RU205909U1 - DUPLEXER SURFACE ACOUSTIC WAVE FILTER - Google Patents

Abstract

The utility model relates to frequency selective devices for providing simultaneous reception and transmission of information in systems with frequency division signals. The useful model makes it possible to increase the permissible power level of the input radio-frequency signal of a duplexer miniature thermostable SAW filter to a value of at least 1 W while maintaining the long-term operability of the device to the effect of a high-power RF signal with a low level of insertion loss. To achieve this task, the duplex filter contains a transmission filter and a reception filter with a common antenna, each of which has an impedance-type structure. The transmit and receive filters are formed on a piezoelectric substrate located inside a cermet body for surface mounting, where a YX1 / 42 ° cut of lithium tantalate is used as the piezoelectric substrate material. 6 h. p. f-crystals, 6 fig., 2 tab.

Description

The utility model relates to acoustoelectronics, namely, to frequency-selective devices for providing simultaneous reception and transmission of information in systems with frequency division of signals. In particular, the utility model is intended for use as part of transceiver modules of wireless communication systems of WAN (LTE, 5G), NB-IoT standards, namely, cellular telephony and cellular repeaters, which are used to solve the problem of frequency selection, i.e. transmission of one part of the radio frequency spectrum while delaying another part of it, radio frequency (RF) filters. More specifically, the utility model relates to duplexer radio frequency filters made by surface acoustic waves (SAW) technology based on piezoelectric materials. The utility model is intended for operation in the frequency range from 700 to 2500 MHz in two-channel mode with the bandwidth of each channel in the range from 10 MHz to 60 MHz, depending on the requirements of a particular standard and the isolation level of the transmitting and receiving channels not less than 40 dB.

SAW radio-frequency filters belong to acoustoelectronic devices and are the most important quality forming element of communication systems operating in the frequency range 30-3500 MHz, providing such parameters for the purpose of communication systems as range, noise immunity and information capacity. The physical principle of operation of these devices is based on the use of direct and reverse piezoelectric effects. The areas of application of RF SAW filters are: radio telephones and base stations of communication systems of LTE (Long-Term Evolution), 5G, GSM (Global System for Mobile Communications), AMPS (Advanced Mobile Phone Service), CD (Collision Detection), PHS ( Personal Handy-phone System), PCS (Personal Communications Service), CDMA (Coded Domain Multiple Access), W-CDMA; communication systems LPWAN (NB-IoT, LoRaWan), PAN (RFID); receiving and transmitting paths of GPS (Global Positioning System) and GLONASS (Global Navigation Satellite System) navigation systems; devices for the formation and processing of complex signals in long-range and short-range radar stations; onboard and ground equipment of satellite communication systems (see, for example, Gulyaev Yu. et al. "SAW filters in the input stages of transceiver devices", Science and technology in industry, 2006, No. 4, pp. 82-88; Bagdasaryan A. et al. "Frequency selection devices in modern communication systems, radar and telecommunications", Electronics, "Science, Technology, Business", 2013, No. 8, pp. 128-136).

A duplexer is a device designed to simultaneously receive information in the first frequency band (frequency channel of the receiver Ros) through the input port Rx and transmit it in the second frequency band (frequency channel of the transmitter Tx) through the input port Tx using a common port An connected to the antenna ... In this case, the frequency channels of the Rx receiver and the Tx transmitter do not intersect, which allows loading and unloading information data simultaneously and stably.

SAW duplex filters are designed to select two, as a rule, closely spaced frequency channels of the Rx receiver and the Tx transmitter in the transmitting and receiving paths of the equipment. In connection with this functional purpose, they have a number of distinctive features in comparison with bandpass filters, which complicate their design and manufacture. So, due to the proximity of the passbands of the receiver and transmitter, as well as the increased requirements for frequency selection in the adjacent channel (as a rule, not less than 40 dB), the transition bands of the amplitude-frequency characteristics (AFC) of the filters on the side of the second channel should have steep slopes, to provide the required selection.

