CN111044799A - MEMS microwave standing wave meter based on thermoelectric and capacitive dual-channel online detection - Google Patents
MEMS microwave standing wave meter based on thermoelectric and capacitive dual-channel online detection Download PDFInfo
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Abstract
The MEMS microwave standing wave meter based on the thermoelectric and capacitive dual-channel online detection symmetrically places signal lines of an ACPS transmission line at two ends of a main transmission line as auxiliary transmission lines to form a symmetrical directional coupler; the symmetrical directional coupler respectively extracts incident microwave power and reflected microwave power to a coupling end and an isolation end of an upper branch and a lower branch; by respectively placing a thermoelectric type MEMS microwave power sensor and a capacitive type MEMS microwave power sensor on an upper branch and a lower branch, measuring microwave power of a coupling end and an isolation end of the upper branch and the lower branch, and further obtaining a standing-wave ratio; because the thermoelectric MEMS microwave power sensor is suitable for measuring smaller microwave power, and the capacitive MEMS microwave power sensor is suitable for measuring larger microwave power, the two sensors are adopted for measuring simultaneously, so that a larger dynamic range of the microwave standing wave meter can be obtained; the MEMS microwave standing wave meter has the characteristics of low loss, small chip area and compatibility with a gallium arsenide monolithic microwave integrated circuit process.
Description
Technical Field
The invention relates to an MEMS microwave standing wave meter based on thermoelectric and capacitive dual-channel online detection, in particular to a thermoelectric and capacitive dual-channel online detection MEMS microwave standing wave meter based on an MEMS (Micro-Electro-Mechanical-System) technology and a preparation method thereof.
Background
In a modern microwave high-density integrated radar system, a microwave standing wave meter is a key element for detecting a working state in a microwave system module and is used for representing the size of a standing-wave ratio in the radar system. The microwave high-density integrated radar system requires high integration of modules such as an antenna and a TR component, and is used for miniature detection, anti-interference, frequency detection and the like. Along with the fact that the size of the radar system is smaller and the integration degree is higher and higher, the highly integrated radar system is large in performance difference, difficult to measure and disassemble, and prone to component failure caused by long-term work and environmental influence, and therefore the fact that the standing-wave ratio of the radar system is detected on line is of great importance.
The method can be used for measuring under the working state of the radar system by adopting the microwave standing wave meter, the microwave standing wave meter is embedded between the amplifier and the antenna, and continuous testing can be performed. Generally, a microwave standing wave meter mainly includes two parts: the microwave signal extracting part is the microwave signal extracting part, and the microwave signal detecting part is the microwave signal extracted part. For the extraction part of the microwave signal, the structure can be divided into a structure based on a multi-port annular junction, a structure based on a sampling transmission line, a structure based on a directional coupler and the like; the detection section from which the microwave signal is extracted generally employs a diode, a logic circuit, a thermistor, and the like. However, these standing wave meters exhibit disadvantages of large size, active detection, narrow operating band, the need for additional attenuators for measuring high power, off-line detection, etc. With the rapid development of the MEMS technology, a microwave power sensor based on the MEMS technology can be adopted for a detection part of an extracted microwave signal, is used for measuring the power of the extracted microwave signal, and has the characteristics of low power consumption, miniaturization, wide frequency band, easy integration, online detection and the like. At present, microwave power sensors based on MEMS technology mainly include two types: a thermoelectric MEMS microwave power sensor and a capacitive MEMS microwave power sensor. For a thermoelectric MEMS microwave power sensor, it is based on the principle of microwave power-heat-electricity conversion; when larger microwave power is measured, the temperature of a measurement area between the load absorption resistor and the hot end of the thermopile is very high, so that the output hot voltage of the thermoelectric sensor tends to be saturated, and even the load absorption resistor or the thermopile is burnt out when the output hot voltage is very large, so that the thermoelectric MEMS microwave power sensor is more suitable for measuring smaller microwave power; for capacitive MEMS microwave power sensors, it is based on the principle of microwave power-force-electricity conversion; when the small microwave power is measured, the capacitance variation between the MEMS beam and the sensing electrode is small, so that the output capacitance variation of the capacitive sensor is small, the requirement on the precision of a testing instrument is high, and even the precision is not enough to measure, so the capacitive MEMS microwave power sensor is more suitable for measuring the large microwave power. Through literature research, the application of the microwave power sensor based on the MEMS technology in a microwave standing wave meter is still blank.
Therefore, it is urgently needed to develop a microwave standing wave meter with miniaturization, low power consumption, integration, low cost, wide dynamic range and on-line detection standing wave ratio, so as to be embedded into a microwave high-density integrated radar system, thereby realizing the standing wave ratio detection of the radar microwave system. With the intensive research of the thermoelectric and capacitive MEMS microwave power sensors, the development of the MEMS microwave standing wave meter based on the thermoelectric and capacitive dual-channel online detection for realizing the functions based on the MEMS technology becomes possible.
