of the gas itself or a plurality of types of specific substances or odors contained in the gas, or The concentration is detected.
The substance detection system 10 sucks in a gas to be detected contained in a sample container 15 and generates a gas flow in the system, an adsorption unit 30 that adsorbs the gas sucked in the pump 20, and an adsorption Based on the detection sensor 40 that adsorbs a specific type of molecule contained in the gas component from the gas adsorbed by the unit 30 and outputs a detection signal corresponding to the adsorption of the molecule, And a measurement processing unit (detection unit) 50 that measures the presence or absence of the species of molecules or the amount thereof.

The adsorbing unit 30 is filled with, for example, carbon fiber as an adsorbing body inside a cylindrical cylindrical body 31 made of stainless steel, for example. Of course, other adsorbents can be used as appropriate. The gas discharged from the pump 20 is sent into the cylinder 31 and comes into contact with the adsorbent so that the component molecules in the gas are adsorbed to the adsorbent by physical adsorption with low selectivity.
A sheath heater (heater) 34 is wound around the outer peripheral surface of the cylindrical body 31. By applying a voltage to the sheath heater 34, the component molecules adsorbed on the adsorbent are desorbed, and the component molecules are conveyed to the detection sensor 40 by the flow generated by the pump 20.

  As shown in FIG. 2, the detection sensor 40 has a cantilever type cantilever type in which a base end portion 41a is fixed and the other end portion 41b is a free end. And a sensitive film 42 that is formed on the surface of 41 and adsorbs molecules desorbed by the adsorption unit 30.

  The sensitive film 42 has a property of adhering or adsorbing a gas to be detected, but a specific gas is selected for polybutadiene (PBD), polyacrylonitrile-butadiene (PAB), polyisoprene (PIP), and polystyrene (PS). It has been clarified by the present inventors' research that it has a selective property to adhere to or adsorb. In addition, examples of materials that can be employed as the sensitive film 42 include metal complexes such as phthalocyanine derivatives and porphyrin derivatives, conductive polymers such as polythiophene and polyaniline, and inorganic materials such as a titanium oxide porous film.

  Polyacrylonitrile-butadiene (PAB) has selectivity for gases such as octane and propanol. Polybutadiene (PBD) and polyisoprene (PIP) have selectivity for toluene. Polystyrene (PS) has selectivity for n-propanol and ethanol.

  The vibrator 41 on which the sensitive film 42 as described above is formed is provided in a chamber having a predetermined volume (for example, 0.1 to 0.5 cc). In the chamber, a plurality of vibrators 41 each having the sensitive film 42 as described above are installed. Different sensitive films 42 are formed on the plurality of vibrators 41.

Now, a driving structure of the vibrator 41 of the detection sensor 40 in the substance detection system 10 as described above will be described.
The vibrator 41 uses, for example, a piezoelectric drive system as a drive source, and vibrates the vibrator 41 at a predetermined frequency.
As shown in FIG. 2, the vibrator 41 is formed on a vibrator chip (substrate) 100 made of a silicon-based material. The vibrator 41 is formed by patterning the vibrator chip 100 by a photolithography method or the like and removing unnecessary portions by etching or the like, and is a fixed end in which the base end portion 41a is fixed to the substrate body 101. The other end 41b is an overhang free end.

  In the present embodiment, torsional mode vibration of the vibrator 41 is detected. When the resonance frequency of the vibrator 41 in the torsion mode is a high frequency of, for example, 1 MHz or more, handling at the time of detection becomes difficult due to the influence of the parasitic capacitance between the electrodes. Therefore, it is preferable to form the vibrator 41 so that the resonance frequency of the vibrator 41 in the torsional mode is between 400 kHz and 1 MHz. Therefore, the vibrator 41 preferably has a width of about 50 to 120 μm and a length of about 300 to 420 μm, for example.

  Such a transducer chip 100 is supported on a base substrate 110 serving as a base of the detection sensor 40 via a chip package (element package) 120 and a PZT plate (piezoelectric element) 130.

