JP2011203007A - Detection sensor, and material detection system - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a detection sensor and a material detection system which can achieve high sensitivity, and improving stability and reliability.SOLUTION: The stabilization of vibration characteristics in a vibrator 41 and the improvement of detection sensitivity in a sensitive film 42 are attained by operating a cooling element 152 and by cooling a vibrator chip 100 through a heat conductor 151, a chip package 120 and a PZT plate 130. A heat insulating material 170 covers the surrounding of the heat conductor 151 and the cooling element 152. An electrode part 121 is designed not to contact the outside air by a socket 140, a socket holder 141 and an electrode cover 142. Further, a chamber wall part 145 and a chamber body 146 are formed with a resin such as PEEK (polyether ether ketone) having a lower heat conductivity than a metal.

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 resonance frequency of the vibrator. As vibrators that perform mass detection, there are cantilever vibrators that utilize lateral vibration of a cantilever beam (see, for example, Patent Documents 1 and 2). Such a cantilever type vibrator is manufactured in a micrometer (micrometer) unit area by using a technology called MEMS (Micro Electrical 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.

JP 2007-240252 A JP 2009-133772 A

In such a substance detection system, in order to further increase the detection sensitivity, it is necessary to further reduce the size of the vibrator, and this requires a great deal of cost, including the development of its manufacturing process.
In addition, when moving from the research and development stage to the stage of mass production, it becomes necessary to obtain stable detection sensitivity in many vibrators.
As described above, in the substance detection system, improvement in sensitivity and stability is always required, and the present invention provides a detection sensor and substance detection system that can achieve high sensitivity and stability. For the purpose.

  The detection sensor of the present invention made there is a vibrator, a film-like sensitive film that is formed on the surface of the vibrator and adheres to or adsorbs a substance, a piezoelectric element that vibrates the vibrator, and a voltage applied to the piezoelectric element. An element package for cooling and a cooling member for cooling the vibrator. When the vibrator is cooled by the cooling member, the temperature of the sensitive film formed on the surface of the vibrator decreases. By lowering the temperature of the sensitive membrane, the adsorption rate at the surface of the sensitive membrane and at the adsorption sites in the membrane is greater than the desorption rate, resulting in higher adsorption capacity and greater interaction between adsorbed molecules. Aggregation at the site occurs, resulting in higher adsorption capacity of the entire membrane. That is, the sensitivity of the sensor (frequency change per concentration (Hz / ppm)) is improved.

  Moreover, it is preferable to form a dew condensation prevention part that covers at least one member of the cooling member and the electrode of the element package with a material having a lower thermal conductivity than the material constituting the member.

In addition, the substrate on which the vibrator is formed and the cooling member are stacked, and the substrate is cooled by the cooling member, whereby the vibrator and the sensitive film formed on the vibrator can be cooled.
Further, a piezoelectric element is bonded to one surface side of the element package, a substrate having a vibrator is laminated on the piezoelectric element, and a heat member is taken on the other surface side of the element package to cool the vibrator as a cooling member. A cooling element and a heat transfer member that transmits heat energy taken away by the cooling element from the element package can be stacked.
As described above, by laminating the element package, the piezoelectric element, and the vibrator (with the substrate), vibration generated in the piezoelectric element can be directly transmitted to the vibrator.
In such a configuration, the dew condensation prevention unit can be made of a heat insulating material that covers the surfaces of the cooling element and the heat transfer member.

  Further, a vibration transmission suppressing member that suppresses vibration generated in the piezoelectric element from being transmitted from the element package side to the cooling member can be provided between the element package and the cooling member. Thereby, it is possible to prevent the vibration generated in the piezoelectric element from being disturbed by the cooling member, and to vibrate efficiently.

Further, an electrode to which an external power source is connected can be provided on the outer peripheral portion of the element package, and the electrode can be covered with an electrode cover made of a heat insulating material molded in advance.
Furthermore, the electrode cover is provided on one side and the other side of the element package with respect to the electrode, and the electrode cover is brought into a pressurized state by a pair of housings provided on the one side and the other side of the element package. It can also be a tightened configuration.