In addition, for most applications of duplexers, a sufficiently high power (up to 1 W) is supplied to the antenna output of the transmitter and, accordingly, to the common input An of the duplexer. In the case of using the standard technology for manufacturing SAW filters, such an increased power leads to a deterioration in the long-term operability of the device due to the influence of electromigration effects in the electrodes of interdigital wave converters (IDTs). To reduce the level of electro-migration effects in the manufacture of IDTs, film layers of complex composition and structure are used (see, for example, Sinitsyna T.V. et al. “Filters on surface acoustic waves with a high input power for radio engineering communication systems: structural and technological features ", Theory and technology of radio communication, 2015, No. 3, pp. 40-45).

Also, in order to increase the duplexers' survivability to the impact of high-power RF signals, impedance-type structures are used to at least implement the Tx channel filter, having a large length of electrode structures, which ensures the distribution of the signal power over a large area of the piezoelectric substrate (see, for example, Bagdasaryan A. et al. "Impedance SAW Filters for Telecommunication Systems. Russian Priority", Electronics: Science, Technology, Business, 2014, No. 7 (139), pp. 48-65).

The constructive basis of impedance filters is a SAW resonator containing an IDT and two reflectors located in a common acoustic channel on the surface of a piezoelectric substrate. In order to achieve the required set of parameters, devices from such resonators are formed into G-, P- or T-shaped links and their subsequent connection into multi-link structures. Piezoelectric materials with a high electromechanical coupling coefficient, such as lithium niobate or lithium tantalate, are used as the substrate material. IDT and reflector electrodes can be formed from aluminum, copper, aluminum or copper alloys, gold or any other conductive material, including having a multilayer structure.

Published patent application US, 2004/0212451 discloses a SAW filter duplexer design having an impedance type structure. The known device uses a YX1 / 42 ° cut of lithium tantalate as a piezoelectric substrate material; IDT electrodes have a complex composition and geometry (Al + Cu additive; Al / Cu / Al or Al / Mg / Al), which complicates the manufacturing technology of the device. The disadvantage of the known device is that in all cases, an Al film is used as the lower layer, which does not allow reducing the level of electro-migration effects, which results in a deterioration in the long-term performance of the device.

US Pat. No. 7,038,551 discloses a SAW duplexer filter design, where the Tx channel filter is based on an impedance type structure, while the Rx channel filter is based on longitudinally coupled resonators. The prior art design limits the permissible RF input level to 0.2 watts. A YX1 / 39 ° cut of lithium tantalate was used as a piezoelectric substrate material; IDT electrodes are formed on the basis of an Al film, which impairs the long-term operability of the device to the effect of an RF signal.

US patent, 7684764 discloses a duplexer design, including two SAW filters, where the Tx channel filter has an impedance type structure, while the Rx channel filter is made on the basis of longitudinally coupled resonators, as well as a sintered body, inside which the phase matching circuits of the filters with the antenna are formed. entrance. SAW filters are implemented on a piezoelectric substrate made of YX1 / 42 ° cut of lithium tantalate. The disadvantage of the known device is that the use of a filter based on longitudinally coupled resonators for the receiver channel Rx limits the permissible level of the input RF signal with a power of 0.2 W.

до 1 мкм и пленка Al толщиной от 10

до 3 мкм, обеспечивающая подавление эффекта миграция атомов алюминия, что приводит улучшению долговременной стабильности устройства к воздействию РЧ сигнала большой мощности.US Patent 6,316,860 discloses a surface acoustic wave device that includes a YX1 / 64 ° cut lithium niobate or YX1 / 36 ° cut lithium tantalate piezoelectric substrate with interdigital structures formed thereon. For the formation of interdigital structures, a two-layer single-crystal or highly oriented in the crystallographic direction (111) polycrystalline Ti film with a thickness of 10

up to 1 micron and Al film with a thickness of 10

up to 3 microns, providing suppression of the effect of migration of aluminum atoms, which leads to an improvement in the long-term stability of the device to the influence of a high-power RF signal.