  The chip package 120 is provided on one surface side of the base substrate 110 with an outer peripheral portion fixed by a fixing member 112. The chip package 120 can mount an IC chip and has a wiring pattern that is electrically connected to each electrode of the IC chip. As such a chip package 120, DIP (Dual Inline Package) or QFP (Quad Flat Package) can be used.

The PZT plate 130 is a plate-like body made of a PZT material, and is bonded to one surface side of the chip package 120 via an adhesive 200.
The PZT plate 130 is arranged with the positive electrode on the chip package 120 side and the negative electrode on the vibrator chip 100 side. Each electrode of the PZT plate 130 is electrically connected to the wiring portion of the chip package 120 by a wiring 140 by wire bonding. The PZT plate 130 generates vibration at a predetermined frequency by a voltage applied from the chip package 120 in accordance with a control signal from an external drive circuit.

In the resonator chip 100, the substrate body 101 is bonded to the other surface side of the PZT plate 130 with an adhesive 210.
Further, in order to efficiently transmit the vibration generated in the PZT plate 130 to the vibrator chip 100, the PZT board 130 and the vibrator chip 100 have a high hardness (rigidity) after being hardened to the adhesive 210, for example, an epoxy system, for example. It is preferable to use an adhesive or the like to firmly integrate. The adhesive 210 can suppress the vibration transmitted from the PZT plate 130 to the transducer chip 100 from being attenuated.

On the other hand, it is preferable to join the chip package 120 and the PZT plate 130 so that the vibration generated in the PZT plate 130 is not inhibited by the chip package 120. For this reason, as the adhesive 200, for example, a silicone adhesive (silicone resin adhesive) having a lower hardness (rigidity) after curing than the adhesive 210 that joins the PZT plate 130 and the transducer chip 100, for example. It is preferable to use it.
Further, instead of bonding the entire surface of the PZT plate 130 to the chip package 120, as shown in FIGS. 3 (a) and 3 (b), the chip is formed by the adhesive 200 at a part of the PZT plate 130, for example, at the four corners. -Adhere to the package 120. As the adhesive 200, it is preferable to use a non-conductive material having some elasticity such as a silicone-based adhesive. In addition, since the adhesive 200 is non-conductive, a conductive material such as a silver paste or a metal-containing adhesive is provided between the PZT plate 130 and the chip package 120 in a portion other than the portion bonded by the adhesive 200, for example, in the central portion. The PZT plate 130 and the chip package 120 are electrically connected with the conductive material 220 interposed.
Further, as shown in FIG. 3 (c), one end side 130a of the PZT plate 130 is bonded with a hardened epoxy adhesive or the like as the adhesive 200, and the other end side 130b of the PZT plate 130 is connected. Alternatively, the adhesive 200 may be joined by a silicone adhesive having a low hardness after curing. Thus, the PZT plate 130 has a cantilever shape in which one end side 130a is a fixed end and the other end side 130b is a free end. According to such a support structure of the PZT plate 130, as shown in FIGS. 3A and 3B, the PZT plate 130 has a vibration mode as compared with the case where the PZT plate 130 is fixed at, for example, four corners. Accordingly, it becomes possible to vibrate more freely.

  In the above description, the hardness of the adhesives 200 and 210 is referred to, but this is between the adhesive 200 and the adhesive 210 or the adhesive 210 on one end side of the PZT plate 130 and the adhesive 210 on the other end side. It is hard and soft on the relative comparison between. Accordingly, it goes without saying that other types of adhesives than those described above, or other joining means may be used.