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. Pump, an adsorption part that adsorbs a specific substance contained in the gas introduced into the system by the pump, a heater that desorbs the specific substance adsorbed by the adsorption part from the adsorption part, and a specification that is desorbed from the adsorption part An oscillator that has a sensitive film that adsorbs or adheres to a substance, the vibration frequency of which changes when a specific substance is adsorbed or adhered to the sensitive film, a piezoelectric element that vibrates the vibrator, and an element package that applies a voltage to the piezoelectric element And a cooling member that cools the vibrator, and a type of a specific substance obtained by detecting a change in the vibration frequency of the vibrator and based on a change timing of the vibration frequency of the vibrator And and a detection unit for detecting at least one of the concentration of a specific substance obtained based on the variation of the vibration frequency. And at least 1 member of the cooling member and the electrode of an element package is covered with the material whose heat conductivity is smaller than the material which comprises the said member.
Here, the vibrator is provided in a chamber into which the specific substance desorbed from the adsorption portion is sent by a pump, and the chamber can be formed of a resin-based material. By forming the chamber with a resin-based material, it is possible to make it difficult to condense as compared with the case where the chamber is made of metal.

  According to the present invention, it is possible to increase the detection sensitivity and improve the stability by cooling the vibrator coated with the sensitive film.

It is a figure which shows schematic structure of the substance detection system in this Embodiment. It is sectional drawing which shows an adsorption | suction part. It is a perspective view which shows the laminated structure of the vibrator | oscillator which comprises a sensor part, a PZT board, and a chip package. It is sectional drawing which shows the cooling structure of a sensor part. It is a figure which shows the difference in the frequency change by the presence or absence of cooling. It is a figure which shows the temperature characteristic by the material which forms a sensitive film | membrane. It is a figure which shows the cooling element temperature at the time of not employ | adopting a dew condensation prevention structure, and the frequency change of a vibrator | oscillator. It is a figure which shows the cooling capacity by a cooling element. It is a figure which shows the difference in the output signal of a vibrator | oscillator by the presence or absence of a vibration transmission member.

Hereinafter, the present invention will be described in detail based on embodiments shown in the accompanying drawings.
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 and generates a gas flow in the system, an adsorption unit 30 that adsorbs the gas sucked in the pump 20, and the gas adsorbed by the adsorption unit 30. The sensor unit (detection sensor) 40 that adsorbs a specific type of molecule contained in the gas component and outputs a detection signal corresponding to the adsorption of the molecule, and the specific type of molecule based on the detection signal in the sensor unit 40 And a measurement processing unit (detection unit) 50 that measures the presence or absence or the amount thereof.

  The pump 20 is, for example, electric, and the suction / discharge amount can be adjusted by controlling the applied voltage / current. Ambient atmosphere gas or gas in the sample container 15 connected to the suction nozzle is sucked from a suction nozzle (not shown) and discharged from the discharge port. The suction nozzle of the pump 20 is preferably provided with an open / close valve or the like so as to block the suction of gas into the pump 20.

The adsorption unit 30 is connected to the discharge port of the pump 20 by a gas transport pipe 60.
As shown in FIG. 2, 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. Here, if the tube diameter of the cylinder 31 is too small, the flow resistance of the gas increases, and even if the tube diameter is too large, a time difference occurs in the diffusion of gas in the cylinder 31 and leads to a decrease in gas separation performance. Further, in order to increase the detection accuracy, an optimum gas flow rate determined by the volume of the cylinder 31 and the chamber volume of the sensor unit 40 is adopted, and the specific surface area of the carbon fiber as the adsorbent is increased, so that per unit time. It is preferable to increase the amount of adsorbed molecules.
In the adsorption unit 30, the pump 20 is operated for a predetermined time, and the molecules in the gas fed during the operation are adsorbed by the adsorbent. The sampling amount of the gas can be determined by the operation time of the pump 20, that is, the length of the adsorption time in the adsorption unit 30. In addition, the pump 20 may be provided on the downstream side of the adsorption unit 30 or the sensor unit 40 and suck gas. Here, the sample container 15 can be a sample bag made of thin plastic. In this case, since the gas sample can be introduced into the adsorption unit 30 by applying pressure to the sample bag, the pump 20 can be omitted.

