KR100865040B1 - Integrated surface acoustic wave based micro-sensor - Google Patents

Abstract

An integrated SAW(Surface Acoustic Wave) based micro-sensor is provided to measure an RFID(Radio Frequency IDentification) tag signal, temperature, and pressure by including an RFID tag, a temperature sensor, and a pressure sensor, and using received RF energy. An antenna(115) transceives a pulse signal on a lower substrate(110). A first IDT(Inter Digital Transducer)(120) converts the pulse signal received through the antenna into an SAW signal and outputs the SAW signal on the lower substrate. An RFID tag reflector(125) is mounted on the lower substrate and includes reflectors capable of measuring an RFID signal by reflecting the SAW signal. A temperature sensor reflector(130) is mounted on the lower substrate and includes the reflectors capable of measuring temperature by reflecting the SAW signal. A pair of metal rods(145) are connected to the first IDT on the lower substrate. A second IDT(155) converts the pulse signal received from the antenna through the metal rods into the SAW signal and outputs the SAW signal on an upper substrate(150). A pressure sensor reflector(160) is mounted on the upper substrate and includes the reflectors capable of measuring pressure by reflecting the SAW signal.

Description

Integrated surface acoustic wave based micro-sensor

1 is a perspective view of an integrated surface acoustic wave-based microsensor according to the present invention.

FIG. 2 is a plan view of the integrated surface acoustic wave based microsensor of FIG. 1. FIG.

3 is an electrical connection diagram between an upper substrate and a lower substrate.

4 is a view illustrating a process of bonding an upper substrate and a lower substrate.

5 is a view showing a connection between the integrated surface acoustic wave-based microsensor and the network analyzer according to the present invention.

6 is a graph of reflection peak over time as seen through a network analyzer.

The present invention relates to a microsensor, and more particularly to an integrated surface acoustic wave-based microsensor having not only an RFID tag and a temperature sensor but also a pressure sensor.

Recently, surface acoustic wave (SAW) -based microsensors have been widely used in tire pressure monitoring systems, temperature sensors, biosensors and environmental gas sensors. Surface acoustic wave-based microsensors have the following advantages over conventional sensors:

First, a battery is needed to operate the sensor by generating surface acoustic waves on the surface of the microsensor using RF energy supplied from the outside and measuring the time, phase, and amplitude change of the surface acoustic waves reflected back by the reflector. none.

Second, since there is no need to embed semiconductor IC chips, it can maintain stable characteristics for a long time even in harsh and harsh environments (high temperature, humidity, shock, etc.). Third, dozens of meters of long-range wireless communication is possible, even with small RF energy supplied from the outside. Fourth, it is possible to detect the real-time sensing factor in the fast rotating and moving area as in a car tire.

However, conventional surface acoustic wave-based microsensors have a problem of inferior measurement accuracy due to large signal attenuation, broad reflection peaks, and signal evaluation errors. In addition, conventional surface acoustic wave-based microsensors for measuring temperature or pressure only have a single sensor for measuring each independent component, but integrated surface acoustic wave-based microsensors that can measure various components are not reported. It is not.

The technical problem to be achieved by the present invention is to provide an integrated surface acoustic wave-based microsensor that can measure the pressure as well as the RFID tag signal and temperature using the RF energy supplied wirelessly.

Integrated surface acoustic wave-based microsensor according to the present invention for achieving the above technical problem, the lower substrate; An antenna formed on the lower substrate to wirelessly transmit and receive a pulse signal; A first inter digital transducer (IDT) for converting a pulse signal received from the antenna into surface acoustic waves and outputting the first signal; An RFID tag reflector unit spaced apart from the first IDT by a predetermined distance and mounted on the lower substrate and having a plurality of reflectors capable of reflecting the surface acoustic wave to measure radio frequency identification (RFID) information; And a reflector for a temperature sensor spaced apart from the first IDT by a predetermined distance and mounted on the lower substrate and having a plurality of reflectors capable of reflecting the surface acoustic wave to measure temperature.

The integrated surface acoustic wave-based microsensor includes a pair of metal bars connected to the first IDT and formed on the lower substrate; An upper substrate installed on the metal bar; A second IDT formed on the upper substrate to convert a pulse signal received from the antenna through the metal rod into a surface acoustic wave; A reflector unit for a pressure sensor spaced apart from the second IDT and mounted on the upper substrate and having a plurality of reflectors capable of reflecting the surface acoustic wave to measure pressure; And a support configured to support the upper substrate and surround the metal bar while sealing four surfaces between the upper substrate and the lower substrate.

