Inverted on-chip microwave power sensor and preparation method thereof

Abstract

The invention discloses a flip-chip on-chip microwave power sensor and a preparation method, the flip-chip on-chip microwave power sensor comprises a transmission substrate and a microwave power sensor, and the transmission substrate and the microwave power sensor are packaged in a flip-chip bonding mode through metal bumps; a chip of the microwave power sensor is provided with metal salient points, the transmission substrate is provided with metal pins or bonding pads matched with the metal salient points, and the metal salient points on the chip of the microwave power sensor are bonded with the metal pins or bonding pads on the substrate through heating and pressure. According to the invention, the test frequency range is 1-50GHz, the test sensitivity is high, the packaging volume is small, the integration degree is high, and the packaging test is facilitated.

Description

Technical Field

[0001] The present invention relates to a power sensor technology, and in particular to a flip-chip microwave power sensor and a preparation method thereof. Background Art

[0002] Microwave power parameter is a quantity that describes the size of microwave signals and the energy transmission characteristics of microwave signals when they pass through electronic devices. It is the most widely used basic parameter in microwave applications. It is a key parameter in many fields such as wireless communications, national defense and military industry, and atmospheric detection. In addition, the on-chip microwave power standard is also a key issue in the current microwave field. The device for measuring microwave power is a microwave power sensor. Traditional microwave power sensors use thermistors as measurement sensitive elements to measure microwave power. This method takes a long time to measure and requires regular calibration. With the development of semiconductor technology, the relevant components for microwave power measurement can be integrated into a chip processed and manufactured using semiconductor technology. It has the characteristics of fast measurement speed and high accuracy. The volume of the microwave power measurement device formed after packaging this chip will also be greatly reduced. The on-chip microwave power standard is a key technology in microwave chip technology. The continuous development and improvement of these technologies have promoted the further development and application of microwave technology. Moreover, the on-chip microwave power standard is a high-precision and high-reliability microwave measurement technology that can integrate microwave measurement devices on the chip to achieve the integration of microwave measurement and calibration. It has the advantages of reduced size, extended frequency band, and improved accuracy. In general, on-chip microwave power standards are an important research direction in microwave technology, so it is essential to develop a microwave power sensor chip with high operating frequency, low noise level and high output power.

[0003] The traditional heating-type on-chip microwave power sensor uses GaAs as the substrate, and uses a thermopile, a microwave terminal load resistor and a DC heating resistor. It eliminates heat loss through a thermally symmetrical balance structure to improve measurement accuracy. Specifically, the traditional on-chip microwave power sensor introduces the microwave signal to be measured through a coplanar waveguide, so that it is converted into thermal energy on two microwave terminal load resistors. At the same time, a DC adjustable power supply is used to heat the other end of the thermopile through a DC heating resistor. The DC power supply is adjusted to make the output voltage of the thermopile zero. At this time, the power consumed on the DC resistor is equal to the microwave power to be measured, thereby realizing the measurement of microwave power. However, since thermocouples are extremely susceptible to factors such as temperature and thermal disturbances during operation, cold-end temperature compensation and thermal disturbance correction are required. Moreover, the terminal load and thermopile arrangement of traditional microwave power chips are very limited, and electromagnetic radiation cannot be effectively avoided. Finally, when the on-chip microwave power measurement chip measures microwave power, its measurement sensitivity will be greatly reduced. The disadvantages of the prior art are:

[0004] The terminal load and thermopile of the traditional microwave power sensor are in direct contact with the external environment, which cannot prevent electromagnetic radiation problems. In such a complex environment, the test results will be greatly affected. Due to the structural limitations of the traditional microwave power sensor, the contact area between the terminal load and the thermopile is small, which will cause the thermopile to not effectively receive the heat generated by the terminal load, and the final microwave power sensitivity of the test is low. If a temperature compensation device is required, external leads need to be added to the microwave power sensor chip, which will increase the parasitic effects generated during microwave signal transmission, thereby affecting the transmission efficiency. Therefore, a flip-chip microwave power sensor and a preparation method are needed. Summary of the invention

[0005] The object of the present invention is to provide a flip-chip microwave power sensor and a preparation method thereof.

[0006] To achieve the above object, the present invention is implemented according to the following technical solutions:

[0007] The present invention comprises a transmission substrate and a microwave power sensor, wherein the transmission substrate and the microwave power sensor are packaged in the form of flip-chip bonding through metal bumps;

[0008] The chip of the microwave power sensor is provided with metal bumps, and the transmission substrate is provided with metal pins or pads matching the metal bumps. The metal bumps on the microwave power sensor chip are bonded to the metal pins or pads on the substrate by heating and pressure.

