CN212991103U - Microwave emitter - Google Patents

Abstract

The utility model relates to a microwave communication technical field, concretely relates to microwave emitter, include: a package base; at least one radio frequency amplifier chip connected to the package base; the radio frequency amplifier chip comprises a substrate and a transistor; the transistor comprises an epitaxial layer covering the substrate; the substrate includes a first layer of synthetic diamond having an average thermal conductivity, a radio frequency power combining chip connected to the package base, and a second layer of synthetic diamond disposed proximate the transistor. The utility model discloses a microwave transmitter improves the performance of the radio frequency amplifier module and equipment that are used for communication between land, space and the airborne entity.

Description

Microwave emitter

Technical Field

The utility model relates to a microwave communication technical field, concretely relates to microwave emitter.

Background

Today's efficient coding algorithms are the target of many communication system designers, which results in a significant increase in the efficiency of the modulation bandwidth used in microwave communications: for 4G cellular technology, from less than 1 bit/sec/hz, to 30 bit/sec/hz. In order to maintain a high aggregate data rate transmission over appreciable distances, the signal-to-noise ratio must remain large. It is clear that the channel capacity depends on the signal-to-noise ratio for a given channel bandwidth, no matter how well the coding is. This ratio is limited by the maximum practical power that the transmitter can transmit at the high end of the signal power and the receiver sensitivity and propagation distance at the low end. The receiver sensitivity is determined by the input device noise figure and the received in-band noise, which in turn depends on the receiver bandwidth. In many applications, the upper power limit is not regulated, but rather determined by the required propagation distance and the required bandwidth, or generally by practicality. For systems and aerospace applications where signals are intended to be transmitted over long distances, the output power of the amplifier may range from kilowatts to hundreds of kilowatts. The design of radio frequency and microwave transmitters that emit such energy is a challenge.

SUMMERY OF THE UTILITY MODEL

The utility model provides a microwave transmitter for improve the performance that is used for the radio frequency amplifier module and the equipment of communication between land, space and the airborne entity.

In order to achieve the above object, the utility model provides a following technical scheme: a microwave launcher comprising: a package base; at least one radio frequency amplifier chip connected to the package base; the radio frequency amplifier chip comprises a substrate and a transistor; the transistor comprises an epitaxial layer covering the substrate; the substrate includes a first layer of synthetic diamond having an average thermal conductivity, a radio frequency power combining chip connected to the package base, and a second layer of synthetic diamond disposed proximate the transistor.

Preferably, the substrate is characterized by a thickness between 50.mu.m and 300. mu.m.

Preferably, the average value of the thermal conductivity is more than 1000W/mK.

Preferably, the transistor is an AlGaN/GaN high electron mobility transistor.

Preferably, the epitaxial layer includes a two-dimensional electron gas layer, and the electron gas layer is located at a distance of not more than 150nm from the substrate.

Preferably, the transistor further comprises a plurality of parallel transistor gates arranged on the transistor, wherein the average interval between the gates in the direction perpendicular to the gates is less than 25 μm.

The utility model discloses beneficial effect: a microwave transmitter is disclosed to improve the performance of radio frequency amplifier modules and apparatus for communication between terrestrial, space and airborne entities. Microwave amplifiers based on the GaND technology include an active region (AlGaN/GaN field effect transistor) and passive elements disposed on a synthetic diamond substrate. The thermal conductivity of diamond is incomparable with other materials known to man: depending on the manufacturing conditions, the thermal conductivity is between 800 and 2200 watts/km. In the high-power AlGaN/GaN field effect transistor, diamond is used as a substrate material instead of sapphire, silicon or silicon carbide, so that the thermal resistance of the device can be reduced by 2-3 times. The diamond disperses the heat generated by the amplifier to the lower part of the device, thereby greatly reducing the overall thermal resistance of the device. Thermal diffusion is most pronounced in small electronic devices, where the lateral dimensions of the device are on the order of the thickness of the substrate or greater. For example, high electron mobility AlGaN/GaN transistors operating in the X-band and above have a unit gate width of 100 μm and are shorter due to microwave performance. In such devices, it is important to use a diamond substrate rather than a conventional substrate to improve its thermal performance. Compared with GaN/SiC, the thermal conductivity and output power of the GaND chip are improved by 2 to 3 times. In addition, the present application discloses a high power amplifier having reduced size and weight relative to the prior art. This is particularly important for mobile and portable communication devices. While having a longer communication range for the same weight and size, i.e., for a given size and weight of the high power amplifier, the disclosed chip results in an amplifier data transfer rate that is higher than that using prior art amplifiers, as compared to the prior art.