A sheath heater 34 is wound around the outer peripheral surface of the cylindrical body 31. The sheath heater 34 is fixed to the cylindrical body 31 by a heat conductive cement (not shown), and the outer peripheral side thereof is thermally insulated by a heat insulating material 33 and further accommodated in a case 36 through an air layer. A thermometer 35 is provided in the vicinity of the sheath heater 34.
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 sensor unit 40 by the flow generated by the pump 20.

As shown in FIG. 1, the sensor unit 40 is connected to the adsorption unit 30 by a gas transport pipe 60. The sensor unit 40 includes a vibrator 41 that generates mechanical vibrations, and a sensitive film 42 that is formed on the surface of the vibrator 41 and adsorbs the molecules desorbed by the adsorption unit 30.
As shown in FIG. 3, the vibrator 41 is a cantilever type having a width of 20 to 400 μm, a length of 100 to 1000 μm, a base end portion fixed, and the other end portion being a free end. The vibrator 41 uses, for example, a piezo drive system as a drive source, and vibrates the vibrator 41 at a predetermined frequency. 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 using, for example, a piezoelectric effect of silicon or a piezoelectric element.

The sensitive film 42 can be formed of an organic material or an inorganic material. In the present embodiment, polybutadiene (PBD), polyacrylonitrile-butadiene (PAB), polyisoprene (PIP), polystyrene (PS), or the like can be used as the sensitive film 42. 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. PAB has selectivity for VOCs such as octane and propanol. PBD and PIP have selectivity for toluene, and PS has high selectivity for npropanol and ethanol. PS has a slow response time. Based on these differences in selectivity, a combination of a plurality of types of sensitive membranes can improve the substance selection accuracy.
The sensitive film 42 may be formed on the surface of the vibrator 41 by an appropriate method such as a dropping method or a spin coating method.

  Here, as shown in FIG. 1, the vibrator 41 on which the sensitive film 42 is formed is provided in a chamber 43 having a predetermined volume (for example, 0.1 to 0.5 cc). In the chamber 43, a plurality of vibrators 41 each having the sensitive film 42 as described above are installed.

The measurement processing unit 50 includes a drive circuit 51 for driving the vibrator 41 and a detection circuit 52 for detecting an electrical signal from the vibration detection unit 44.
Under the control of the measurement processing unit 50, the transducer 41 of the sensor unit 40 is driven by an electric signal from the drive circuit 51 and vibrates at a predetermined frequency, and a detection object such as a molecule having a mass in the sensitive film 42. 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 the substance detection system 10 shown in FIG. 1, operation of the pump 20, heating by energizing the sheath heater 34, driving and detection of the vibrator 41, and measurement processing in the measurement processing unit 50 are controlled by a control unit (not shown).
That is, first, gas is sucked by the pump 20 for a predetermined time, and molecules contained in the gas are adsorbed by the adsorption unit 30. After the elapse of the predetermined time, the suction of gas from the pump 20 is stopped while the pump 20 is operated.
Next, air or an inert gas prepared separately is flowed from the pump 20 at a preset flow rate, and the sheath heater 34 is energized to heat the adsorption unit 30 and separate the component molecules adsorbed by the adsorption unit 30. Then, the separated component molecules are transported to the sensor unit 40 by the gas transport pipe 60 and are adsorbed by the sensitive film 42 of the vibrator 41. As a result, the vibration frequency of the vibrator 41 changes. In the measurement processing unit 50, a change in vibration frequency of the vibrator 41 is detected. In the measurement processing unit 50, in each of the vibrators 41 including the sensitive film 42, data such as a vibration frequency change amount, a change response timing, and the like, which are measured in advance according to the type and amount (concentration) of the component molecule. It is remembered. The measurement processing unit 50 measures (specifies) the type and amount (concentration) of the component molecules adsorbed on the sensitive film 42 by comparing the detected vibration frequency change of the vibrator 41 with previously stored data. To do.

Here, in the chamber 43, a plurality of sets of vibrators 41 each having the sensitive film 42 as described above are installed.
Now, among the plural sets of vibrators 41, for example, the type of the sensitive film 42 can be made different from each other. Using a plurality of types of sensitive films 42 having different sensitivities to component molecules (adsorption / capture levels of component molecules), the vibration change of the vibrator 41 provided with the sensitive films 42 is processed by the measurement processing unit 50, thereby capturing. It is possible to specify the type of component molecules. In this way, the analysis / identification function can be improved for various types of component molecules.