However, the cut of lithium niobate selected as a piezoelectric material YX1 / 64 ° has a temperature coefficient of frequency twice as large as compared to a piezoelectric substrate made of lithium tantalate (-72x10 ^-6 units / deg and - 36x10 ^-6 units / deg, respectively ), which significantly impairs the thermal stability of the device. Using a YX1 / 36 ° cut of lithium tantalate with a film thickness of more than 5% of the wavelength leads to an increase in the insertion loss of the device by 1-3 dB.

Thus, the hardware and system requirements for transmitting and receiving equipment necessitate a duplexer design that provides sufficient separation of RF signals between the Rx and Tx channels so that the RF signal from the transmitting Tx channel is efficiently fed to the antenna, and that the RF signal from TX channel did not penetrate the Rx receive channel, thus interfering with the received Rx channel signal. In addition, the duplexer should not attenuate the Rx channel signal received from the antenna, as this leads to a decrease in the sensitivity of the receiving path of the transceiver.

In addition, there is also a need to improve the robustness of SAW duplexer filters to high power RF signals. As noted above, one of the main reasons why SAW filters fail when a high-power signal (about 1 W) is applied is the migration of aluminum atoms between the electrodes of the interdigital converter, which occurs when the voltage is applied and the SAW passes.

This utility model is based on the task of developing such a miniature design of a thermostable SAW duplexer filter with a low level of insertion loss in a cermet case for surface mounting, which allows increasing the permissible power level of the input RF signal to a value of at least 1 W while maintaining the long-term operability of the device to RF signal of high power.

The task of developing the design of a duplexer filter on surface acoustic waves, capable of operating in the temperature range from minus 30 to + 85 ° C, is also being solved.

-5800

, а в качестве материала пьезоэлектрической подложки использован ZY7/42° срез танталата лития с величиной объемой резистивности не более 2⋅10¹⁰ Ом⋅см.The problem is solved by the fact that the duplex filter on surface acoustic waves for transceivers of wireless communication includes a transmit filter, a receive filter, each of which has an input and output, and a common antenna port, as well as a cermet body for surface mounting, inside which is located a piezoelectric substrate, on one side of which said transmission filter and reception filter are formed, as well as contact pads and switching connections, where each of said filters has an impedance type structure formed by a system of series and parallel connected resonators, each of which includes an interdigital transducer, having input and output, and two reflectors, while the resonators have a two-layer structure with a total thickness of 1000

-5800

, and a ZY7 / 42 ° cut of lithium tantalate with a resistivity volume of no more than 2⋅10 ¹⁰ Ohm⋅cm was used as a piezoelectric substrate material.

In addition, the transmit and receive filters are displaced relative to each other along the surface of one side of the piezoelectric substrate in the direction perpendicular to the direction of propagation of the surface acoustic wave.

до 5500

и нижнего слоя, выполненного из Ti либо V толщиной из диапазона от 75

до 300

.It is advisable that the two-layer resonator structures consist of an upper Al layer with a thickness ranging from 925

up to 5500

and a lower layer made of Ti or V with a thickness ranging from 75

up to 300

...

Preferably, the duplexer filter has a first capacitance matching circuit located outside the surface-mount sintered body and connected to a common antenna port.

It is also preferred that the duplexer filter has a second matching circuit located outside the surface-mount sintered body, including a combination of inductors and capacitors, and connected to the outputs of the transmit and receive channel filters.

In addition, two identical resonators connected in series are used at the input of the transmission filter connected to the common port of the antenna. At the same time, IDTs containing 2 or 3 sections connected in series are preferably used in series-connected resonators.