The lower substrate and the upper substrate is preferably made of a piezoelectric material.

The piezoelectric material is preferably any one of LiNbO ₃ , LiTaO _3, and quartz.

The antenna is preferably formed to coil around the first IDT and the reflector in a coil form in order to maximize the antenna length while minimizing the area occupied on the lower substrate.

The antenna preferably has a frequency band in which the intermediate frequency is 2.4 GHz.

The RFID tag reflector, the RFID tag reflector,

It is desirable to have any number of reflector groups consisting of any number of reflectors and to read the RFID for each of the groups to maximize the number of cases of RFID.

The first IDT and the second IDT preferably have a single phase unidirectional transducer (SPUDT) structure.

It is preferable that the reflector portion for the RFID tag and the reflector portion for the temperature sensor use two radio tracks.

In order to fully understand the present invention, the operational advantages of the present invention, and the objects achieved by the practice of the present invention, reference should be made to the accompanying drawings which illustrate preferred embodiments of the present invention and the contents described in the accompanying drawings.

Hereinafter, exemplary embodiments of the present invention will be described in detail with reference to the accompanying drawings. For each figure, like reference numerals denote like elements.

1 is a perspective view of an integrated surface acoustic wave based microsensor according to the present invention, FIG. 2 is a plan view of an integrated surface acoustic wave based microsensor according to the present invention, and FIG. 3 is an electrical diagram between an upper substrate and a lower substrate. The connection diagram is shown.

1 to 3, the integrated surface acoustic wave-based microsensor 100 includes a lower substrate 110, an antenna 115, a first inter digital transducer (IDT) 120, and a reflector 125 for an RFID tag. And a reflector 130 for the temperature sensor.

The lower substrate 110 is made of a material having piezoelectricity. For example, LiNbO ₃ , LiTaO ₃ , quartz, or the like may be used. In particular, 41 ^o YX LiNbO ₃ piezoelectric substrates are preferred because they have a high surface acoustic wave propagation rate and a large electrochemical coupling factor. High surface acoustic wave propagation speeds facilitate the patterning of devices in manufacturing. Large electrochemical coupling factors also result in high reflectivity from the reflectors and low insertion loss.

The antenna 115 is formed on the lower substrate 110 to transmit and receive a pulse signal wirelessly. The antenna 115 is for communication in the frequency band of the intermediate frequency of 2.4 GHz, and is formed to coil around the reflector unit 125 and the temperature sensor reflector 130 for the RFID tag in a high-gain plane integrated manner. Thus, the antenna length is maximized while minimizing the area occupied on the lower substrate 110.

The antenna 115 is formed by selectively depositing SiO ₂ on the lower substrate 110 of 41 ^o YX LiNbO ₃ by about 500 nm, and then depositing and patterning copper (Cu).

The first IDT 120 generates a surface acoustic wave (SAW) by applying an electrical signal or an RF signal to a plurality of metal electrodes formed in parallel with each other. In addition, the first IDT 120 converts the surface acoustic wave reflected from the reflector 125 for the RFID tag and the reflector 130 for the temperature sensor into an RF signal and outputs the RF signal to the antenna 115.

In addition, since the first IDT 120 has a single phase unidirectional transducer (SPUDT) structure, the surface acoustic wave is propagated in one direction without propagating in both directions about the IDT 120. Minimize power loss of RF energy.

The reflector 125 for the RFID tag is mounted on the lower substrate 110 spaced apart from the first IDT 120 by a predetermined distance, and reflects the surface acoustic wave to measure the RFID information. 125h) (see FIG. 3). Although FIG. 3 shows eight reflectors, the present invention is not limited thereto and may include various numbers of reflectors.

Each of the reflectors 125a, ..., 125h of the reflector 125 for an RFID tag is made of aluminum.

The next-generation bar code specification, Electronic Product Code (EPC), requires dozens of barcode-type reflectors. When these reflectors are arranged in a line, the reflection peaks obtained from the reflectors located far from the IDT may cause severe signal attenuation and error peaks due to multiple reflections, thereby limiting the number of reflectors in the form of barcodes.

In order to solve this problem, the present invention does not read the entire reflector as a single RFID tag, but includes one or more reflector groups composed of one or more reflectors, which can be leaked by reading RFID for each of the groups. Maximize the number of cases. For example, if two reflectors are set to one group out of eight RFID reflectors, each RFID can be read from four groups, and if four reflectors are set to one group, two groups are used. Each RFID can be read from. In addition, the number of reflectors may be set differently for each group. For example, five reflectors may be set in the first group and three reflectors may be set in the second group to read RFID in each of the first group and the second group.