In this way, the substance contained in the gas can be identified and its concentration can be measured. At this time, the discriminating ability is enhanced by making the material of the sensitive film 42 different. Further, by detecting the desorption timing when the substance is desorbed from the adsorbent by the heating of the sheath heater 34 with the sensor unit 40 and the measurement processing unit 50, the ability to identify the type of the substance is enhanced.
In addition, by compressing and feeding the gas in the pump 20, it becomes possible to perform highly sensitive detection even with a small amount of gas, and the substance detection system 10 should be equipped with highly sensitive detection performance that is unprecedented in spite of its small size. Can do. Such a substance detection system 10 can be easily manufactured except for the vibrator 41 manufactured by a microfabrication technique such as a MEMS (Micro Electro Mechanical Systems) technique, thereby reducing the cost. Become.

Now, a driving structure of the vibrator 41 of the sensor unit 40 in the substance detection system 10 as described above will be described.
As shown in FIG. 3, 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 an unnecessary portion by etching or the like. The vibrator 41 is a fixed end in which one end 41a is fixed to the substrate body 101, and the other end. 41b is an overhanging free end. A vibration detector 44 is disposed on one end 41a of the vibrator 41, and the vibration detector 44 detects the vibration displacement of the vibrator 41 as an electric signal.

  As shown in FIG. 4, such a transducer chip 100 is supported on a base substrate 110 serving as a base of the sensor unit 40 via a chip package (element package) 120 and a PZT plate (piezoelectric element) 130. ing.

  An opening 111 is formed in the base substrate 110. 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 so as to close the opening 111. 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 125 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.

  As shown in FIG. 3, 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.

  As shown in FIG. 4, the sensor unit 40 includes a cooling mechanism (cooling member) 150. The cooling mechanism 150 cools the transducer chip 100 on which the transducer 41 is formed. When the vibrator 41 having the sensitive film 42 is cooled, the sensor sensitivity by gas adsorption is improved. This is because the sensitivity is improved when the sensitive film 42 is cooled. Therefore, it is preferable to control the temperature of the vibrator 41 and the sensitive film 42 by the cooling mechanism 150 to a constant temperature within the range of -20 to 20 ° C, more preferably -5 to 10 ° C.

The cooling mechanism 150 may have any configuration as long as it can satisfy such a purpose. For example, the following configuration can be adopted.
That is, the cooling mechanism 150 is disposed on the other surface side of the base substrate 110 and is provided on the other surface side of the chip package 120 exposed to the opening 111 via the heat conductor (heat transfer member) 151. The cooling element 152 and the heat sink 153. The heat sink 153 can be provided with a heat radiating fin or a heat radiating fan in order to further improve the heat radiating property.

The heat conductor 151 is in the form of a block made of, for example, Cu and is deprived of heat from the chip package 120 by being cooled by the cooling element 152. Here, the heat conductor 151 is joined to the other surface side of the chip package 120 by a conductive material 154 made of a material having high heat conductivity and low conductivity (for example, a silicone paste containing a metal oxide). preferable.
Any element may be used as the cooling element 152, but a Peltier element is preferably used from the viewpoint of responsiveness.

  In such a cooling mechanism 150, the cooling element 152 is operated based on the appropriate position of the sensor unit 40 detected by the sensor 155 (in this embodiment, the heat conductor 151), and the heat conductor 151 and the chip are operated. -The vibrator 41 and the sensitive film 42 are cooled by cooling the vibrator chip 100 via the package 120 and the PZT plate 130. Thereby, the detection sensitivity in the vibrator 41 and the sensitive film 42 can be improved, and the substance detection sensitivity in the substance detection system 10 can be improved.

By the way, if the transducer chip 100 is continuously cooled by the cooling mechanism 150 for a long time, condensation may occur on the heat conductor 151, the electrode of the chip package 120, and the like. Then, moisture adheres to these surfaces, the heat capacity thereof changes, and the temperature becomes unstable.
Further, the dew condensation on the electrodes of the chip package 120 causes an electrical impedance change of the PZT plate 130 and the vibration detection unit 44, and the oscillation frequency of the vibration may fluctuate or the oscillation may stop.