The essence of this useful model of a SAW duplexer filter is that both filters of the Rx and Tx channels have an impedance-type structure, which allows, due to the large number of electrodes in the IDT, to distribute the effect of the signal over a much larger area of the piezoelectric substrate and over a larger area of the IDT structure and, as a consequence, to reduce the local voltages in the electrode structures of the converter, even at high powers of the input RF signal supplied from the antenna both to the input of the Rx channel filter and to the input of the Tx channel filter, to a level of at least 1 W.

The impedance design of this duplexer filter combines the advantages of LC filters (low insertion loss - up to 2 dB, low ripple of amplitude-frequency characteristics - up to 0.5 dB and group delay time - up to 2 ns in the passband) with the advantages of SAW technology (high manufacturability and reproducibility of characteristics, small dimensions).

To reduce the level of the introduced attenuation of the filters in the passband, a YX1 / 42 ° cut of lithium tantalate is used as the material of the piezoelectric substrate, which is optimal if thick films (about 10% of the SAW length) are used to form the IDT electrode structures.

To increase the reliability of the filters to large temperature differences, the SAW duplex filter is implemented on a piezoelectric substrate with increased conductivity (volume resistivity no more than 2⋅10 ¹⁰ Ohm⋅cm), in which the level of the pyroelectric effect is negligible. When using standard piezoelectric plates, a temperature change at a rate of more than 20 deg / min leads to the appearance of electric charges and voltage surges in the piezoelectric material up to several tens of volts, which can lead to electrical breakdown of the IDT electrode structures.

до 300

не только обеспечивает адгезию пленки Al к поверхности пьезоэлектрической пластины, но и позволяет нивелировать миграционные эффекты в алюминиевых пленках, которые возникают при воздействии РЧ сигналов большой мощности. В зависимости от частотного диапазона и требуемой ширины полосы пропускания фильтра толщина пленки Al может варьироваться в диапазоне от 950

до 5500

, что обеспечивает минимальный уровень вносимого затухания.To increase the reliability of the device to high-power RF signals during the formation of IDT electrode structures, two-layer films are used, consisting of an upper Al layer and a lower layer made of Ti or V. The use of a Ti or V sublayer with a thickness of 75

up to 300

not only ensures adhesion of the Al film to the surface of the piezoelectric plate, but also makes it possible to neutralize the migration effects in aluminum films that arise when exposed to high-power RF signals. Depending on the frequency range and the required bandwidth of the filter, the Al film thickness can vary from 950

up to 5500

, which provides a minimum level of insertion loss.

To ensure the channel isolation level of at least 40 dB, the filter topologies of the Rx and Tx channels are shifted relative to each other along the surface of the piezoelectric substrate in the direction perpendicular to the direction of SAW propagation; matching circuits are also used to solve the problem of joint operation of the filters.

The essence of this SAW duplex filter is illustrated by graphic material, including the following drawings, where:

fig. 1 illustrates a block diagram of a preferred embodiment of a SAW duplexer filter;

fig. 2 illustrates the topology of a SAW resonator as the main structural element of a SAW duplexer filter;

fig. 3 illustrates a view of the working side of a piezoelectric substrate with a formed SAW duplexer filter topology, including SAW resonators, contact pads and switching connections;

fig. 4 illustrates a preferred mounting scheme for a SAW duplexer filter in a cermet SMD SMD package;

fig. 5 illustrates a preferred SAW duplexer filter matching circuit;

fig. 6 illustrates the frequency response of a SAW duplexer filter for the LTE standard.

To reveal the essence of the utility model, the following designations have been introduced in the drawings: 1 - antenna port An; 2 - SAW filter of the Rx channel; 3 - SAW filter of the Tx channel; 4 - reflector; 5 - interdigital converter (IDT); 6 - resonator; 7 - piezoelectric substrate; 8 - contact pads; 9 - cermet body for surface mounting; 10 - wire jumpers; 11 is a first antenna port matching circuit of a SAW duplexer filter; 12 - the second matching circuit for the Rx-output and Tx-input of the SAW duplexer filter.

