Thin film resonator and producing method therefor

Description: TECHNICAL FIELD [Detailed description of the invention]

【0001】

[Technical field to which the invention belongs]

The present invention is generally related to the field of frequency selection devices, and more specifically to thin film resonators and methods of manufacturing them.

【0002】

[Conventional technology and its problems]

Televisions and radios as well as mobile phones and other wireless devices all transmit and / or receive radio frequency signals. For example, television and radio receive programs from many stations in the form of radio frequency signals transmitted from each station. Mobile phones and other two-way wireless communication devices communicate with base stations by transmitting and receiving radio frequency signals. Radio frequency signals include voice traffic for wireless telephone connections, or data traffic for wireless Internet or other network connections.

【0003】

Televisions, radios, mobile phones and other wireless devices are assigned different radio frequencies so that they can operate simultaneously within an area. For example, a television receives signals in the range of 55 to 800 MHz (MHz), while a radio receives signals in the range of 530 to 1700 kHz (kHz) in AM and 88 to 108 MHz (MHz) in FM. Receive signals within range. Mobile phones operate in the 900 and 1800 MHz range by US standards.

【0004】

Televisions, radios, mobile phones and other wireless devices all use radio frequency filters to separate and remove unwanted radio frequency traffic from desired signals or channels. In particular, television and radio can use a number of filters to form tuners, which can be selectively tuned to their respective receivers. Mobile phones operate in a preset frequency range and have a dedicated filter in this frequency range. In either case, the filter discriminates the signal based on frequency diversity, producing a stable signal for use in the receiver.

【0005】

A resonator-based radio frequency filter consists of a pair of inductors and capacitors arranged in parallel, a crystal resonator, and a thin film resonator. The types of inductors and capacitors resonate over a wide range, resulting in poor signal discrimination quality. Quartz and thin film resonators, on the other hand, resonate in a narrow range and therefore provide high quality signal discrimination.

【0006】

A crystal resonator contains a crystal placed between a pair of columns. Quartz resonators are good at signal discrimination, but due to restrictions on crystal thickness, they are limited to applications below 500 MHz (MHz). As a result, quartz resonators are not suitable for mobile phones and other lower ultra high frequency (UHF) applications in the 300 to 3000 MHz range.

【0007】

The thin film cavity is formed on a substrate containing an acoustic reflector. The acoustic reflector can be formed of an air gap or multiple reflective layers. The thin film resonator contains a piezoelectric layer placed between two electrodes. The piezoelectric layer may contain zinc oxide (ZnO). Zinc oxide surface acoustic wave (SAW) devices have been developed as thin films over insulators. TV-IF filters are made as zinc oxide on glass.

【0008】

The piezoelectric layer has a thickness equal to half the target wavelength for the resonator to provide proper resonance of the resonator. At 900 MHz (MHz), the half wavelength is 3.5 microns. Thin film resonators are time consuming and costly to manufacture because the piezoelectric layer can only be formed at a slow rate of about 5 microns per hour due to processing constraints. In addition, the substantial thickness of the lower UHF piezo layer causes internal stress in the resonator, which leads to strain, bubbles, and crack defects.

【0009】

[Means and actions to achieve the task]

The present invention provides a thin film resonator and methods thereof that substantially reduce or eliminate the drawbacks and problems associated with the systems and methods that have been developed so far. In particular, conventional piezoelectric layers are replaced by sandwich-type layers of piezoelectric and non-piezoelectric materials that can be adhered at high speed to provide low cost, high performance thin film resonators.

【0010】

According to one embodiment of the invention, a thin film or other suitable acoustic resonator comprises a first electrode and a second electrode that are substantially parallel to each other. An intermediate layer is placed between the first and second electrodes and coupled to the first and second electrodes. The intermediate layer includes a first piezoelectric layer, a second piezoelectric layer, and a spacer layer arranged between the first piezoelectric layer and the second piezoelectric layer. The spacer layer has substantially the same acoustic impedance as the first and second piezoelectric layers and is made of a different material.

【0011】

More specifically, according to a particular embodiment of the invention, the spacer layer has a coefficient of thermal expansion that is substantially opposite to that of the first and second piezoelectric layers. In addition, the spacer layer may be designed to offset the thermal expansion of the acoustic reflector that supports the resonator.