In order to protect the electric circuit from condensation generated by cooling, for example, a circuit board is housed in a case, and a part that generates condensation is provided in the case above the circuit to prevent the circuit from being exposed to condensation. A technique has been proposed (see, for example, Japanese Patent Application Laid-Open No. 2001-346312).
However, with such technology, it is possible to prevent the circuit in other parts of the case from being exposed to condensation by providing a part that generates condensation, but it is possible to reliably prevent the circuit from condensation. There wasn't. Further, with such a structure, there is a problem that the case becomes complicated and the cost of the case is increased.

Therefore, the present inventors have studied for the purpose of reliably preventing condensation while having a simple configuration, and as a result, have found that the following configuration is effective for realizing the purpose.
The configuration will be described below.

Between the heat conductor 151 and the chip package 120, an elastic body (vibration transmission suppressing member) 156 such as PDMS (Poly dimethyl siloxane), polymer fiber, and cotton is sandwiched. The elastic body 156 has a rectangular ring shape with an opening 156a formed at the center, and the conductive material 154 is filled in the opening 156a.
The elastic body 156 can prevent vibration generated in the PZT plate 130 from being transmitted from the chip package 120 to the thermal conductor 151 and inhibiting the vibration. Thereby, it is possible to prevent the electrical signal of the vibration displacement of the vibrator 41 detected by the vibration detection unit 44 from deteriorating and the oscillation of vibration in the PZT plate 130 from becoming unstable.

  In the present embodiment, in the above configuration, the heat conductor 151 and the cooling element 152 are covered with a heat insulating material (condensation prevention unit) 170 made of a material having a smaller thermal conductivity than these. The heat insulating material 170 may be any plastic material that can be easily processed, but PEEK (polyether ether ketone) or the like can be used. Thereby, it is possible to prevent the heat conductor 151 and the cooling element 152 from dewing, and it is possible to prevent the chip package 120 from getting wet.

Further, the electrode part 121 of the chip package 120 and the extraction electrode 122 electrically connected to the electrode part 121 are fixed to the socket (housing) 140 attached to the substrate 110 constituting the fixing member 112 and the socket 140. Is sandwiched between a socket holder (housing) 141 and an electrode cover (condensation prevention unit) 142.
The side of the socket 140 facing the substrate 110 of the electrode part 121 of the chip package 120 abuts. Further, the socket 140 is formed with an insertion hole 140a through which the wiring portion 122a of the extraction electrode 122 connected to the electrode portion 121 is inserted. The wiring part 122 a is led out to the substrate 110 side through the insertion hole 140 a and is electrically connected to the wiring pattern of the substrate 110.
The socket retainer 141 is formed so that the fixing portion 141 a surrounds the chip package 120, and is connected to the socket 140 by a bolt or the like on the outer peripheral side of the electrode portion 121. The socket restraint 141 further includes a restraining plate portion 141b that protrudes inward from the fixed portion 141a. The plate portion 141b is formed to face the electrode portion 121 with a space therebetween.

  In addition, a chamber wall 145 is formed in the chip package 120 so as to surround the outer peripheral side of the PZT plate 130 and the transducer chip 100.

  The electrode cover 142 is formed in a predetermined shape in advance, and is provided in the gap between the chamber wall 145, the socket 140, and the socket holder 141. The socket 140 and the socket retainer 141 are fastened to each other by a bolt or the like, and the electrode cover 142 sandwiched therebetween is fastened in a pressurized state. As a result, the electrode part 121 protruding outward from the chamber wall part 145 is sandwiched between the socket 140 and the socket holder 141 in a pressurized state so as not to touch the external atmosphere. Thereby, it can prevent that the electrode part 121 dews and gets wet. As the electrode cover 142, it is preferable to use one having a thermal conductivity smaller than that of the electrode portion 121 and having heat insulation, insulation, vibration absorption, and heat insulation. Specifically, PDMS (Polydimethylsiloxane) or the like can be used as the electrode cover 142.

A chamber body 146 is provided on the chamber wall 145 with a sealant 147 interposed therebetween. Thus, the transducer chip 100 is located in the closed space S surrounded by the chip package 120, the chamber wall 145, and the chamber body 146.
The chamber body 146 has an introduction port 146a and a discharge port 146b. From the introduction port 146a, gas is fed into the closed space S from the gas transport pipe 60, and from the discharge port 146b to the inside of the closed space S. Gas is discharged to the outside.