As shown in FIG. 4A, the vibrator 41 includes a vibration detection unit 44 for detecting a change in its own vibration state (vibration frequency) as an electric signal. The vibration detection unit 44 can be realized by, for example, a p-type semiconductor piezoresistive element.
In the present embodiment, the vibration detection unit 44 includes detection elements 45A to 45D including four p-type semiconductor piezoresistive elements. Among these detection elements 45A to 45D, detection elements (detection strain sensors) 45A and 45B are provided on the vibrator 41, and detection elements (reference strain sensors) 45C and 45D are vibrators in the vicinity of the vibrator 41. Provided on the chip 100. Then, while detecting the vibration displacement of the vibrator 41 by the detection elements 45A and 45B, the detection elements 45C and 45D are used for reference, and the difference between the signal and the detection elements 45C and 45D is taken to remove the noise and detect it. Can be done.

Detection elements 45 </ b> A and 45 </ b> B for detection are provided offset at both ends on one side and the other side in the width direction of the vibrator 41. Here, the detection element 45 </ b> A and the detection element 45 </ b> B are provided so as to be symmetric with respect to the center of the vibrator 41 in the width direction.
The detection elements 45A and 45B can detect the torsional mode with higher sensitivity as the position of the transducer 41 from the center in the width direction is further away. The detection elements 45 </ b> A and 45 </ b> B have a distance d from the center in the width direction of the vibrator 41 with respect to the width w of the vibrator 41
d> 0.25w
It is preferable to install so that it becomes.
Here, in the vibrator 41, the stress due to the torsional mode vibration becomes maximum at the base end portion 41a. Therefore, the detection elements 45A and 45B are preferably provided at the proximal end portion 41a of the vibrator 41.

  The detection elements 45 </ b> A to 45 </ b> D have a stress dependency of resistance change with respect to the crystal orientation of the silicon-based material forming the vibrator 41. The p-type semiconductor piezoresistive element that constitutes the detection elements 45A to 45D formed by doping the surface of the vibrator 41 with p-type impurities is the vibrator 41 when the current is taken in the <110> direction of the crystal orientation. The maximum piezoresistance coefficient is obtained, and the maximum voltage change is obtained. Accordingly, it is preferable to form the vibrator 41 and the detection elements 45A to 45D so that the current flow direction in the detection elements 45A to 45D and the longitudinal direction of the vibrator 41 coincide with the crystal orientation <110> direction.

And these detection elements 45A-45D are provided so that a Wheatstone bridge circuit as shown in FIG.4 (b), (c) may be comprised.
In such a vibration detection unit 44, the detection elements 45A and 45C are connected in series, and the detection elements 45B and 45D are connected in series. Then, a potential difference V between the intermediate voltage between the detection element 45A and the detection element 45C and the intermediate voltage between the detection element 45B and the detection element 45D is detected.
This potential difference V is expressed as follows.
V = Vs × (ΔRa−ΔRb) / R
Here, ΔRa is a resistance change in the detection element 45A, ΔRb is a resistance change in the detection element 45B, R is a resistance value of the detection elements 45A to 45D when receiving no stress, and Vs is a voltage applied to the Wheatstone bridge.

  With such a circuit configuration, the rotation of the proximal end portion 41a of the vibrator 41 in the circumferential direction around the axis connecting the proximal end portion 41a and the distal end portion of the vibrator 41, that is, the rotational displacement in the torsion mode. Can be detected. At this time, ΔRa is a resistance change in the detection element 45A, and ΔRb is a resistance change in the detection element 45B. If these are added, ΔRa and ΔRb are opposite in sign (the generated stress is in the opposite direction), that is, the absolute value of the displacement on one side in the width direction of the vibrator 41 and the absolute value of the displacement on the other side. It is possible to detect the frequency change with double the sensitivity.