Disclosure of Invention
The invention aims to solve the problem that the dynamic range of the microwave power measured by the conventional microwave standing wave meter is small, and provides an MEMS microwave standing wave meter which is miniaturized, low in power consumption, integrated, low in cost, wide in dynamic range and capable of detecting the standing wave ratio on line.
In order to achieve the purpose, the method adopted by the invention is as follows: a MEMS microwave standing wave meter based on thermoelectric and capacitive dual-channel online detection adopts gallium arsenide (GaAs) as a substrate, and a CPW transmission line, an ACPS transmission line, a symmetrical directional coupler, two same thermoelectric MEMS microwave power sensors and two same capacitive MEMS microwave power sensors are arranged on the GaAs substrate:
the CPW transmission line is horizontally arranged on the GaAs substrate and is used as an input port and an output port of the MEMS microwave standing wave meter; and the CPW transmission line at the coupling port and the isolation port is used for realizing the transmission of the microwave signal on the auxiliary transmission line. The input port on the left side is a port one, the output port on the right side is a port two, the coupling port on the left side above is a port three, the isolation port on the right side above is a port four, the coupling port on the left side below is a port five, and the isolation port on the right side below is a port six. The CPW transmission line is composed of a signal line and two ground lines, wherein the ground lines are located on both sides of the signal line. In order to realize impedance matching of the port with the outside, the port characteristic impedance of the CPW transmission line is generally designed to be 50 Ω.
Two sections of ACPS transmission lines are placed on the GaAs substrate, each section of ACPS transmission line is composed of a signal line and a ground line, and the signal line of the ACPS transmission line is used as a secondary transmission line of a symmetrical directional coupler in the MEMS microwave standing wave meter. The signal lines of the two sections of ACPS transmission lines are symmetrically positioned at the upper side and the lower side of the main transmission line in the symmetrical directional coupler, and the lengths of the signal lines are quarter wavelengths. In the symmetrical directional coupler, two ends of each section of auxiliary transmission line are respectively a coupling end and an isolation end, wherein the coupling end is close to the input end, and the isolation end is close to the output end. In order to achieve impedance matching in connection with the CPW transmission line, the characteristic impedance of the ACPS transmission line is designed to be 50 Ω.
The symmetrical directional coupler is positioned among input, output, coupling and isolating ports of the MEMS microwave standing wave meter and mainly comprises a main transmission line and two auxiliary transmission lines, wherein the two auxiliary transmission lines are positioned on the upper side and the lower side of the main transmission line, and the distances from the two auxiliary transmission lines to the main transmission line are equal. And a capacitive MEMS microwave power sensor is arranged on the upper auxiliary transmission line, and a thermoelectric MEMS microwave power sensor is arranged at the tail end of the subsequent CPW transmission line of the lower auxiliary transmission line.
Each capacitive MEMS microwave power sensor mainly comprises an MEMS clamped beam, a CPW transmission line and Si3N4The sensor comprises an insulating medium layer, a sensing electrode, a connecting wire, an air bridge and a pressure welding block.
Two same MEMS clamped beams are placed at the connection nodes of the CPW transmission line and the ACPS transmission line of the branch above the symmetrical directional coupler; the MEMS clamped beam stretches over the CPW signal line, and two ends of the MEMS clamped beam are fixed on the CPW ground lines on two sides of the CPW signal line through anchor areas; the MEMS clamped beam is a suspended clamped beam structure provided with through holes at equal intervals, and the through holes on the MEMS clamped beam are beneficial to releasing the clamped beam. The left side and the right side of a CPW signal line below the MEMS clamped beam are respectively provided with a sensing electrode, and the sensing electrodes are interconnected with an external pressure welding block by adopting a connecting line; the interconnection of the CPW ground wires separated by the connecting wires is completed above the connecting wires by adopting an air bridge; simultaneously, the CPW signal wire below the sensing electrode, the connecting wire and the MEMS clamped beam is covered with Si3N4And an insulating dielectric layer.
Two load matching resistors are respectively arranged at the tail ends of the coupling end and the isolation end of the upper branch of the symmetrical directional coupler to complete the impedance matching of the CPW transmission line of the upper branch, the resistance values of the load matching resistors are both 100 omega, and Si is covered above the load matching resistors3N4And an insulating dielectric layer.
Each thermoelectric MEMS microwave power sensor mainly comprises a CPW transmission line, a thermopile, a pressure welding block, two load absorption resistors and Si3N4The MEMS substrate film structure comprises an insulating medium layer and an MEMS substrate film structure.