Drawings

In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings used in the description of the embodiments or the prior art will be briefly described below, it is obvious that the drawings in the following description are only some embodiments of the present invention, and for those skilled in the art, other drawings can be obtained according to these drawings without creative efforts.

FIG. 1 is a cross-sectional view of an AlGaN/GaN transistor using gallium nitride on diamond (GaND) technology;

fig. 2 is a top view of a high power rf amplifier module according to a second embodiment of the present invention;

fig. 3 is a cross-sectional view of an AlGaN/GaN transistor using gallium nitride technology in accordance with the present invention.

Detailed Description

The technical solution of the present invention will be described clearly and completely with reference to the accompanying drawings of the present invention, and obviously, the described embodiments are only some embodiments of the present invention, not all embodiments. Based on the embodiments in the present invention, all other embodiments obtained by a person skilled in the art without creative efforts belong to the protection scope of the present invention.

The first embodiment is as follows:

referring to fig. 1, a cross-sectional view of an additional monolithically integrated microwave or millimeter wave circuit (MMIC)400 using gan d technology is shown. The MMIC chip 412 attached to the package base or flange 406 includes an epitaxial layer 405 disposed on the substrate 404, connected to the package base 406 using a solder layer 408, the package base being the portion of the package to which the chip is attached; most of the heat generated by the chip is typically dissipated through the package base. The MMIC chip 412 comprises an epitaxial layer 405, said epitaxial layer 405 in turn comprising passive and active electronic devices 416 and 401, respectively, in or on said epitaxial layer 405. Where the active circuit 401 is an output transistor, aspects of the thermal improvements possible using the gan d technique may be understood with reference to the electrical contacts 402, 403 and 410 associated with the output transistor 401. The high electron mobility transistor (HEW)401 or Heterostructure Field Effect Transistor (HFET) is also referred to as comprising source 402, gate 403 and drain 410 terminals, the active 402, gate 403 and drain 410 terminals being arranged on the epitaxial layer 405, the epitaxial layer 405 containing a two-dimensional source of electron gas (2DEG)411 embedded in the epitaxial layer 405 arranged on the substrate 404. The transistor 401 operates by controlling a current flowing along the 2DEG411 between the source 402 and the drain 410 using a voltage applied between the gate 403 and the source 402. The 2DEG region of the gate voltage control current is under the gate 403 terminal. The crystalline layers above and below the 2DEG411 are commonly referred to as barrier layer 415 and buffer layer 414, respectively. The epitaxial layer 405 includes each of the two crystalline layers and the 2DEG 411. Buffer layer 414 may comprise more than one layer of different materials, as is known in the art.