As shown in FIG. 1, the measurement processing unit 50 includes a drive circuit 51 for driving the vibrator 41 as described above and a detection circuit 52 for detecting an electrical signal from the vibration detection unit 44. Yes.
An object to be detected such as a molecule having a mass in the sensitive film 42 in a state where the vibrator 41 of the detection sensor 40 is driven by an electric signal from the drive circuit 51 and vibrates at a predetermined frequency under the control of a control unit (not shown). Is attached, the vibration frequency of the vibrator 41 changes. The detection circuit 52 of the measurement processing unit 50 receives the electric signal output from the vibration detection unit 44 and detects the change in the electric signal to detect whether or not a specific type of molecule is adsorbed on the sensitive film 42 or its amount. Measure.
The measurement result in the measurement processing unit 50 can be output on the display unit 53 by ON / OFF of lamps, buzzers, etc., display of measured values, measurement levels, display of detection substance name / concentration (amount), and the like. preferable.

In this way, the substance contained in the gas can be identified and its concentration can be measured. At this time, by detecting the torsional mode vibration of the vibrator 41, noise can be suppressed and detection with higher sensitivity can be performed.
At this time, the vibrator 41 is piezoelectrically driven by the PZT plate 130 laminated on the chip package 120, and signal detection is performed by the detection elements 45A to 45D made of p-type semiconductor piezoresistive elements formed on the vibrator chip 100. The detection sensor 40 can be made very small.
In this way, it is possible to realize a detection sensor 40 that is small but highly sensitive.

  Further, the discriminating ability is enhanced by providing a plurality of vibrators 41 and making the materials of the sensitive film 42 in the plurality of vibrators 41 different from each other. Further, by detecting the desorption timing when the substance is desorbed from the adsorbent by the heating of the sheath heater 34 with the detection sensor 40 and the measurement processing unit 50, the ability to identify the type of the substance is enhanced.

[Second Embodiment]
Next, a second embodiment of the detection sensor according to the present invention will be described.
In the second embodiment described below, the configuration of the vibration detection unit 44 is different from that of the first embodiment, and other configurations are the same as those of the first embodiment. Therefore, in the following description, the configuration different from that of the first embodiment will be mainly described, and the components common to the first embodiment will be denoted by the same reference numerals and the description thereof will be omitted.

  As shown in FIG. 5, in the substance detection system 10 of this embodiment, the vibration detection unit 44 for detecting a change in the vibration state (vibration frequency) of the vibrator 41 as an electric signal includes four p-type semiconductors. Detection elements 46A to 46D each including a piezoresistive element are provided. Among these detection elements 46A to 46D, detection elements (detection strain sensors) 46A and 46B are provided on the vibrator 41, and detection elements (reference strain sensors) 46C and 46D are vibrators in the vicinity of the vibrator 41. Provided on the chip 100.

Of the detection elements 46 </ b> A and 46 </ b> B for detection, one detection element 46 </ b> A is offset from the end portion on one side in the width direction of the transducer 41. The other detection element 46B is provided in the vicinity of the center of the vibrator 41 in the width direction.
The detection element 46A can detect the torsional mode with higher sensitivity as the position of the transducer 41 from the center in the width direction becomes farther. The detection element 46A has a distance d from the center in the width direction of the vibrator 41 with respect to the width dimension w of the vibrator 41.
d> 0.25w
It is preferable to install so that it becomes.
The position of the detection element 46B may be the center in the width direction of the vibrator 41, but may be provided on the other side from the center in the width direction with an offset dimension smaller than the offset dimension of the detection element 46A. The detection element 46B is arranged closer to the center, and the distance d from the center of the vibrator 41 in the width direction is smaller than the width dimension w of the vibrator 41.
d <0.25w
It is preferable to install so that it becomes.
Also in this case, in the vibrator 41, the stress caused by the vibration in the torsion mode and the bending mode is maximized at the base end portion 41a. Therefore, the detection elements 46A and 46B are provided at the base end portion 41a of the vibrator 41. Is preferred.