Four same load absorption resistors are arranged on the coupling port and the isolation port of the lower branch of the symmetrical directional coupler in pairs. The coupling port and the isolation port are connected with two load absorption resistors in parallel, and the resistance values are both 100 omega. Two identical thermopiles are respectively placed close to, but not in contact with, the load absorption resistances. Each thermopile is formed by connecting ten pairs of thermocouples in series, each pair of thermocouples comprises a semiconductor arm anda metal arm, and connected together at one end using a metal connecting wire. Covering the thermopile and the load absorption resistor with Si3N4And the insulating medium layer is used for playing a role in protecting in the preparation process. The MEMS substrate film structure is positioned below the load absorption resistor and the hot end of the thermopile, and a part of the GaAs substrate below the MEMS substrate film structure is removed through an MEMS back etching technology to form the MEMS substrate film structure, so that the heat transmission efficiency from the load absorption resistor to the hot end of the thermopile is improved, and the temperature difference between the hot end and the cold end of the thermopile is improved.
Two air bridges are arranged at two connection nodes of the CPW transmission line and the ACPS transmission line of the branch below the symmetrical directional coupler to connect the separated CPW ground wires, the air bridges cross over the CPW signal lines, two ends of the air bridges are connected to the CPW ground wires at two sides through anchor areas, and Si covers the CPW signal lines below the air bridges3N4And an insulating dielectric layer.
In the mechanical structure, the CPW transmission line, the ACPS transmission line, the symmetrical directional coupler, the capacitive MEMS microwave power sensor and the thermoelectric MEMS microwave power sensor are positioned on the same GaAs substrate.
The MEMS microwave standing wave meter based on the thermoelectric and capacitive dual-channel online detection is formed by adopting a fully passive structure, wherein a symmetrical directional coupler couples incident microwave power on a main transmission line to coupling ends of an upper branch and a lower branch through two sections of ACPS auxiliary transmission lines and couples reflected microwave power to isolation ends of the upper branch and the lower branch; the ratio of incident microwave power to reflected microwave power can be obtained by analyzing the microwave power received by the coupling end and the isolation end, and then the standing-wave ratio is obtained; wherein the microwave power extracted by the upper branch is measured by using a capacitive MEMS microwave power sensor; two connecting nodes of the CPW transmission line and the ACPS transmission line of the upper branch respectively span an MEMS clamped beam, the clamped beam is fixed on the ground lines at two sides through anchor areas, sensing electrodes are arranged at two sides of the CPW signal line to sense the change of capacitance between the MEMS clamped beam and the sensing electrodes caused by microwave power transmission, so that microwave power respectively received by a coupling end and an isolation end of the upper branch can be detected; the microwave power extracted by the lower branch is measured by a thermoelectric MEMS microwave power sensor; respectively arranging a thermoelectric MEMS microwave power sensor at the tail ends of a coupling end and an isolating end of a lower branch, wherein when microwave power is transmitted to the coupling end and the isolating end of the lower branch, the microwave power is finally absorbed by a load absorption resistor at the tail end of a CPW transmission line to generate heat, so that the temperature around the load absorption resistor is increased, thermocouples placed near the load absorption resistor respectively measure the temperature difference, and thermoelectric force output is generated on an output pressure welding block of a thermopile based on the Seebeck effect, so that the microwave power respectively received by the coupling end and the isolating end of the lower branch is measured; the capacitance type MEMS microwave power sensor adopted by the upper branch is suitable for measuring larger microwave power, and the thermoelectric type MEMS microwave power sensor adopted by the lower branch is suitable for measuring smaller microwave power, so that the microwave standing wave meter has a wider dynamic range by combining the measurement results of the upper branch and the lower branch.