During operation of the transistor, most of the heat is dissipated in region 409 of epitaxial layer 405. The challenge in achieving a highly thermally efficient transistor is that the structure is able to conduct heat dissipation from the region 409 to the outside world through the substrate 404 and the package base 406. Most of the heat flows from the location of generation 409 through buffer layer 414 and substrate 404 to package base 406 and then through package base 406 and surface 413 to a heat conducting or dissipating element (not shown in fig. 1) attached to surface 413. Some of the heat diffusion and flow directions are indicated by arrows 407. The goal of efficient transistor chip thermal design is to reduce the thermal resistance between the heat source 409 and the backside 413 of the package base 406. In the present invention, the thermal resistance of the output transistors of the amplifier (whether MMIC or power transistor bar array) is defined as the difference between the peak temperature of the transistors in region 409 and the average temperature of the back face 413 of the package base 406, divided by the power consumed at the output transistor or transistors during normal operation. Other definitions of thermal resistance are sometimes used by the industry, which do not include the package base, nor do they specify a peak temperature of the package base to the thermally conductive element, rather than an average temperature, which can be used as a means of comparison between designs. The thermal resistance of the transistor shown in fig. 1 is determined in part by the sum of the temperature drop contributions in the different layers (or structures) that the heat in must travel from the active layer 409 to the thermally conductive element under the package (attached to surface 413). The physical factors that determine the thermal resistance of the structure shown in fig. 1 are directly proportional to the thermal conductivity of the material and the distance the heat must travel, and inversely proportional to the effective cross-sectional area through which the heat must travel. From the heat generating region 409, heat first has to pass through the buffer layer 414, which is composed of bulk GaN having thermal conductivity. The kappa is about 130W/mK. The barrier layer 415 (above the 2DEG) is composed of ternary and quaternary alloys of AlGaN, InGaN, and InAlGaN, which have a lower thermal conductivity than GaN due to alloy scattering, but contribute less to thermal conductivity than the buffer layer. Since the use of GaN material is determined by the choice of transistor type, while the overall size of the active layer is determined by the desired transistor performance and the desired output power, the desired reduction in thermal resistance of the buffer layer is achieved primarily by optimizing the thickness of the buffer layer. In conventional GaN transistors fabricated in a single epitaxial growth on a substrate (such as silicon carbide, silicon or sapphire), an interfacial layer must be grown on top of the substrate before growing the buffer layer, since these substrates exhibit a non-negligible lattice mismatch with GaN. The interfacial layer must absorb dislocations generated by growth on the lattice mismatched substrate. Even with the interface layer, the crystal quality is not sufficient to grow a high quality 2 DEG. Since GaN tends to self-heal during growth, eventually creating a surface, the surface quality of the buffer layer on which the 2DEG is to be grown is improved by increasing the thickness of the buffer layer-the number of dislocations is less for thicker buffer layer films. Thus, the buffer layer in conventional GaN transistors is between 500nm and 2000nm thick, which greatly increases the thermal resistance of the structure. The thickness of the substrate is the optimum thickness for thermal diffusion when compared to smaller heat source size, unit gate width, but also depends on mechanical stability. GaN-on-diamond-hemt shows performance advantages over competing technologies at all frequencies, but the advantages are more pronounced at frequencies in the X-band and greater when the unit gate width is less than 100 um. For frequencies in the Ka band, the unit gate width is 50 um. For these reasons, in one embodiment, the thickness of the synthetic diamond layer under the transistor or synthetic diamond substrate is set in a range between 50um to 300um by device design and fabrication. The high substrate thermal conductivity of GaN-on-diode transistors further reduces the gate-to-gate spacing, which in turn further increases the RF output power per unit wafer transistor bar width or MMIC chip width. In one embodiment, the gate-to-gate spacing of the transistors is less than 25 urn.

In gallium nitride transistors on diamond, the buffer layer is not grown on the substrate, but is bonded to the diamond substrate. Prior to this bonding process step, the original growth substrate (for GaN epitaxial layers) and the corresponding interface layer are removed, exposing the back surface of the buffer layer (the surface facing the substrate in fig. 1). One method for bonding the two materials is to grow a synthetic diamond substrate on the back of the buffer layer plated with the nanometer thin dielectric layer. When the bottom surface of the buffer layer is exposed, it is also thinned prior to diamond bonding to optimize thermal performance. This process is not simple because very thin layers are prone to cracking and instability due to embedded strain. However, thermally optimal buffer layer thicknesses can be achieved, allowing the fabrication of devices with high thermal conductivity. The thickness of the buffer layer depends on the thermal properties of the interface between the synthetic diamond substrate and the buffer layer. When the buffer layer thickness is less than 150nm, a significant improvement can be achieved compared to conventional transistors. In one embodiment, the distance between the 2DEG and the substrate is set by device design and fabrication to be less than 150 nm.

In one embodiment, an epitaxial layer stack with a fully or partially completed electronic or optical device is connected to a substrate with high thermal conductivity. In another embodiment, the substrate is made of synthetic diamond, and in yet another embodiment, the electronic device is an AlGaN/GaN High Electron Mobility Transistor (HEMT), also known in the industry as a Heterostructure Field Effect Transistor (HFET).

In one embodiment, synthetic diamond is grown on the back of a blank epitaxial layer prepared for the fabrication of electronic or optical devices. In yet another embodiment, the electronic device is an AlGaN/GaN High Electron Mobility Transistor (HEMT), also known in the industry as a Heterojunction Field Effect Transistor (HFET).

On top of another structure of the transistor, as part of a diamond coating. The purpose of the diamond layer is to extract heat up from the device and then spread the heat laterally across the device, being absorbed by areas of the substrate not directly below the transistors. In another embodiment, the substrate is made of synthetic diamond.