And these detection elements 46A-46D are provided so that a Wheatstone bridge circuit as shown in FIG.5 (b), (c) may be comprised.
In such a vibration detection unit 44, the detection elements 46A and 46C are connected in series, and the detection elements 46D and 46B are connected in series, whereby the detection elements 46A and the detection elements 46C are arranged diagonally. Then, a potential difference V between the intermediate voltage between the detection element 46A and the detection element 46C and the intermediate voltage between the detection element 46D and the detection element 46B is detected.
This potential difference V is expressed as follows.
V = Vs × (ΔRa + ΔRb) / R

  With such a circuit configuration, the detection element 46B rotates the base end 41a of the vibrator 41 in the circumferential direction around the axis line connecting the base end 41a and the tip of the vibrator 41, that is, The rotational displacement of the torsional mode vibration can be detected as ΔRb. In the torsion mode, the stress at the center of the vibrator is almost 0, and ΔRa˜0. Further, in the bending mode vibration in which the distal end portion is displaced in the direction perpendicular to the axis of the transducer 41 and the surface of the transducer 41 by the detection element 46A, ΔRa = ΔRb is obtained. The vibration displacement can be detected with about twice the sensitivity. In this way, both the bending mode and the torsion mode can be detected.

[Third embodiment]
Next, a third embodiment of the detection sensor according to the present invention will be described.
In the third embodiment described below, the configuration of the vibration detection unit 44 is different from those of the first and second embodiments, and other configurations are the same as those of the first and second embodiments. . Therefore, in the following, the description will be focused on the configuration different from the first and second embodiments, and the same reference numerals will be given to the configurations common to the first and second embodiments, and the description thereof will be omitted. To do.

  As shown in FIG. 6, in the substance detection system 10 of the present embodiment, the vibration detection unit 44 for detecting a change in the vibration state (vibration frequency) of the vibrator 41 as an electric signal includes four p-type semiconductors. Detection elements 47A to 47F made of piezoresistive elements are provided. Among these detection elements 47A to 47F, detection elements (detection strain sensors) 47A, 47B, and 47C are provided on the vibrator 41, and detection elements (reference strain sensors) 47D, 47E, and 47F are provided on the vibrator 41. It is provided in a nearby transducer chip 100.

Of the detection elements 47A, 47B, and 47C for detection, the detection element 47A is provided offset to an end portion on one side in the width direction of the vibrator 41. The detection element 47B is provided near the center of the vibrator 41 in the width direction. The detection element 47 </ b> C is offset from the other end in the width direction of the vibrator 41.
The detection elements 47A and 47C can detect the torsional mode with higher sensitivity as the position of the transducer 41 from the center in the width direction becomes farther. The detection elements 47A and 47C have a distance d from the center in the width direction of the vibrator 41 with respect to the width dimension w of the vibrator 41.
d> 0.25w
It is preferable to install so that it becomes.
The position of the detection element 47B may be the center in the width direction of the vibrator 41, but may be provided on the other side from the center in the width direction with an offset dimension smaller than the offset dimension of the detection element 47A. The detection element 47B has a distance d from the center in the width direction of the vibrator 41 with respect to the width dimension w of the vibrator 41.
d <0.25w
It is preferable to install so that it becomes.
Also in this case, in the vibrator 41, the stress due to the torsional mode and bending mode vibrations is maximized at the base end portion 41a, so that the detection elements 47A and 47B are applied to the base end portion 41a of the vibrator 41. It is preferable to provide it.

And these detection elements 47A-47F are provided so that the Wheatstone bridge circuit as shown in FIG.6 (b), (c) may be comprised.
In such a vibration detection unit 44, the detection elements 47A and 47D are connected in series, the detection elements 47B and 47E are connected in series, and the detection elements 47C and 47F are connected in series.
Then, the Wheatstone bridge circuit as shown in FIG. 6B is configured by the detection elements 47A and 47D and the detection elements 47C and 47F at both ends of the vibrator 41, and the detection element 47B near the center of the vibrator 41 is formed. , 47E and detection elements 47C and 47F, the detection elements 47A to 47F are connected as shown in FIG. 6A so as to form a Wheatstone bridge circuit similar to that shown in FIG.
When detecting the torsional mode vibration, the torsional mode differential amplifier 60A for extracting the intermediate voltage of the detection elements 47A and 47D and the intermediate voltage of the detection elements 47C and 47F is used to detect the bending mode vibration. At the time of detection, a bending mode differential amplifier 60B that extracts the intermediate voltage of the detection elements 47C and 47F and the intermediate voltage of the detection elements 47E and 47B is used.
Switching between the torsional mode differential amplifier 60A and the bending mode differential amplifier 60B is performed by the measurement processing unit 50 by performing switching control of a switch (not shown).