The invention relates to a preparation method of an MEMS microwave standing wave meter based on thermoelectric and capacitive dual-channel online detection, which adopts a gallium arsenide monolithic microwave integrated circuit and an MEMS process, and the preparation method comprises the following specific processing steps:
(1) selecting a gallium arsenide epitaxial wafer as a substrate, wherein the gallium arsenide substrate is semi-insulating and the resistivity of the epitaxial layer is 100-130 omega/□; coating photoresist, removing the photoresist in the region outside the semiconductor arm of the thermocouple, etching the front epitaxial layer, and then removing the photoresist to form the semiconductor arm of the thermopile;
(2) sputtering AuGeNi/Au, completely forming a metal arm of the thermopile by adopting a stripping process, preliminarily forming a pressure welding block, and then carrying out rapid thermal annealing to ensure that the semiconductor arm and the metal arm have good ohmic contact;
(3) wet etching the semiconductor arm of the thermopile to reduce the thickness of the semiconductor arm, so that the resistance of the thermopile is increased to about 300K omega;
(4) coating photoresist on the GaAs substrate obtained in the step (3), removing the photoresist at the position where the load absorption resistor and the load matching resistor are prepared to be manufactured, sputtering to grow TaN, and stripping to form the load absorption resistor and the load matching resistor of 25 omega/□;
(5) coating photoresist on the GaAs substrate obtained in the step (4), removing the photoresist at the positions of preparing the CPW transmission line, the ACPS transmission line, the sensing electrode and the connecting line, growing a layer of Ti/Pt/Au/Ti in an evaporation mode, and preliminarily forming the CPW transmission line and the ACPS transmission line by adopting a stripping process to completely form the sensing electrode and the connecting line;
(6) growing a layer 2300 Å thick Si by plasma enhanced chemical vapor deposition3N4Insulating dielectric layer, photoetching and etching Si3N4An insulating medium layer, Si retained on the thermopile, the load absorption resistor, the load matching resistor, the sensing electrode, the connecting line, the CPW signal line below the MEMS clamped beam of the upper branch circuit and the CPW signal line below the air bridge of the lower branch circuit3N4An insulating dielectric layer;
(7) spin-coating a polyimide sacrificial layer with the thickness of 1600nm, photoetching and etching the polyimide sacrificial layer, and reserving the polyimide sacrificial layer below the air bridge and the MEMS clamped beam to be prepared;
(8) evaporating the seed layer Ti/Au/Ti for electroplating, photoetching and removing the photoresist at the position to be electroplated;
(9) growing a layer of Au on the seed layer obtained in the step (8) in an electroplating mode, removing photoresist at a position where electroplating is not needed, reversely etching Ti/Au/Ti, and corroding bottom gold to completely form structures such as a CPW transmission line, an ACPS transmission line, an MEMS clamped beam, an air bridge, a pressure welding block and the like;
(10) coating a layer of photoresist on the front surface of the substrate for protection, and carrying out operation on the back surface of the GaAs substrate;
(11) coating a layer of photoresist on the back surface of the GaAs substrate, photoetching the photoresist, removing the photoresist below the load absorption resistor and the hot end of the thermopile, and performing wet etching on the back surface of the GaAs substrate to form an MEMS substrate film structure, wherein the thickness of the MEMS substrate film structure is less than 20 microns;
(12) and (3) removing the front protection material, scribing the front of the substrate, corroding the sacrificial layer manufactured in the step (7) by using a developing solution, releasing the MEMS clamped beam and the air bridge, slightly soaking by using deionized water, dehydrating by using absolute ethyl alcohol, volatilizing at normal temperature, and airing.
Has the advantages that:
compared with the prior art, the MEMS microwave standing wave meter based on the thermoelectric and capacitive dual-channel online detection has the following advantages:
(1) in the structure, the incident microwave power and the reflected microwave power are respectively coupled to the coupling end and the isolation end of the upper branch and the lower branch by designing a symmetrical directional coupler, and microwave power sensors with different characteristics are adopted on the upper branch and the lower branch for measurement, so that the dynamic range of the microwave standing wave meter is expanded;
(2) in the structure, two identical capacitance MEMS microwave power sensors are used for measuring the microwave power coupled by an upper branch, and two identical thermoelectric MEMS microwave power sensors are used for measuring the microwave power coupled by a lower branch; the capacitive MEMS microwave power sensor is suitable for measuring larger microwave power, and the thermoelectric MEMS microwave power sensor is suitable for measuring smaller microwave power.
(3) The MEMS microwave standing wave meter adopts a symmetrical directional coupler based on CPW and ACPS transmission lines to replace the traditional structure based on microstrip lines, so that the extraction of incident microwave power and reflected microwave power is realized, the microwave standing wave meter can have lower microwave loss in a higher frequency band, and other devices can be conveniently connected in series and in parallel because a signal line and a ground line are on the same plane.
(4) The MEMS microwave standing wave meter based on the thermoelectric and capacitive dual-channel online detection is an online device, and most microwave signals can still be used in the measurement process, so that the standing wave ratio is detected online; the preparation method is compatible with a gallium arsenide monolithic microwave integrated circuit.
Drawings
FIG. 1 is a schematic diagram of a MEMS microwave standing wave meter based on a pyroelectric and capacitive two-channel online detection;
FIG. 2 is a cross-sectional view A-A of a MEMS microwave standing wave meter based on a pyroelectric and capacitive two-channel online detection;
FIG. 3 is a B-B section of a MEMS microwave standing wave meter based on a pyroelectric and capacitive two-channel online detection;
FIG. 4 is a C-C section of a MEMS microwave standing wave meter based on a pyroelectric and capacitive two-channel online detection;
the figure includes: CPW transmission line 1, ACPS transmission line 2, symmetrical directional coupler 3, thermoelectric MEMS microwave power sensor 4, capacitive MEMS microwave power sensor 8, Si3N4The MEMS device comprises an insulating medium layer 12, a metal arm 13, a semiconductor arm 14, a load absorption resistor 15a, a load matching resistor 15b, bonding pads 16a and 16b, a sensing electrode 17, air bridges (18 a and 18 b), an MEMS clamped beam 19, a connecting wire 20, a GaAs substrate 21, an MEMS substrate membrane structure 22, a port I21, a port II 22, a port III 23, a port IV 24, a port V25 and a port VI 26.