  Here, the chamber wall 145 and the chamber body 146 are formed of a resin having a lower thermal conductivity than that of metal, such as PEEK (polyether ether ketone). Thereby, it can prevent that the chamber wall part 145 and the chamber main body 146 get wet by dew condensation.

  In this way, it is possible to prevent the heat conductor 151 from getting wet due to dew condensation, so that moisture adhering to these surfaces prevents the heat capacity from changing and the temperature from becoming unstable. it can. In addition, by preventing dew condensation on the chip package 120 and the electrode part 121, changes in the electrical impedance of the PZT plate 130 and the vibration detection part 44 are prevented, and the oscillation frequency of the vibration fluctuates or oscillation stops. Can be prevented.

In this manner, detection sensitivity can be stably increased by cooling the vibrator 41 and the sensitive film 42 by the cooling element 152 and preventing condensation due to cooling.
And the structure for preventing dew condensation is very simple, and the said effect can be acquired easily at low cost. Thereby, detection sensitivity can be raised.

  Further, according to the above configuration, since the vibrator chip 100 is directly bonded to the PZT plate 130, vibration generated in the PZT plate 130 can be efficiently transmitted to the vibrator chip 100.

Here, since the configuration shown above was verified, the results are shown below.
(Verification of the effect of cooling)
As the vibrator 41 of the sensor unit 40, a cantilever type was prepared.
The cantilever-type vibrator 41 was produced from an SOI (Silicon on Insulator) substrate using a MEMS process. First, an oxide layer is formed on a 5 μm-thick active layer of an N-type SOI substrate, a pattern is formed by photolithography, and boron P-type diffusion is performed to form a Si piezoresistive layer as a detection circuit. After that, a vibrator 41 having a length of 500 μm and a width of 100 μm was formed by RIE (Reactive Ion Etching) etching method. Thereafter, in order to reduce attenuation due to air damping, the silicon of the support layer was removed from the back surface by a Deep-RIE etching method.
One or two Si piezoresistors (about 2K ohms) as a detection circuit are arranged at the base of the vibrator 41, and a Wheatstone bridge is formed together with other reference piezoresistors. Further, a gold film of about 100 nm was formed on the surface of the vibrator 41 through a silicon oxide film and an adhesive layer Cr.

A PAB film having a film thickness of 1.1 μm having excellent adsorption characteristics to acetone or toluene was formed as a sensitive film 42 on the upper surface of the cantilever type vibrator 41 by using a dispenser and then dried.
Then, the cooling effect of the vibrator 41 and the sensitive film 42 was evaluated.
Here, the configuration of the present embodiment shown in FIG. 3 is used, and the cooling mechanism 150 is operated to set the chamber 43 provided with the vibrator 41 to 8 ° C., and the cooling mechanism 150 is not operated and the vibration is In the case where the chamber 43 in which the element 41 is provided is set to 28 ° C., the adsorption response characteristic with respect to a diluted mixed gas of 200 CC acetone 3000 ppm and toluene 1000 ppm was measured. Specifically, first, after the inside of the chamber 43 in which the vibrator 41 was installed was made a nitrogen atmosphere, the gas to be measured was introduced. The gas was introduced for several minutes and the frequency change was measured. Thereafter, the gas in the chamber was evacuated and replaced with nitrogen to return the frequency to the baseline.
The result is shown in FIG. Here, FIG. 5A shows frequency changes when the chamber 43 is set to 28 ° C., and FIG. 5B shows frequency changes when the chamber 43 is set to 8 ° C.
As a result, by cooling the vibrator 41 by the cooling mechanism 150, the vibration characteristics of the vibrator 41 are significantly improved, and 1.6 Hz / ppmL (no cooling) → 7.5 Hz / ppmL (with cooling) with acetone, It was confirmed that the detection sensitivity was significantly increased with toluene at 7.5 Hz / ppmL (no cooling) → 41.3 Hz / ppmL (with cooling). Here, the unit Hz / ppm is sensitivity Hz / ppm per liter of sample volume.