【0012】

The technical advantage of the present invention includes providing an improved acoustic resonator and an improved filter using the acoustic resonator. In particular, the acoustic resonator includes a sandwich type of piezoelectric material and non-piezoelectric material between electrodes. The non-piezoelectric material has a substantially uniform thickness and is easily formed during production. As a result, thin films and other suitable acoustic resonators can be manufactured at low cost.

【0013】

Another technical advantage of the present invention includes providing an ultra high frequency (UHF) acoustic resonator. In particular, the non-piezoelectric spacers have a substantially uniform thickness over a wide range. As a result, the thickness of the resonator may be substantially increased to support mobile phones and other UHF applications.

【0014】

Yet another technical advantage of the present invention includes providing a stable acoustic resonator. In particular, the spacer layer may be formed of a piezoelectric layer and / or a material having thermal expansion properties opposite to that of an acoustic reflector. As a result, the stability of the resonator is increased and the device can be configured to be insensitive to temperatures within the operating range.

【0015】

Yet another technical advantage of the present invention includes providing an improved on-chip filter. In particular, a thin film resonator that can be easily manufactured directly on a substrate is provided. The resonator can be combined with other resonators to form an on-chip filter and to form an on-chip filter that is combined to form a single-chip transceiver.

【0016】

Other technical advantages of the present invention will be readily appreciated by those skilled in the art from the drawings, description, and claims below.

【0017】

[Example]

In order to better understand the present invention and its advantages, the following description will be referred to in connection with the accompanying drawings. In these drawings, similar reference numbers exhibit similar features.

【0018】

FIG. 1 shows a front-end transceiver 10 for a wireless device according to an embodiment of the present invention. In this embodiment, the wireless device is a mobile phone operating in the range of 900 MHz (MHz) according to US standards. Please be aware that the acoustic resonators and filters of the present invention may be used in connection with other types of mobile phones, wireless devices, and other suitable devices for receiving, transmitting and / or utilizing radio frequency signals. ..

【0019】

In FIG. 1, the front-end transceiver 10 includes an antenna 12, a receive filter 16, a diplexer 14 including a transmit filter 18, a power divider, a line amplifier 20, an image exclusion filter 22, a mixer 24, and a voltage. Includes a controlled oscillator (VCO) filter 26. As will be described in more detail below, one or more of the filters 16, 18, 22, and 26 can be configured with a thin film resonator with low insertion loss at radio frequencies. In this embodiment, the filters 16, 18, 22 and / or 26 can be made on-chip, i.e. directly on the underlying substrate, to form a single-chip radio. Therefore, the signal deterioration due to the bond wire connection and the capacitance of the bond pad associated with the off-chip filter is eliminated.

【0020】

The antenna 12 sends and receives signals to and from the power divider of the diplexer 14. The diplexer 14 sends an incoming signal to the receive filter 16, which, in mobile phone applications, filters out television, satellite and radio frequencies. The transmission filter 18 receives the outgoing signal and acts as a filter so that it is transmitted from the mobile phone to the base station. In response to the incoming signal, the receive filter 16 sends the resulting band-limited signal to the low noise amplifier 20. The signal is sent from the low noise amplifier 20 to the image exclusion filter 22. The image exclusion filter 22 suppresses other thermal noise in the pager, police radio and mixer 24 and the image frequency of the local oscillator.

【0021】

The image exclusion filter 22 sends a signal with further limited bandwidth to the mixer 24. The mixer 24 also receives a signal from a voltage controlled oscillator (VCO) filter 26 that is coupled to the VCO and is configured to eliminate the synthesizer pseudo-signal. The resulting in-band signal is output to the intermediate frequency (IF) chain 28 and used by the mobile phone device.

【0022】

For 900 MHz (MHz) mobile phones, the front-end transceiver 10 can use IS-95, IS-136 or GSM standards. According to IS-95 and IS-136 standards, the receive filter 16 operates in the range of 869-894 MHz, the transmit filter 18 operates in the range of 824-849 MHz, and the image exclusion filter 22 operates in the range of 869-894 MHz. The voltage controlled oscillator filter 26 operates in the 940-965 MHz range. According to GSM standards, the receive filter 16 operates in the range of 935-960 MHz, the transmit filter 18 operates in the range of 890-915 MHz, the image exclusion filter 22 operates in the range of 935-960 MHz, and the voltage controlled oscillator. Filter 26 operates in the range 1006-1031 MHz. The receive and transmit filters 16 and 18 are both 25 MHz wide.