[0009] Furthermore, the microwave power sensor uses a semi-insulating gallium arsenide semiconductor material as a substrate, and a chip etching AlGaAs stop layer, a thermopile layer and a Si3N4 protective layer are sequentially arranged on the GaAs substrate.

[0010] Furthermore, an alumina ceramic substrate is arranged on the transmission substrate, and a coplanar transmission line formed of metal, a pressure welding block for outputting the thermopile voltage, and an output thermistor resistance pad are arranged on the alumina ceramic substrate.

[0011] Furthermore, a coplanar transmission line for transmitting microwave power signals is connected to an input end of the microwave power sensor, and an output end of the microwave power sensor is respectively connected to a first output welding block and a second output welding block, and the microwave power sensor comprises a transmission substrate, a first terminal load resistor and a second terminal load resistor, and the coplanar transmission line is respectively connected to the first terminal load resistor and the second terminal load resistor, and the first terminal load resistor is connected to one end of a thermocouple metal arm, and the second terminal load resistor is connected to one end of a thermocouple semiconductor arm, and the thermocouple metal arm and the thermocouple semiconductor arm are arranged alternately.

[0012] Furthermore, a surface metal layer is provided on the transmission substrate, and a plurality of metal bumps are distributed in an array on the outer side of the transmission substrate.

[0013] Furthermore, a thermistor is provided on the transmission substrate to monitor the current ambient temperature.

[0014] Furthermore, the process steps for manufacturing the microwave power sensor are as follows:

[0015] 1. Epitaxially grow 0.1um thick AlGaAs on a 625um thick undoped semi-insulating GaAs substrate as an etch stop layer;

[0016] 2. Epitaxial growth concentration is 1*1018cm -3 Highly doped GaAs is etched to form thermocouple semiconductor arm patterns

[0017] 3. Use electron beam evaporation to form 0.25um thick gold-germanium-nickel-gold, use a lift-off process to form the thermocouple metal arm pattern, and perform rapid thermal annealing to form an ohmic contact;

[0018] 4. Magnetron sputtering of 0.2um TaN, patterning by lift-off process to form terminal load;

[0019] 5. Deposit and photolithography Si3N4 to form electrical insulation between the metal layer and one end of the thermopile;

[0020] 6. Magnetron sputtering Ti / Au / Ti, using lift-off process to achieve metal patterning;

[0021] 7. Magnetron sputtering of the seed layer metal Ti / Au, thick photoresist lithography, and selective electroplating to thicken the electrode metal to 2um;

[0022] 8. Thin the substrate to 300 um, perform back overlay, and wet-etch the GaAs substrate to the AlGaAs layer to obtain the microwave power sensor.

[0023] The beneficial effects of the present invention are:

[0024] 1. The present invention uses alumina ceramic semiconductor materials on the substrate for transmitting microwave power signals. In this design, the transmission substrate first adopts a CPW coplanar waveguide transmission line with a narrower spacing, utilizing the output of high-frequency signals. Moreover, this structural design facilitates the use of GSG probes for subsequent packaging tests, and some temperature compensation devices can be added to the transmission substrate without affecting the transmission efficiency of the microwave power chip.

[0025] 2. The packaging form of the present invention can greatly improve the measurement sensitivity. The chip packaging test is carried out through metal bumps and transmission substrates, which can well reduce the parasitic effect between the microwave power sensor and the transmission substrate, thereby reducing the mismatch caused by the parasitic effect;

[0026] 3. The design of the thermopile structure of the present invention can increase the contact area between the hot end of the thermopile and the terminal load, and can absorb heat energy to a greater extent, thereby improving the measurement sensitivity;

[0027] 4. The test frequency range of the present invention is 1-50 GHz, the test sensitivity is high, and the package volume is small, the degree of integration is high, and it is convenient for packaging testing. BRIEF DESCRIPTION OF THE DRAWINGS

[0028] Figure 1 It is a schematic diagram of the overall structure of a flip-chip microwave power sensor of the present invention;

[0029] Figure 2 For the present invention Figure 1 Schematic diagram of the structure of the microwave power sensor;

[0030] Figure 3 For the present invention Figure 1 A schematic diagram of the cross-sectional structure of the microwave power sensor in FIG.

[0031] Figure 4 For the present invention Figure 1 Schematic diagram of the single pair of thermocouples of the microwave power sensor;

[0032] Figure 5 For the present invention Figure 1 Schematic diagram of the structure of seven pairs of thermocouples in the microwave power sensor. DETAILED DESCRIPTION

[0033] The present invention will be further described below in conjunction with the accompanying drawings and specific embodiments. The illustrative embodiments and descriptions of the present invention are used to explain the present invention but are not intended to limit the present invention.