Next, in the same configuration as described above, when the sensitive film 42 is made of PBD (film thickness 1.7 μm), the cooling mechanism 150 is similarly operated for 200 CC ethanol 1000 ppm and toluene 1000 ppm lean mixed gas. Measurement of adsorption response characteristics when the chamber 43 provided with the vibrator 41 is set to 8.3 ° C. and when the chamber 43 provided with the vibrator 41 is set to 28 ° C. without operating the cooling mechanism 150. did.
As a result, 1.6 Hz / ppmL (without cooling) for ethanol → 6.5 Hz / ppmL (with cooling), 12.5 Hz / ppmL (without cooling) with toluene → 48.0 Hz / ppmL (with cooling), cooling mechanism It was confirmed that the detection sensitivity is greatly increased by cooling the vibrator 41 with 150.

Next, in order to investigate the characteristics of the sensitive film 42, first, a frequency change was measured when 2000 ppm of toluene was introduced using a QCM (Quarts Crystal Microbalance). Specifically, first, the inside of the chamber where the QCM was installed was put into a nitrogen atmosphere, and then the gas to be measured was introduced. The gas was introduced for several minutes and the frequency change was measured. Thereafter, the gas in the chamber 43 was evacuated and replaced with nitrogen to return the frequency to the baseline. The frequency change was measured by changing the temperature in the chamber 43 to 10 to 58 ° C. The sensitive film 42 applied on the QCM was PAB, and the film thickness was 180, 200, and 430 nm.
FIG. 6 shows the result of obtaining the K factor from the result using the film thickness of the sensitive film 42 and the gas concentration. The K factor is a solubility parameter (index) indicating how much a gas or molecule in the air dissolves in an adsorbent material such as a polymer, and can be calculated by the equation (1). Here, M _cv is the weight concentration (g / cm ³ ) of the chamber 43 in the sensitive film 42, f _g is the frequency at the time of gas adsorption, f _f is the frequency at which the sensitive film 42 is formed, and f ₀ is the film formed. The frequency of the previous crystal, ρ _f, is the density of the sensitive film 42.
The K factor varies depending on the combination of the sensitive film 42 and the type of adsorbed molecule, and the larger the K factor value, the better the sensitivity of the sensitive film 42.

  As shown in FIG. 6, the K factor increases as the temperature decreases. For example, the K factor increases approximately three times at a low temperature of 10 ° C. as compared to 30 ° C. It is confirmed that the detection sensitivity is improved by lowering the temperature of the sensitive film 42.

(Verification of condensation prevention measures)
First, in the configuration in which the elastic body 156, the heat insulating material 170, and the electrode cover 142 are omitted from the configuration illustrated in FIG. 4, a voltage is applied to the Peltier element as the cooling element 152. The temperature of the cooling element 152 at that time and the amount of change in the frequency of the vibrator 41 were measured, and the cooling element 152, the electrode part 121 of the chip package 120, and the extraction electrode 122 were visually observed.
The result is shown in FIG.

  As shown in FIG. 7, when a voltage is applied to the cooling element 152, the temperature of the cooling element 152 decreases and the vibrator 141 starts to vibrate. However, after about 15 minutes, the temperature of the cooling element 152 dropped rapidly, and stable oscillation of the vibrator 41 stopped. When visually observed, condensation occurred on the cooling element 152, the electrode portion 121 of the chip package 120, and the extraction electrode 122.

On the other hand, in the configuration shown in FIG. 4, when a voltage is applied to a Peltier element as the cooling element 152 every 1.8 seconds up to 1.8 V in steps of 0.3 V, the room temperature, the heat conductor 151, the chip The temperature change of the package 120 is shown.
As shown in FIG. 8, by applying a voltage, the heat conductor 151 and the chip package 120 were cooled from around room temperature to around 7 ° C.
Further, the above voltage application was repeated for 3 hours, but the temperature change did not become unstable.

(Verification of vibration transmission suppression member)
Next, in the configuration shown in FIG. 4, there are a case where an elastic body 156 made of PDMS is sandwiched between the heat conductor 151 and the chip package 120 and a case where the elastic body 156 is omitted. The difference of 41 output signals was verified. Except for the presence or absence of the elastic body 156, the conditions are the same as in the first embodiment.
The result is shown in FIG.
As shown in FIG. 9A, the level of the output signal is clearly higher when the elastic body 156 is sandwiched as shown in FIG. 9B than when the elastic body 156 is not sandwiched. Was confirmed.