In such a vibration detection unit 44, the torsion mode vibration and the bending mode vibration of the vibrator 41 are switched by switching between the torsion mode differential amplifier 60A and the bending mode differential amplifier 60B. Can be selectively detected.
For this purpose, the measurement processing unit 50 sets in advance whether the vibrator 41 detects in the torsion mode or the bending mode, and performs detection in the set mode.
If the frequency of vibration to be detected is low, the measurement temperature is low, or the material of the vibrator 41 is hard, detection can be performed with necessary and sufficient sensitivity even in the bending mode. On the other hand, when the frequency of vibration to be detected is high (that is, when the natural frequency of the vibrator 41 is high), when the measurement temperature is high, or when the sensitive film material applied to the vibrator 41 is soft, detection by the bending mode is performed. It can be said that the detection in the torsion mode tends to be more sensitive than the detection.
Therefore, it is possible to select which one of the bending mode and the torsion mode is used according to these conditions.

  In the configuration as described above, in particular, when a plurality of transducers 41 are provided, it is possible to detect a substance by selecting a detection mode in advance for each transducer 41.

[Example]
Simulation analysis and examination experiments were performed on the detection sensor as described above, and the results are shown below.
First, a cantilever type vibrator having a width of 100 μm × length of 500 μm × thickness of 5 μm was fixed to a part of an upper portion of a 6 mm square and 0.5 mm thick PZT plate, and three corners of the PZT plate were fixed. A forced vibration having an amplitude Z0 was applied to the remaining corner, and the displacement state of the vibrator surface was measured by a two-dimensional displacement measuring device (Policic Japan MSA-500).
As a result, as shown in FIG. 7, it was confirmed that the vibrator vibrates with a complicated vibration mode, and the displacement of other components appears in addition to the vertical direction.

After forming a PAB film with a film thickness of 820 nm or 1080 nm with excellent adsorption characteristics to acetone or alcohol as a sensitive film on the upper surface of a cantilever type vibrator having a width of 50 μm × length of 200 μm × thickness of 5 μm using a dispenser Created by drying.
The vibrator used as the mass sensor was manufactured from an SOI wafer having an active layer having a thickness of 5 μm. The active layer is an n-type having an impurity concentration of 1 × 10 ¹⁵ / cm ³ , and a vibrator structure having a width of 50 to 100 μm and a length of 200 to 500 μm is formed by using Deep Reactive Ion Etching (DRIE). In order to suppress air damping of the vibrator, the substrate was removed from the back surface by DRIE. The BOX layer on the back surface of the vibrator was finally removed by BHF etching.
A piezoresistive element for vibration detection was formed at the base on the front side of the vibrator, and a Cr (10 nm) / Au (100 nm) film for coating a detection film was formed on the other main body. The piezoresistor is made of B ion implanter, p-type with an impurity concentration of 1 × 10 ¹⁸ / cm ³ , and has a depth of about 1 μm. In order to make ohmic contact with the metal wiring, the contact portion was doped with a high-concentration p-type impurity (1 × 10 ¹⁹ / cm ³ , depth of about 0.3 μm). Then, an Al—Si—Cu alloy wiring was formed through a passivation oxide film having a thickness of 500 nm.
Further, a sensitive film was formed on the surface of the vibrator by applying PAB to a thickness of 820 nm.