【0023】

FIG. 2 details the filter 50 for the front-end transceiver 10 according to an embodiment of the present invention. In this embodiment, the filter 50 is a ladder type filter and is composed of a plurality of acoustic resonators 54 and 56. The ladder filter can be used for the receive filter 16, the transmit filter 18, the image exclusion filter 22 and / or the voltage controlled oscillator filter 26 of the front-end receiver 10. The ladder filter 50 can also be used in television, radio, wireless and other suitable devices that use radio frequency signals. FIG. 2 will be described in which the ladder filter 50 includes a plurality of series resonators 54 and a plurality of parallel resonators 56. A series resonator 54 is connected in series between the input terminal 60 and the output terminal 62 to form a series arm. Each of the parallel resonators 56 is connected in parallel between the series arm and the ground potential to form a parallel arm.

【0024】

In the ladder filter 50, the resonance frequency of the series resonator 54 is configured to match the antiresonance frequency of the parallel resonator 56. Therefore, the ladder type filter 50 has a pass band defined by the anti-resonance frequency of the series resonator 54 and the resonance frequency of the parallel resonator 56. The frequencies and other characteristics of the individual series and parallel resonators 54 and 56 can be varied according to the particular desired function for the filter 50.

【0025】

FIG. 3 shows details of the acoustic resonator 100 used in a ladder type or other suitable filter according to an embodiment of the present invention. In this embodiment, the acoustic resonator 100 is a thin film resonator formed directly on-chip on an acoustic reflector 102 formed directly on a substrate 104 beneath it. According to a particular embodiment, the substrate 104 comprises silicon or other suitable semiconductor material and the acoustic reflector 102 is silicon dioxide (SiO).₂) And Tungsten (W), including alternating layers with low and high acoustic impedance. Further information on the structure and materials of the acoustic reflector 102 can be found in US Patent Application No. 09 / 484,803, filed January 18, 2000, in the title of the invention "Multi-Frequency Acoustic Reflector for Resonators" Arrays and Monolithic Covers, and Methods , and are cited here for reference. In this embodiment, the resonator 100 is a solid mounted resonator. It should be understood that the resonator 100 may be via isolated, air gap isolated, or properly supported by any required substrate and then acoustically isolated.

【0026】

Referring to FIG. 3, the thin film cavity 100 includes a first electrode 110 located on the surface of the acoustic reflector 102. The second electrode 112 is arranged substantially parallel to or in the same plane as the first electrode 110, away from the first electrode 110, to provide the required quality factor. For 1 gigahertz (GHz) applications where the resonator 100 has a Q value of 1000, the distance between the first and second electrodes 110 and 112 varies by 50 angstroms or less over the entire surface of the resonator. To do. The first and second electrodes 110 and 112 are made of a metal or other suitable conductive material to be adhered as before. In certain embodiments, the electrodes 110 and 112 are each made of aluminum and have a thickness between 0.1 and 1 micron.

【0027】

An intermediate, or resonating layer 120, is placed between the first and second electrodes 110 and 112 and coupled to the first and second electrodes 110 and 112. The intermediate layer is between the first piezoelectric layer 122 coupled to the first electrode 110, the second piezoelectric layer 124 coupled to the second electrode 112, and the first and second piezoelectric layers 122 and 124. Includes spacers arranged in, i.e., the gap layer 130. To provide resonance, the intermediate layer 120 has a thickness that is half the wavelength of the target frequency of the resonator 100. Therefore, for an acoustic resonator of 900 MHz, the intermediate layer 120 has a half-wavelength thickness of about 3.5 microns.

【0028】

The first and second piezoelectric layers 122 and 124 have substantially uniform and thin thicknesses, respectively, and provide stability to minimize strain, bubbles, cracks, or other defects. In one embodiment, the first and second piezoelectric layers 122 and 124 are good while minimizing the thickness of the piezoelectric material using conventional sputtering techniques with an adhesion rate of about 5 microns per hour. Each has a thickness of about 0.5 micron so as to provide a good resonance performance. The thicknesses of the first and second piezoelectric layers 122 and 124 can be adjusted appropriately to control the Q value of the resonator 100. By independently controlling the thickness of the piezoelectric layer in this way, an additional design factor for optimizing the performance of the resonator 100 is provided. The material of the intermediate, or resonant layer, has zinc oxide (ZnO), aluminum nitride (ALN), silicon nitride (SiN), gallium arsenide (GaAs), tungsten (W), or an acceptable electromechanical coupling coefficient. Includes other suitable materials.