The SAW duplex filter, according to this utility model, includes a piezoelectric substrate 7 (see Fig. 3), on which the topologies of SAW filters of the Rx 2 channel and the Tx 3 channel, united by the antenna port An 1 (see Fig. 1), and a cermet body for surface mounting 9 (see Fig. 4). For the electrical connection of the contact pads 8 with the pads of the cermet body for surface mounting 9, wire jumpers 10 are used (see Fig. 4). The input signal is fed to the antenna port An 1, then it enters the input of the filter Rx 2, where its amplitude-frequency selection takes place in the frequency range corresponding to the frequency range of the Rx 2 channel. amplitude-frequency selection in the frequency range corresponding to the frequency range of the channel Tx 3. Filters on the SAW channels Rx 2 and Tx 3 represent a system of series and parallel connected resonators R1-R10 (see Fig. 1), the fundamental structure of each of which is shown in fig. 2. Each resonator 6 consists of an interdigital converter (IDT) 5 and two reflectors 4 (see Fig. 2). The number of electrodes in the reflector and IDT is unique. To obtain the correct frequency response (see Fig. 6), a product in a cermet housing for surface mounting 9 is connected taking into account the first matching circuit 11 via the antenna port An 1 of the duplexer filter and the second matching circuit 12 via the Rx-output and Tx-output of the duplexer SAW filter (see Fig. 5). The number of matching elements at the antenna port An 1 can be increased, in particular, a series inductance can be additionally used.

The principle of forming the frequency response of the filters included in the SAW duplexer filter is based on the difference in impedances of the resonators connected in series and in parallel. Namely, in the passband of the filter, the impedance of parallel-connected resonators is high-resistance (about 850 Ohm), while for series-connected resonators, it is low-resistance (less than 10 Ohm), which makes it possible to transmit a signal from the input to the output of the device in a 50-Ohm path. no loss. In this case, at the resonance frequency, the value of the parallel resonator impedance is 1 Ohm, which provides signal rejection in the low-frequency region of the stop band. Whereas at the antiresonance frequency, the impedance of the series resonator is 1 kΩ, which provides signal rejection in the high frequency region. Thus, the impedance design combines the advantages of ZC filters (low insertion loss - up to 2 dB, low ripple of amplitude-frequency characteristics - up to 0.5 dB and group delay time - up to 2 ns in the passband) with the advantages of SAW technology (high manufacturability and reproducibility of characteristics, small dimensions).

To realize the optimal ratio of the impedances of the series and parallel resonators and improve the uniformity of the distribution of the transmitted energy over the area of the piezoelectric substrate, the resonators can be made in the form of ideal pairs of resonators connected in series and in parallel, and the filter can also have an asymmetric structure (see Fig. 1). In this case, series-connected resonators can be made using sectioned IDTs, which allows the impedance of these elements to be increased approximately fourfold. Also, to improve the squareness coefficient of the Tx channel filter from the side of the adjacent Rx channel, additional capacitors can be used to reduce the resonant gap between the resonance and antiresonance frequencies in parallel-connected resonators.

Example 1.

The essence of this utility model is illustrated by a non-limiting example of its implementation.

Structural diagram of a SAW duplex filter of the FPZP7-814-2 modification for 4G-LTE and LTE-M wireless technologies (nominal filter frequency of Tx 2 channel - 836.5 MHz; nominal filter frequency of Rx 1 channel - 881.5 MHz, bandwidth bandwidth of both channels 25 MHz) corresponds to that shown in FIG. 1. The frequencies and geometric parameters of the resonators 6 of the filters of the Tx 2 and Rx 1 channels are given in Tables 1 and 2, where the aperture corresponds to the overlap of the antiphase electrodes in the IDT 5. The material of the piezoelectric substrate 7 is a YXI / 42 ⁰ cut of lithium tantalate with increased conductivity not more than 2⋅10 ¹⁰ Ohm⋅cm. To increase the allowable power of the input RF signal to form the topology of the duplexer filter, a two-layer film of the following composition is used: h = 75A (Ti) + 4425A (Al), deposited on the working side of the piezoelectric substrate 7 by the electron-beam or high-frequency magnetron method. In this case, the total film thickness h is 10.5% of the wavelength for which the used type of material of the piezoelectric substrate is optimal, since it provides a minimum level of introduced attenuation.