Also, the reflection peaks from the RFID reflectors appear to overlap each other. This is a result of installing a plurality of reflectors in a limited area. However, since the center points of the peaks do not overlap, only a peak having an amplitude value greater than or equal to a predetermined threshold value is read as the reflector peak, whereby a large number of reflectors can be inserted in the limited area, thereby increasing the number of RFID cases.

The reflector 130 for the temperature sensor is mounted on the lower substrate 110 by being spaced apart from the first IDT 120 by a predetermined distance, and includes a plurality of reflectors 130a capable of measuring temperature by reflecting surface acoustic waves. 130b, 130c (see FIG. 3).

As the temperature changes, the propagation distance and velocity of the SAW change, causing a change in the position of the reflection peak. The difference between the reflection peak measured at the current temperature and the reflection peak at the reference temperature varies linearly with the degree of displacement of the temperature. This difference can be used to measure temperature.

In addition, the amount of change of the peak with the chart is charted, and the maximum temperature measurement range can be calculated by measuring the linear and nonlinear change regions.

In the exemplary embodiment of the present invention, the reflector 130 for the temperature sensor is illustrated as having three reflectors 130a, 130b, and 130c in FIG. 3, but is not limited thereto, and may include various numbers of reflectors. have.

The reflectors used for the reflector portion 125 for the RFID tag and the reflector portion 130 for the temperature sensor use a short-circuit type metal strip in the embodiment of the present invention. This can achieve high reflectivity from the reflectors and low insertion loss. In addition, the reflectors used in the reflector 125 for the RFID tag and the reflector 130 for the temperature sensor may be an open circuit metal strip, a short circuit metal strip, an IDT type reflector, and a single bar type reflector.

The reflector 125 for the RFID tag and the reflector 130 for the temperature sensor use a multi propagation track to solve the error peak due to the multi-reflection. In an embodiment of the present invention, two propagation tracks are used to minimize signal loss, error peaks, and the like. That is, as shown in FIG. 3, a radio wave track for the reflector unit 125 for the RFID tag and a radio wave track for the reflector unit 130 for the temperature sensor are provided.

In addition, the integrated surface acoustic wave-based microsensor 100 further includes a pair of metal bars 145, an upper substrate 150, a second IDT 155, a reflector unit 160 and a support 165 for the pressure sensor. can do.

The pair of metal bars 145 are formed to be connected to the first IDT 120 on the lower substrate 110. Metal rods 145 are deposited by nickel (Ni) electroplating techniques. The metal bar 145 is installed to be connected to the second IDT 155.

The upper substrate 150 and the lower substrate 110 are formed to be sealed by a support 165 formed to surround the metal rod 145. The support 165 seals four surfaces of the left side, the right side, the upper side, and the lower side while the space between the upper substrate 150 and the lower substrate 110 is empty. The support 165 is made of a polymer such as SU-8 or JSR.

The second IDT 155 converts the RF signal received from the antenna 115 through the metal rod 145 into surface acoustic waves and propagates. The second IDT 155 converts the surface acoustic wave reflected from the pressure sensor reflector 160 into an RF signal and outputs the RF signal.

The pressure sensor reflector 160 is mounted on the upper substrate 150 by being spaced apart from the second IDT 155 by a predetermined distance, and reflects surface acoustic waves to measure the pressure to reflect the pressures 160a and 160b. 160c) (see FIG. 3). In the embodiment of the present invention, the pressure sensor reflector 160 is illustrated as having three reflectors 160a, 160b, 160c in FIG. 3, but is not limited thereto and may include various numbers of reflectors. have.

When pressure is applied to the upper substrate 150, a phenomenon occurs that occurs. This bending of the substrate causes a change in the speed and propagation distance of the SAW propagating on the upper substrate 150. The arrival time of the reflected wave by the reflector varies linearly with the degree of bending of the upper substrate 150.

According to the degree of pressure, the temperature can be compensated for from the variation of the time of the reflection peak, and then the desired pressure value can be discharged. Since the arrival time of the reflection peak changes with temperature, the correct pressure can be calculated only by compensating for the change amount of the reflection peak with respect to the current temperature.

4 shows a process of bonding the upper substrate and the lower substrate.

The support 165a surrounding the metal bar 145a is formed on the lower substrate 110, and the support 165b surrounding the metal bar 145b is formed on the upper substrate 150. The metal bar 145a has a thin and long shape, and the metal bar 145b has a thick and short shape. When the lower substrate 110 and the upper substrate 150 are bonded, the metal bar 145a and the metal bar 145b may be completely coupled to each other. The metal bar 145a and the metal bar 145b are bonded using conductive silver paste. The support 165a and the support 165b are bonded by compressing by applying heat.