As shown in fig. 3, the millimeter wave technology is shown monolithically or integrated with a millimeter wave integrated circuit. The MMIC chip 712 is disposed on a substrate 704, which substrate 704 is connected to a package base 706 using a solder layer 708, which package base 706 includes an epitaxial layer 705 (which may include a stack of component epitaxial layers). The package base is the portion of the package to which the chip is attached through which most of the heat is dissipated.

Example two:

an illustration of a simplified top view of a packaged single-stage RF amplifier module according to fig. 2. Packaged RF amplifier 600 includes a flange 601 having an elevated edge 602 surrounding the interior of the package, an RF input lead 603, and an RF output lead 604. Visible at the bottom of the interior of the package is a package base 605. The RF signal is directed from input RF conductor 103 to output RF conductor 104. RF input leads that extend into the interior of the package first pass the RF signal to the microstrip RF combiner chip 607, which functions to convert the external transmission impedance to the input impedance of the transistor stick chip and to split the input power into multiple identical transistor stick chips 606. For simplicity, the packaged RF amplifier 600 is shown with only two identical transistor-stick chips 606, the transistor-stick chips 606 being combined with combiner chips 607 and 610, although there may of course be more in other embodiments. The output signals from each of the transistor stick chips 606 are combined and coupled to the output RF lead 604 using the power combiner chip 610. The microstrip combiner pattern 611, configured on the output power combiner chip 610, is used to combine the power from each transistor stripe 606 and convert the transistor impedance to the impedance of the external transmission line (impedance transformation pattern not shown). The bottom of the package interior 605 is the package base to which the chip 606 is connected using solder or a high thermal conductivity epoxy. In one embodiment, at least one of the combiner chips 607 or 608 is connected to the package base 605. Using the GaND technique to form the chips 606, the combiner is tuned to handle higher power, reduced in size if necessary, and optionally constructed of higher thermal conductivity materials to further assist in heat dissipation due to the subsequent low thermal resistance and therefore higher output power capability of each chip 606. In one embodiment, the RF power combiner is used in the same RF amplifier system optimized for use with GaN on diamond amplifier chips. In one embodiment, the output power RF combiner is a waveguide combiner. One of the reasons why the thermal conductivity and thermal conductivity of GaN substrates fabricated based on this process are reduced is that the thermal conductivity of the substrate is reduced. In one embodiment, the package base is made of synthetic diamond.

In yet another embodiment, an amplifier system is located within a housing containing a plurality of radio frequency amplifier modules, each module comprising a package, at least one input port, at least one output port, at least one radio frequency amplifier chip connected to the package, the radio frequency amplifier chip comprising at least one electronic device configured on an epitaxial layer overlying a substrate, an RF power combiner coupled to the output port, and a thermally conductive element, wherein the substrate comprises a first layer of synthetic diamond having an average thermal conductivity value. In yet another embodiment, the average thermal conductivity of the synthetic diamond is 1000W/mK.

The above description is only for the specific embodiments of the present invention, but the protection scope of the present invention is not limited thereto, and any person skilled in the art can easily think of the changes or substitutions within the technical scope of the present invention, and all should be covered within the protection scope of the present invention. Therefore, the protection scope of the present invention shall be subject to the protection scope of the claims.

Claims (6)

1. A microwave launcher, comprising:

a package base;

at least one radio frequency amplifier chip connected to the package base;

the radio frequency amplifier chip comprises a substrate and a transistor;

the transistor comprises an epitaxial layer covering the substrate;

the substrate includes a first layer of synthetic diamond having an average thermal conductivity, a radio frequency power combining chip connected to the package base, and a second layer of synthetic diamond disposed proximate the transistor.

2. A microwave launcher according to claim 1, wherein: the substrate is characterized by a thickness between 50.mu.m and 300. mu.m.

3. A microwave launcher according to claim 2, wherein: the average value of the thermal conductivity is more than 1000W/mK.

4. A microwave launcher according to claim 3, wherein: the transistor is an AlGaN/GaN high electron mobility transistor.

5. A microwave launcher according to claim 4, wherein: the epitaxial layer includes a two-dimensional electron gas layer located no more than 150nm from the substrate.

6. A microwave launcher according to claim 5, wherein: further comprising a plurality of parallel transistor gates disposed on the transistors, wherein the average spacing between the gates in a direction perpendicular to the gates is less than 25 μm.

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