In such a vibrator, the mode dependency of short-time frequency change (phase noise) when the vibrator was oscillated at the resonance frequency using the measurement processing unit 50 was examined.
As shown in FIG. 8A, when the vibration in the second bending mode was generated at a frequency of about 900 kHz, the standard deviation of the short-time frequency change was 0.55 Hz. On the other hand, as shown in FIG. 8B, when the vibration in the torsional mode having the frequency of 1286 kHz is generated, the standard deviation of the short-time frequency change is 0.09 Hz, which is approximately 1/9 compared with the bending mode. It was confirmed that the influence of phase noise was reduced.

Next, the system minimum detection limit concentration when the thickness of the sensitive film applied to the vibrator was varied was compared. The system minimum limit concentration was defined as a value obtained by dividing 3 times the standard deviation by the sensitivity, as in the formula in the figure. Here, the coefficient 1000 is the conversion from ppm to ppb, and the coefficient 50 is the concentration rate when 1000 cm ³ is concentrated by the concentrator of this system.
there,
Sensitive film thickness: 1030 nm, width 50 μm × length 300 μm vibrator (1) when driven in a bending mode of about 400 kHz and (2) when driven in a twisting mode of about 550 kHz,
The film thickness of the sensitive film: 810 nm, width 50 μm × length 200 μm was compared between (3) driving in 900 kHz bending mode and (4) driving in 1286 kHz twist mode.
Further, the minimum system detection limit concentration when a bending mode of about 800 kHz is driven for a vibrator having a sensitive film thickness of 320 nm, 630 nm, 1060 nm, 1420 nm, width 100 × length 500 μm is shown by a curve in FIG.
As a result, as shown in FIG. 9, in the comparison between the conditions (1) and (2) and the conditions (3) and (4), the torsional mode has a minimum system detection limit concentration in any case. It was confirmed to be significantly lower. As a result, it was confirmed that if the thickness of the sensitive film is large, high sensitivity can be achieved by adopting the torsion mode.

Moreover, the system minimum detection limit density | concentration when the detection atmosphere temperature was varied was compared.
Sensitive film thickness: 1030 nm, width 50 μm × length 300 μm vibrator at a measurement temperature of 23 ° C. (5) when driven in a bending mode of about 400 kHz and (6) when driven in a twisting mode of about 550 kHz Comparison with
Sensitive film thickness: 810 nm, width 50 μm × length 200 μm vibrator at (7) 900 kHz bending mode and (8) 1286 kHz torsion mode at a measurement temperature of 20 ° C. A comparison was made.
FIG. 10 shows the minimum system detection limit concentration when a sensitive film thickness of 620 nm, a width of 100 μm × length of 500 μm is driven in a bending mode of about 800 kHz at measurement temperatures of 5 ° C., 15 ° C., and 25 ° C. Is shown by a curve.
As a result, as shown in FIG. 10, it was confirmed that the higher the measured temperature, the higher the sensitivity can be achieved by adopting the torsion mode.

  The configuration described in the above embodiment is merely an example, and the configuration described in the above embodiment may be selected or changed to another configuration as long as it does not depart from the gist of the present invention. Is possible.

DESCRIPTION OF SYMBOLS 10 Substance detection system 15 Sample container 20 Pump 30 Adsorption part 31 Cylindrical body 34 Sheath heater (heater)
DESCRIPTION OF SYMBOLS 40 Detection sensor 41 Vibrator 41a Base end part 41b Other end part 42 Sensitive film | membrane 44 Vibration detection part 45A-45B, 46A-46B, 47A-47C Detection element (distortion sensor for a detection)
45C-45D, 46C-46D, 47D-47F Detection element (reference strain sensor)
DESCRIPTION OF SYMBOLS 50 Measurement processing part 51 Drive circuit 52 Detection circuit 53 Display part 60A Torsional mode differential amplifier 60B Bending mode differential amplifier 100 Vibrator chip 101 Substrate body 110 Base substrate 112 Fixing member 120 Chip package (element package)
130 PZT plate (piezoelectric element)
140 Wiring 200 Adhesive 210 Adhesive 220 Conductive Material 300 Vibrator