Figure 5 shows the connection between the integrated surface acoustic wave-based microsensor and the network analyzer according to the present invention.

The integrated surface acoustic wave-based microsensor 100 receives RF energy from the network analyzer 500 through the analyzer side antenna 510 to measure RFID tag, temperature and pressure information, and then integrates the integrated surface acoustic wave-based microsensor. The signal measured through the antenna 115 is sent to the network analyzer 500. The antenna of the integrated surface acoustic wave-based microsensor 100 and the analyzer-side antenna 510 connected to the network analyzer 500 have a frequency band with an intermediate frequency of 2.4 GHz and maximize the wireless communication distance through impedance matching.

6 shows a graph of reflection peaks over time as seen through a network analyzer.

Reference numeral 610 denotes peaks of the signal received by being reflected from the reflector for the RFID tag, reference numeral 620 denotes peaks of the signal received by being reflected from the reflector for the temperature sensor, and reference numeral 630 denotes from the reflector for the pressure sensor. Represents the peaks of the reflected and received signal.

As shown in FIG. 6, the reflection peaks of the integrated surface acoustic wave-based microsensor according to the embodiment of the present invention have sharp waveforms and have almost the same intensity. These reflection peaks allow for relatively accurate reading of the RFID signal and accurate measurement of temperature and pressure.

Although a preferred embodiment of the present invention has been described in detail above, those skilled in the art to which the present invention pertains can make various changes without departing from the spirit and scope of the invention as defined in the appended claims. It will be appreciated that modifications or variations may be made. Accordingly, modifications to future embodiments of the present invention will not depart from the technology of the present invention.

According to the present invention, it is possible to measure the RFID tag, temperature and pressure using RF energy supplied wirelessly from the outside. The integrated surface acoustic wave-based microsensor according to the present invention is semi-permanent even in harsh environments, and is installed in an area where humans cannot directly access it due to high voltage, and thus can provide information about RFID tags, temperature, and pressure in a ubiquitous environment in real time. Can be.

Claims (9)

Lower substrate; An antenna formed on the lower substrate to wirelessly transmit and receive a pulse signal; A first inter digital transducer (IDT) for converting a pulse signal received from the antenna into surface acoustic waves and outputting the first acoustic signal; An RFID tag reflector unit spaced apart from the first IDT by a predetermined distance and mounted on the lower substrate and having a plurality of reflectors capable of reflecting the surface acoustic wave to measure radio frequency identification (RFID) information; And Integrated surface acoustic wave base, characterized in that it is mounted on the lower substrate spaced apart from the first IDT, the reflector unit for a temperature sensor having a plurality of reflectors capable of reflecting the surface acoustic wave to measure the temperature Microsensor. The method of claim 1, A pair of metal bars connected to the first IDT and formed on the lower substrate; An upper substrate installed on the metal bar; A second IDT formed on the upper substrate to convert a pulse signal received from the antenna through the metal rod into a surface acoustic wave; A reflector unit for a pressure sensor spaced apart from the second IDT and mounted on the upper substrate and having a plurality of reflectors capable of reflecting the surface acoustic wave to measure pressure; And And a support formed to surround the metal bar while supporting the upper substrate and sealing four surfaces between the upper substrate and the lower substrate. The method of claim 2, wherein the lower substrate and the upper substrate, Integrated surface acoustic wave-based microsensor, characterized in that the piezoelectric material. The method of claim 3, wherein the piezoelectric material is Integrated surface acoustic wave-based microsensor, characterized in that any one of LiNbO ₃ , LiTaO ₃ and quartz. The method of claim 2, wherein the first IDT and the second IDT, Integrated surface acoustic wave based microsensor having a single phase unidirectional transducer (SPUDT) structure. The method of claim 1, wherein the antenna, Integrated surface acoustic wave-based microsensor, characterized in that the coil is wound around the first IDT and the reflector in order to maximize the antenna length while minimizing the area occupied on the lower substrate. The method of claim 1, wherein the antenna, Integrated surface acoustic wave-based microsensor, characterized in that the intermediate frequency has a frequency band of 2.4 GHz. The reflector for an RFID tag according to claim 1, An integrated surface acoustic wave-based microsensor having one or more reflector groups composed of one or more reflectors and maximizing the number of cases of RFID by reading RFID for each of the groups. The method of claim 1, The reflector unit for the RFID tag and the reflector unit for the temperature sensor are integrated surface acoustic wave-based microsensor, characterized in that using two radio tracks.

Images