In the above-described embodiment, the substance detection system 10 has been described. However, the configuration other than the cooling mechanism 150 of the sensor unit 40 may be appropriately configured.
For example, although the cantilever type is used as the vibrator 41, it is not limited to this. In addition, a disk type may be used as the vibrator 41, and the present invention can also be applied when a so-called QCM is used as the sensor unit 40.
In addition to this, as long as it does not depart from the gist of the present invention, the configuration described in the above embodiment can be selected or changed to another configuration as appropriate.

  DESCRIPTION OF SYMBOLS 10 ... Substance detection system, 20 ... Pump, 30 ... Adsorption part, 40 ... Sensor part, 41 ... Vibrator, 42 ... Sensitive membrane, 43 ... Chamber, 44 ... Vibration detection part, 50 ... Measurement processing part (detection part), DESCRIPTION OF SYMBOLS 100 ... Vibrator chip | tip, 110 ... Base substrate, 120 ... Chip package (element package), 121 ... Electrode part, 130 ... PZT board (piezoelectric element), 140 ... Socket (housing), 141 ... Socket restraint (housing), 142 ... Electrode cover (condensation prevention part), 145 ... chamber wall part, 146 ... chamber main body, 150 ... cooling mechanism (cooling member), 151 ... heat conductor (heat transfer member), 152 ... cooling element, 153 ... heat sink, 154 ... Conductive material, 156 ... Elastic body (vibration transmission suppressing member), 170 ... Heat insulating material (condensation prevention part)

Claims (10)

A vibrator,
A film-like sensitive film formed on the surface of the vibrator and adhering or adsorbing a substance;
A piezoelectric element that vibrates the vibrator;
An element package for applying a voltage to the piezoelectric element;
And a cooling member for cooling the vibrator.   2. A dew condensation prevention part is formed, wherein at least one member of the cooling member and the electrode of the element package is covered with a material having a lower thermal conductivity than a material constituting the member. The detection sensor described in 1. The substrate on which the vibrator is formed and the cooling member are laminated,
The detection sensor according to claim 1, wherein the substrate and the sensitive film formed on the vibrator are cooled by cooling the substrate with the cooling member. The piezoelectric element is bonded to one surface side of the element package, and the substrate is laminated on the piezoelectric element,
On the other surface side of the element package, as the cooling member, a cooling element that takes heat energy to cool the vibrator, and a heat transfer member that transfers heat energy taken by the cooling element from the element package are stacked. The detection sensor according to claim 3, wherein the detection sensor is provided.   The detection sensor according to claim 4, wherein the dew condensation prevention unit is made of a heat insulating material that covers surfaces of the cooling element and the heat transfer member.   The vibration transmission suppressing member for suppressing vibration generated in the piezoelectric element from being transmitted from the element package side to the cooling member is provided between the element package and the cooling member. The detection sensor according to any one of 1 to 5. An electrode to which an external power source is connected is provided on the outer periphery of the element package,
The detection sensor according to any one of claims 1 to 6, wherein the electrode is covered with an electrode cover made of a heat insulating material molded in advance. The electrode cover is provided on one side and the other side of the element package with respect to the electrode,
The detection sensor according to claim 7, wherein the electrode cover is clamped in a pressurized state by a pair of housings provided on one side and the other side of the element package. 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 sensitive film that adsorbs or adheres the specific substance desorbed from the adsorbing portion, and a vibrator whose vibration frequency changes by adsorbing or adhering the specific substance to the sensitive film;
A piezoelectric element that vibrates the vibrator;
An element package for applying a voltage to the piezoelectric element;
A cooling member for cooling the vibrator;
The change in the vibration frequency of the vibrator is detected, the type of the specific substance obtained based on the change timing of the vibration frequency of the vibrator, and the concentration of the specific substance obtained based on the amount of change in the vibration frequency. A detection unit for detecting at least one of
The substance detection system, wherein at least one member of the cooling member and the electrode of the element package is covered with a material having a lower thermal conductivity than a material constituting the member. The vibrator is provided in a chamber into which the specific substance desorbed from the adsorption unit is sent by the pump,
The substance detection system according to claim 9, wherein the chamber is made of a resin material.

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