The formation of the topology of the filters on the surface of the piezoelectric substrate 7 with overall dimensions of 1.9x2.7 mm is performed using the method of reverse photolithography. The electrical connection of the contact pads 8 of the filters and the pads of the cermet body for surface mounting of the SMD type 9 with overall dimensions of 3.8x3.8 mm is made using gold wire jumpers 10 in accordance with the diagram shown in FIG. 4. A typical frequency response of a SAW duplexer filter of the FPZP7-814-2 modification for 4G-LTE and LTE-M wireless communication technologies, implemented on the basis of this utility model, is shown in FIG. 6.

Table 1 illustrates the parameters of the filter resonators of the Rx 2 channel, Table 2 illustrates the parameters of the Tx 3 channel filter resonators.

The advantages of this utility model are provided by the fact that both filters of the Rx channel and the Tx channel have an impedance-type structure and are displaced relative to each other along the surface of one side of the piezoelectric substrate in a direction perpendicular to the direction of propagation of the SAW; a YXI / 42 ° cut of lithium tantalate with increased conductivity of no more than 2⋅10 ¹⁰ Ohm⋅cm was used as a piezoelectric substrate material; When forming the electrode structures of the resonators, two-layer films with an upper Al layer are used, where the lower layer is made of either Ti or V. As a result, an increase in the permissible power of the RF signal supplied to the input of the filters of the Rx and Tx channels is achieved, as well as a decrease in the level of introduced attenuation at simultaneously increasing the reliability of the device to temperature changes in the range from minus 30 ° С to + 85 ° С.

Claims (7)

1. Duplex filter on surface acoustic waves for wireless transceivers, including a transmit filter, a receive filter, each of which has an input and output, and a common antenna port, as well as a cermet body for surface mounting, inside which a piezoelectric substrate is located, on one on the side of which the said transmit filter and the receive filter are formed, as well as contact pads and switching connections, where each of the said filters has an impedance type structure formed by a system of series and parallel connected resonators, each of which includes an interdigital converter having an input and an output, and two reflectors, while the resonators have a two-layer structure with a total thickness of 1000

-5800

, and as the material of the piezoelectric substrate, a YX l / 42 ° cut of lithium tantalate with a resistivity volume of no more than 2⋅10 ¹⁰ Ohm⋅cm was used. 2. The device according to claim 1, characterized in that the transmit and receive filters are displaced relative to each other along the surface of one side of the piezoelectric substrate in a direction perpendicular to the direction of propagation of the surface acoustic wave. 3. The device according to claim 1, characterized in that the two-layer resonator structures consist of an upper Al layer with a thickness of the range from 925

up to 5500

and a lower layer made of Ti or V with a thickness ranging from 75

up to 300

... 4. The device according to claim 1, characterized in that it has a first matching circuit in the form of a capacitance located outside the cermet body for surface mounting and connected to a common antenna port. 5. The device according to claim 4, characterized in that it has a second matching circuit located outside the cermet body for surface mounting and including a combination of inductors and capacitors and connected to the outputs of the transmit and receive channel filters. 6. The device according to claim 1, characterized in that two identical resonators connected in series are used at the input of the transmission filter connected to the common port of the antenna. 7. The device according to claim 1, characterized in that in series-connected resonators, interdigital converters are used, containing 2 or 3 sections connected in series.

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