Detailed Description
The invention relates to a specific implementation scheme of an MEMS microwave standing wave meter based on thermoelectric and capacitive dual-channel online detection, which comprises the following steps:
the GaAs substrate 21 is provided with a CPW transmission line 1, an ACPS transmission line 2, a symmetrical directional coupler 3, two identical thermoelectric MEMS microwave power sensors 4 and two identical capacitive MEMS microwave power sensors 8.
The CPW transmission line 1 is horizontally arranged on the GaAs substrate 21 and is used as an input port and an output port of the MEMS microwave standing wave meter; and the CPW transmission line 1 at the coupling port and the isolation port is used for realizing the transmission of the microwave signal on the auxiliary transmission line. The input port on the left side is port one 31, the output port on the right side is port two 32, the coupled port on the left side above is port three 33, the isolated port on the right side above is port four 34, the coupled port on the left side below is port five 35, and the isolated port on the right side below is port six 36. The CPW transmission line 1 is composed of a signal line and two ground lines, wherein the ground lines are located at both sides of the signal line. In order to realize impedance matching of the port with the outside, the port characteristic impedance of the CPW transmission line 1 is generally designed to be 50 Ω.
Two sections of ACPS transmission lines 2 are placed on a GaAs substrate 21, each section of ACPS transmission line 2 is composed of a signal line and a ground line, wherein the signal line of the ACPS transmission line 2 is used as a secondary transmission line of a symmetrical directional coupler 3 in the MEMS microwave standing wave meter. The signal lines of the two sections of ACPS transmission lines 1 are symmetrically positioned at the upper side and the lower side of the main transmission line in the symmetrical directional coupler 3, and the lengths of the signal lines are quarter wavelengths. In the symmetric directional coupler 3, two ends of each section of secondary transmission line are respectively a coupling end and an isolation end, wherein the coupling end is close to the input end and the isolation end is close to the output end. In order to achieve impedance matching in connection with the CPW transmission line 1, the characteristic impedance of the ACPS transmission line 2 is designed to be 50 Ω.
The symmetrical directional coupler 3 is positioned between the input port, the output port, the coupling port and the isolation port of the MEMS microwave standing wave meter, and mainly comprises a section of main transmission line and two sections of auxiliary transmission lines, wherein the two sections of auxiliary transmission lines are positioned on the upper side and the lower side of the main transmission line, and the distances from the two sections of auxiliary transmission lines to the main transmission line are equal. The capacitive MEMS microwave power sensor 8 is arranged on the upper auxiliary transmission line, and the thermoelectric MEMS microwave power sensor 4 is arranged at the tail end of the subsequent CPW transmission line of the lower auxiliary transmission line.
Each capacitance type MEMS microwave power sensor 8 mainly comprises an MEMS clamped beam 19, a CPW transmission line 1 and Si3N4Insulating medium layer 12, sensing electrode 17, connecting wire 20, air bridge 18b and bonding pad 16 a.
Two same MEMS clamped beams 19 are placed at the joint of the CPW transmission line 1 and the ACPS transmission line 2 of the branch above the symmetrical directional coupler 3; the MEMS clamped beam 19 crosses over the CPW signal line, and two ends of the MEMS clamped beam 19 are fixed on the CPW ground lines on two sides of the CPW signal line through anchor areas; the MEMS clamped beam 19 is a suspended clamped beam structure provided with through holes at equal intervals, and the through holes on the MEMS clamped beam 19 are beneficial to releasing the clamped beam. The left side and the right side of a CPW signal line below the MEMS clamped beam 19 are respectively provided with a sensing electrode 17, and the sensing electrodes are interconnected with an external pressure welding block 16a by adopting a connecting line 20; the interconnection of the CPW ground lines separated by the connecting lines 20 is accomplished using air bridges 18b above the connecting lines 20; meanwhile, the CPW signal wire below the sensing electrode 17, the connecting wire 20 and the MEMS clamped beam 19 is covered with Si3N4An insulating dielectric layer 12.
Two load matches are respectively placed at the coupling end and the isolation end of the upper branch of the symmetrical directional coupler 3The resistance 15b completes the impedance matching of the upper branch CPW transmission line 1, the resistance values of the load matching resistors 15b are all 100 omega, and Si is covered above the load matching resistors 15b3N4An insulating dielectric layer 12.
Each thermoelectric MEMS microwave power sensor 4 mainly comprises a CPW transmission line 1, a thermopile, a pressure welding block 16b, two load absorption resistors 15a and Si3N4An insulating dielectric layer 12 and a MEMS substrate membrane structure 22.