Claims (9)

One end is a fixed end fixed to the substrate, and the other end is a free-ended beam-like vibrator,
A piezoelectric element that vibrates the vibrator;
An element package for applying a voltage to the piezoelectric element;
A vibration detection unit for detecting vibration of the vibrator,
The vibration detection unit includes a pair of detection strain sensors arranged in the width direction of the vibrator in the vicinity of the fixed end of the vibrator;
A pair of reference strain sensors provided on the substrate,
At least one of the detection strain sensors is provided at an end in the width direction of the vibrator,
The vibration detection unit detects at least vibration in a twist mode of the vibrator. On the vibrator, further comprising a sensitive film that adsorbs gas,
2. The detection sensor according to claim 1, wherein vibration characteristics of the vibrator change due to adhesion or adsorption of a substance having mass.   The pair of strain sensors for detection are provided at one end and the other end in the width direction of the vibrator, and the vibration detection unit detects vibration in a torsion mode of the vibrator. The detection sensor according to claim 1 or 2.   The pair of strain sensors for detection are provided at one end in the width direction of the vibrator and at the center in the width direction of the vibrator, and the vibration detection section detects vibration in the bending mode of the vibrator. The detection sensor according to claim 1, wherein the detection sensor is detected. In the vicinity of the base end portion of the vibrator, at least three strain sensors for detection are provided at both ends in the width direction of the vibrator and the intermediate portion in the width direction,
The pair of the detections by the detection strain sensor provided at one end in the width direction of the vibrator and the detection strain sensor provided at the other end in the width direction of the vibrator. Constituting a strain sensor, the vibration detection unit detects torsional mode vibration of the vibrator,
The detection strain sensor provided at one end in the width direction of the vibrator and the detection strain sensor provided in the intermediate portion in the width direction of the vibrator, the pair of detection strain sensors. The detection sensor according to claim 1, wherein the vibration detection unit detects vibration in a bending mode of the vibrator.   The piezoelectric element is bonded to one surface side of the element package, and the substrate having the vibrator is laminated and bonded to the piezoelectric element, and the substrate and the piezoelectric element face four corners of the piezoelectric element or face each other. The detection sensor according to claim 1, wherein the detection sensor is bonded to only two sides using an adhesive.   The sensitive film is any one of polybutadiene (PBD), polyacrylonitrile-butadiene (PAB), polyisoprene (PIP), and polystyrene (PS). The detection sensor described. A substance detection system that detects at least one of the type and concentration of a specific substance contained in a gas to be detected,
A pump for introducing the gas to be detected into the system, and for transporting the introduced gas in the system;
An adsorbing part for adsorbing the specific substance contained in the gas introduced into the system by the pump;
A heater for desorbing the specific substance adsorbed by the adsorption unit from the adsorption unit;
A vibrator whose one end is a fixed end fixed to a substrate and whose other end is a free end, and whose vibration characteristics change due to the attachment or adsorption of a substance having a mass;
A sensitive membrane that adsorbs gas,
A piezoelectric element that vibrates the vibrator;
An element package for applying a voltage to the piezoelectric element;
A vibration detection unit for detecting vibration of the vibrator,
The vibration detection unit includes a pair of detection strain sensors arranged in the width direction of the vibrator in the vicinity of the fixed end of the vibrator;
A pair of reference strain sensors provided on the substrate,
At least one of the detection strain sensors is provided at an end portion in the width direction of the vibrator with respect to the center in the width direction of the vibrator, and the torsion mode vibration and bending mode vibration of the vibrator A substance detection system characterized in that at least torsional mode vibration can be detected. A plurality of the vibrators are provided,
9. The substance detection system according to claim 8, wherein in each of the plurality of sets of vibrators, it is preset whether the detection is performed in one of the torsion mode and the bending mode.

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