【0029】

The spacer 130 is substantially uniform in thickness and may form most of the thickness of the intermediate layer 120 according to the frequency of the resonator 100. The spacer layer 130 should be made of a material that can be adhered substantially uniformly, up to 3 microns or thicker, at relatively high speeds. Further, the material of the spacer layer 130 should have an acoustic impedance that is consistent with or substantially the same as the acoustic impedance of the piezoelectric layers 122 and 124. The acoustic impedances of layers 122, 124, and 130 are substantially the same when they are within 20% of each other. Furthermore, in order to provide stability to the resonator and filter 50, the thermal expansion characteristics of the spacer 130 should be the opposite of the thermal expansion characteristics of the piezoelectric layers 122 and 124. For example, aluminum nitride (ALN) has a coefficient of thermal expansion of 28 ppm / ° C, while zinc oxide (ZnO) has a thermal expansion coefficient of 60. It has a coefficient of thermal expansion of ppm / ° C. When a layer made of a material forms a structure that is generally insensitive to temperature, at least at room temperature, the material has the opposite coefficient of thermal expansion. Preferably, the device has a maximum quadratic relationship to temperature and has a zero gradient at room temperature. The material of the spacer layer 130 is silicon dioxide (SiO).₂) And aluminum (Al).

【0030】

FIG. 4 is a flowchart showing a method of manufacturing the thin film resonator 100 according to an embodiment of the present invention. In this embodiment, the resonator 100 is formed on-chip directly on the acoustic reflector 102. The acoustic resonator may be formed on other suitable supports without departing from the scope of the present invention.

【0031】

With reference to FIG. 4, this method begins with step 150 in which the substrate 104 is provided. The substrate 104 can consist of silicon, other semiconductors, or other suitable supporting material. Next, in step 152, the acoustic reflector 102 is formed on the surface of the substrate 104. The acoustic reflector 102 can be formed as described in the US patent application cited earlier for reference, the title of the invention, "Multi-Frequency Acoustic Reflector Arrays and Monolithic Covers for Resonators, and Methods."

【0032】

Proceeding to step 154, the first electrode 110 is conventionally adhered to the surface of the acoustic reflector 102. In step 156, the first piezoelectric layer 122 is adhered to the surface of the first electrode 110 using conventional sputtering or other suitable process. In step 158, the spacer layer 130 is adhered to the surface of the first piezoelectric layer 122. The spacer layer 130 is adhered by a DC plasma magnetron reactive sputtering system, electron cyclotron resonance chemical vapor deposition (ECR-CVD), and other suitable processes.

【0033】

Next, in step 160, the second piezoelectric layer 124 is adhered to the surface of the spacer layer 130. The first and second piezoelectric layers 122 and 124, together with the spacer layer 130, form a substantially uniform intermediate layer 120 and have an acoustic half-wave thickness of the desired frequency of the resonator 100. In step 162, the second electrode layer 112 is conventionally adhered to the surface of the second piezoelectric layer 124.

【0034】

Proceeding to step 164, the adhered layer is properly patterned and etched or properly processed to remove excess material to form the thin film resonator 100. In this way, low cost, high performance thin film resonance for use in wireless filters of televisions, radios, mobile phones, wireless devices, or other suitable devices that transfer, receive, and / or utilize radio frequency signals. Vessel 100 is manufactured.

【0035】

Although the present invention has been described as some examples, those skilled in the art will appreciate various modifications and modifications. The present invention is intended to cover such modifications and modifications that are included in the appended claims.

[Simple explanation of drawings]

[Figure 1]

A block diagram of a front-end transceiver for a radio frequency device according to an embodiment of the present invention.

[Figure 2]

FIG. 6 is a block diagram showing details of the filter of FIG. 1 according to an embodiment of the present invention.

[Fig. 3]

FIG. 2 is a cross-sectional view showing details of the thin film resonator of FIG. 2 according to an embodiment of the present invention.

[Fig. 4]

The flowchart which shows the method of manufacturing the thin film resonator of FIG. 3 according to one Example of this invention.

[Explanation of symbols]

100 acoustic resonator 102 Acoustic reflector 104 board 110 1st electrode 112 Second electrode 120 middle layer 122 First piezoelectric layer 124 Second piezoelectric layer 130 spacer