Four identical load absorption resistors 15a are placed on the coupling port and the isolation port of the lower branch of the symmetrical directional coupler 3 in pairs. The coupling port and the isolation port are both connected in parallel with two load absorption resistors 15a, and the resistance values are both 100 Ω. Two identical thermopiles are respectively placed close to, but not in contact with, the load absorption resistance 15 a. Each thermopile is formed by ten pairs of thermocouples connected in series, each pair comprising a semiconductor arm 14 and a metal arm 13 and connected at one end using a metal connecting wire. The thermopile and the load absorption resistor 15a are covered with Si3N4And the insulating medium layer 12 is used for protecting in the preparation process. The MEMS substrate film structure 22 is positioned below the load absorption resistor 15a and the hot end of the thermopile, and a part of the GaAs substrate 21 below the MEMS substrate film structure is removed through an MEMS back etching technology to form the MEMS substrate film structure 22, so that the transmission efficiency of heat from the load absorption resistor 15a to the hot end of the thermopile is improved, and the temperature difference between the hot end and the cold end of the thermopile is improved.
Two air bridges 18a are arranged at two connection nodes of the CPW transmission line 1 and the ACPS transmission line 2 of the lower branch of the symmetrical directional coupler 3 to connect with the separated CPW ground wires, the air bridges 18a cross over the CPW signal wires, two ends are connected with the CPW ground wires at two sides through anchor areas, and Si covers the CPW signal wires below the air bridges3N4An insulating dielectric layer 12.
In terms of mechanical structure, the CPW transmission line 1, the ACPS transmission line 2, the symmetric directional coupler 3, the capacitive MEMS microwave power sensor 8, and the thermoelectric MEMS microwave power sensor 4 are located on the same GaAs substrate 21.
The MEMS microwave standing wave meter based on the thermoelectric and capacitive dual-channel online detection is formed by adopting a fully passive structure, wherein a symmetrical directional coupler 3 couples incident microwave power on a main transmission line to coupling ends of an upper branch and a lower branch through two sections of ACPS auxiliary transmission lines, and couples reflected microwave power to isolation ends of the upper branch and the lower branch; the ratio of incident microwave power to reflected microwave power can be obtained by analyzing the microwave power received by the coupling end and the isolation end, and then the standing-wave ratio is obtained; wherein the microwave power extracted by the upper branch is measured by a capacitive MEMS microwave power sensor 8; two connecting nodes of the CPW transmission line and the ACPS transmission line of the upper branch respectively span an MEMS clamped beam 19, the clamped beams are fixed on ground lines at two sides through anchor areas, sensing electrodes 17 are arranged at two sides of the CPW signal line, and the change of capacitance between the MEMS clamped beam 19 and the sensing electrodes 17 caused by microwave power transmission is sensed, so that microwave power respectively received by a coupling end and an isolation end of the upper branch can be detected; the microwave power extracted by the lower branch is measured by a thermoelectric MEMS microwave power sensor 4; respectively arranging a thermoelectric MEMS microwave power sensor 4 and the tail ends of a coupling end and an isolating end of a lower branch, wherein when microwave power is transmitted to the coupling end and the isolating end of the lower branch, the microwave power is finally absorbed by a load absorption resistor 15a at the tail end of a CPW transmission line 1 to generate heat, so that the temperature around the load absorption resistor 15a is increased, thermocouples placed near the load absorption resistor 15a respectively measure the temperature difference, and thermoelectric force output is generated on an output pressure welding block of a thermopile based on the Seebeck effect, so that the microwave power received by the coupling end and the isolating end of the lower branch respectively is measured; because the capacitance type MEMS microwave power sensor 8 adopted by the upper branch is suitable for measuring larger microwave power, and the thermoelectric type MEMS microwave power sensor 4 adopted by the lower branch is suitable for measuring smaller microwave power, the microwave standing wave meter has wider dynamic range by combining the measuring results of the upper branch and the lower branch.
The invention relates to a preparation method of an MEMS microwave standing wave meter based on thermoelectric and capacitive dual-channel online detection, which adopts a gallium arsenide monolithic microwave integrated circuit and an MEMS process, and the preparation method comprises the following specific processing steps:
(1) selecting a gallium arsenide epitaxial wafer as a substrate, wherein the gallium arsenide substrate is semi-insulating and the resistivity of the epitaxial layer is 100-130 omega/□; the photoresist is applied, the photoresist is removed in the area outside the semiconductor arms of the thermocouples, the front epitaxial layer is etched, and then the photoresist is removed to form the semiconductor arms 14 of the thermopiles.
(2) Sputtering AuGeNi/Au, completely forming the metal arm 13 of the thermopile by adopting a stripping process, preliminarily forming the bonding pads 16a and 16b, and then carrying out rapid thermal annealing so that the semiconductor arm 14 and the metal arm 13 have good ohmic contact.
(3) The semiconductor arms 14 of the thermopile are wet etched to reduce their thickness, increasing the resistance of the thermopile to around 300K omega.
(4) And (4) coating photoresist on the GaAs substrate 21 obtained in the step (3), removing the photoresist on the positions where the load absorption resistor 15a and the load matching resistor 15b are prepared, sputtering to grow TaN, and stripping to form the load absorption resistor 15a and the load matching resistor 15b of 25 omega/□.
(5) And (4) coating photoresist on the GaAs substrate 21 obtained in the step (4), removing the photoresist at the positions of the CPW transmission line 1, the ACPS transmission line 2, the sensing electrode 17 and the connecting line 20 to be manufactured, growing a layer of Ti/Pt/Au/Ti in an evaporation mode, and preliminarily forming the CPW transmission line 1 and the ACPS transmission line 2 by adopting a stripping process to completely form the sensing electrode 17 and the connecting line 20.
(6) Growing a layer 2300 Å thick Si by plasma enhanced chemical vapor deposition3N4Insulating dielectric layer, photoetching and etching Si3N4An insulating medium layer, Si retained on the thermopile, the load absorption resistor 15a, the load matching resistor 15b, the sensing electrode 17, the connecting wire 20, the CPW signal line below the MEMS clamped beam 19 of the upper branch and the CPW signal line below the air bridge 18a of the lower branch3N4An insulating dielectric layer 12;
(7) spin-coating a polyimide sacrificial layer with the thickness of 1600nm, photoetching and etching the polyimide sacrificial layer, and reserving the polyimide sacrificial layer below the air bridges 18a and 18b and the MEMS clamped beam 19 to be manufactured;
(8) evaporating the seed layer Ti/Au/Ti for electroplating, photoetching and removing the photoresist at the position to be electroplated;
(9) growing a layer of Au on the seed layer obtained in the step (8) in an electroplating mode, removing photoresist at the position where electroplating is not needed, reversely etching Ti/Au/Ti, and corroding bottom gold to completely form structures such as a CPW transmission line 1, an ACPS transmission line 2, an MEMS clamped beam 19, air bridges 18a and 18b, pressure welding blocks 16a and 16b and the like;
(10) coating a layer of photoresist on the front surface of the substrate for protection, and carrying out operation on the back surface of the GaAs substrate 21;
(11) coating a layer of photoresist on the back surface of the GaAs substrate 21, photoetching the photoresist, removing the photoresist below the load absorption resistor 15a and the hot end of the thermopile, and performing wet etching on the back surface of the GaAs substrate 21 to form an MEMS substrate film structure 22, wherein the thickness of the MEMS substrate film structure is less than 20 microns;
(12) and (3) removing the front-side protective material, scribing the front side of the substrate, corroding the sacrificial layer manufactured in the step (7) by using a developing solution, releasing the MEMS clamped beam 19 and the air bridges 18a and 18b, slightly soaking the MEMS clamped beam and the air bridges 18a and 18b by using deionized water, dehydrating by using absolute ethyl alcohol, volatilizing at normal temperature, and airing.
The criteria for distinguishing whether this structure is present are as follows:
(1) the transmission of microwave signals is realized by adopting a CPW transmission line 1 and an ACPS transmission line 2 which are horizontally arranged.
(2) The symmetrical directional coupler 3 is adopted to couple the incident microwave power to the two coupling ends and couple the reflected microwave power to the two isolation ends.
(3) Two capacitance MEMS microwave power sensors 8 are respectively arranged on the coupling end and the isolation end of the upper branch.
(4) Two thermoelectric MEMS microwave power sensors 4 are respectively arranged at the tail ends of the CPW transmission line 1 at the coupling end and the isolation end of the lower branch.
(5) At the capacitive MEMS microwave power sensor 8 structure: the MEMS clamped beam 19 spans the CPW signal line, two ends of the MEMS clamped beam are fixed on the CPW ground line through anchor areas, two sensing electrodes 17 are arranged on two sides of the CPW signal line below the MEMS clamped beam 19, the sensing electrodes 17 are connected with bonding pads 16a on the outer side of the CPW transmission line 1 through connecting lines 20, and the CPW ground lines separated by the connecting lines 20 are interconnected through air bridges 18 b.
(6) At the thermoelectric MEMS microwave power sensor 4 structure: the tail end of the CPW transmission line is provided with a load absorption resistor 15a, a thermopile structure consisting of a metal arm 13 and a semiconductor arm 14 is arranged close to the outer side of the load absorption resistor 15a, pressure welding blocks 16b are arranged at two ends of the thermopile, and an MEMS substrate film structure 22 is designed at the load absorption resistor 15a and the hot end of the thermopile.
(7) And the tail ends of the CPW transmission lines of the upper branch coupling end and the isolation end are provided with load matching resistors 15b to realize impedance matching of the isolation end.
(8) An air bridge 18a is arranged at the connecting node of the CPW transmission line and the ACPS transmission line of the lower branch so as to interconnect the cut CPW ground wires.
(9) The CPW signal line 1 under the load absorption resistor 15a, the load matching resistor 15b, the sensing electrode 17, the thermopile and the MEMS clamped beam 19 is covered with Si3N4An insulating dielectric layer 12;
the structure meeting the above conditions is regarded as the MEMS microwave standing wave meter based on the thermoelectric and capacitive dual-channel online detection.
Claims (3)
1. MEMS microwave standing wave meter based on thermoelectric type and capacitanc binary channels on-line measuring, its characterized in that: the MEMS microwave power sensor comprises a GaAs substrate (21), wherein a CPW transmission line (1), an ACPS transmission line (2), a symmetrical directional coupler (3), two load matching resistors (15 b), two thermoelectric MEMS microwave power sensors (4) and two capacitive MEMS microwave power sensors (8) are arranged on the GaAs substrate (21); the symmetrical directional coupler (3) is composed of a transmission line and two auxiliary transmission lines, wherein the two auxiliary transmission lines are positioned on two sides of the main transmission line in parallel and have equal distances to the main transmission line; microwave power is transmitted to a main transmission line of the symmetrical directional coupler (3) from an input port, incident microwave power of a port I (31) is coupled to a port III (33) and a port V (35) through two auxiliary transmission lines respectively, and the inverse of the port II (32) is coupledMicrowave power is coupled to port four (34) and port six (36), respectively; a coupling end and an isolation end of a branch above the symmetrical directional coupler (3) are respectively provided with a capacitive MEMS microwave power sensor (8), and the tail ends of the coupling end and the isolation end of the branch below the symmetrical directional coupler (3) are respectively connected with a thermoelectric MEMS microwave power sensor (4); each thermoelectric MEMS microwave power sensor (4) comprises a CPW transmission line (1), two load absorption resistors (15 a), an MEMS substrate film structure (22) and a thermopile; the thermopile is composed of a semiconductor arm (14) and a metal arm (13), wherein the semiconductor arm (14) is made of N+Gallium arsenide, the metal arm (13) is AuGeNi/Au alloy; said thermopile being placed close to, but not in contact with, the load-absorbing resistor (15 a); each thermopile is formed by connecting ten pairs of thermocouples in series, each pair of thermocouples comprises a semiconductor arm (14) and a metal arm (13), and one ends of the thermocouples are connected by using a metal connecting wire, and two sides of each thermopile are respectively connected with a pressure welding block (16 b); a MEMS substrate film structure (22) is formed by digging a cavity on the back of the GaAs substrate (21) near the load absorption resistor (15 a) and the hot end of the thermopile; each capacitive MEMS microwave power sensor (8) comprises an MEMS clamped beam (19), a CPW transmission line (1), a sensing electrode (17), a connecting line (20), an air bridge (18 b) and a pressure welding block (16 a); the MEMS clamped beam (19) crosses over the CPW signal line, two ends of the MEMS clamped beam are fixed on the CPW ground line through anchor areas, two sensing electrodes (17) are symmetrically arranged on two sides of the CPW signal line below the MEMS clamped beam (19), and the sensing electrodes (17) are interconnected with an external pressure welding block (16 a) by adopting a connecting wire (20); an air bridge (18 b) is adopted above the connecting wire (20) to realize interconnection of CPW ground wires separated by the connecting wire (20); si covers the thermopile, the load absorption resistor (15 a), the load matching resistor (15 b), the connecting wire (20), the MEMS clamped beam (19) and the CPW signal wire and the sensing electrode (17) below the air bridge3N4An insulating dielectric layer (12).
2. The MEMS microwave standing wave meter based on thermoelectric and capacitive dual-channel online detection as claimed in claim 1, wherein: the symmetrical directional coupler (3) comprises a CPW transmission line (1) and two ACPS transmission lines (2), wherein a signal line of the CPW transmission line (1) forms a main transmission line of the symmetrical directional coupler (3), and two signal lines of the two ACPS transmission lines (2) form two auxiliary transmission lines of the symmetrical directional coupler (3); the signal lines of the two sections of ACPS transmission lines (2) are symmetrically distributed on the upper side and the lower side of the main transmission line, wherein the length of each section of ACPS transmission line (2) is one quarter wavelength.
3. The MEMS microwave standing wave meter based on thermoelectric and capacitive dual-channel online detection as claimed in claim 1, wherein: the two capacitive MEMS microwave power sensors (8) are identical, and the two thermoelectric MEMS microwave power sensors (4) are identical; in the upper branch of the symmetrical directional coupler (3), the tail end of each capacitive MEMS microwave power sensor (8) is connected with two load matching resistors (15 b) in parallel, in the lower branch of the symmetrical directional coupler (3), two air bridges (18 a) are arranged between the ACPS auxiliary transmission line and the thermoelectric MEMS microwave power sensor (4), each air bridge (18 a) crosses over the CPW signal line of the lower branch, and two ends of each air bridge are respectively fixed on the CPW ground lines on two sides of the CPW signal line through anchor areas.
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