[0034] The present invention comprises a transmission substrate and a microwave power sensor, wherein the transmission substrate and the microwave power sensor are packaged in the form of flip-chip bonding through metal bumps;

[0035] The chip of the microwave power sensor is provided with metal bumps, and the transmission substrate is provided with metal pins or pads matching the metal bumps. The metal bumps on the microwave power sensor chip are bonded to the metal pins or pads on the substrate by heating and pressure.

[0036] See attached Figure 1 and Figure 2As shown, a flip-chip microwave power sensor includes: a transmission substrate 20 with alumina ceramic (4mm*10mm*0.254mm) as a substrate; a coplanar transmission line 21 for microwave power signal transmission; a first output welding block 16 for the hot end voltage of the thermopile; a second output welding block 17 for the cold end voltage of the thermopile; a first output terminal 18 of the thermistor; a second output terminal 19 of the thermistor; a microwave power sensor GaAs substrate (2mm*2mm) 11; a metal bump 1 of the microwave power sensor; a microwave power signal line 2 of the microwave power sensor; a surface metal layer 7 of the microwave power sensor; a thermocouple metal arm 3; a thermocouple semiconductor arm 4; a chip etching stop layer AlGaAs 12; microwave power sensor first terminal load resistor 5; microwave power sensor second terminal load resistor 6; microwave power sensor thermopile first output welding block 8; microwave power sensor thermopile second output welding block 9; thermopile layer 13; Si3N4 protective layer 14 between the microwave power sensor thermopile and the metal layer; thermopile chip etching area 10;

[0037] The present invention includes a transmission substrate for inputting microwave power signals and outputting thermopile voltage and thermistor resistance pads; the other part is a microwave power sensor that absorbs microwave power signals to generate thermoelectric potential difference; the two are packaged in the form of flip-chip welding through metal bumps. The flip-chip welding manufacturing process includes five steps: preparing microwave power sensor chips, preparing base transmission boards, bonding, welding and packaging. In the process of manufacturing microwave power sensor chips, metal bumps need to be made on the lead-out electrodes of the chip; in the process of manufacturing substrates, metal pins or pads matching the size of the electrodes on the chip are made on the substrate. Then the microwave power sensor chip is turned upside down, and the metal bumps on the microwave power sensor chip are bonded to the metal pins or pads on the substrate, and then the chip is welded to the electrodes on the substrate by heating and pressure. Finally, the chip is packaged with packaging materials to protect the microwave power sensor chip and make it suitable for various usage scenarios.

[0038] The transmission substrate is provided with an alumina ceramic substrate, and the surface is plated with a 2um metal to form a coplanar transmission line, a thermopile voltage output welding block, and an output thermistor resistance pad. The main function of the coplanar line is to receive the input of the microwave power signal from the GSG probe; the function of the thermopile voltage output welding block is mainly to output the potential generated by the microwave power sensor chip and the output of the thermistor resistance; the function of the output thermistor resistance pad is mainly to output the resistance of the thermistor at the current ambient temperature.

[0039] like Figure 3As shown, a coplanar transmission line for microwave power signal transmission is connected to the input end of the microwave power sensor, and the output end of the microwave power sensor is respectively connected to a first output welding block and a second output welding block, and the microwave power sensor includes a transmission substrate, a first terminal load resistor and a second terminal load resistor, and the coplanar transmission line is respectively connected to the first terminal load resistor and the second terminal load resistor, the first terminal load resistor is connected to one end of a thermocouple metal arm, and the second terminal load resistor is connected to one end of a thermocouple semiconductor arm, and the thermocouple metal arm and the thermocouple semiconductor arm are arranged alternately.

[0040] The microwave power sensor that generates thermoelectric potential difference uses a semi-insulating gallium arsenide semiconductor material as a substrate, and the semi-insulating gallium arsenide semiconductor substrate is provided with an aluminum gallium arsenide barrier layer; a thermocouple metal arm and a thermocouple semiconductor arm n+GaAs; a microwave power sensor terminal load; a Si3N4 protective layer between the thermopile and the metal layer; a surface metal layer of the microwave power sensor chip; and metal bumps for interconnecting the transmission substrate and the microwave power sensor.

[0041] Main working principle: The microwave power signal is transmitted to the terminal load on the microwave power sensor through the alumina ceramic transmission substrate. The terminal load converts the microwave power signal to be measured on the alumina ceramic transmission substrate into easily measurable heat. The heat increases the temperature of the thermopile placed near the terminal load resistor, thereby generating a certain thermoelectric potential difference in the thermopile on the microwave power sensor. The thermoelectric potential difference is output through the pressure welding block that outputs the thermopile voltage. According to the output of the thermopile voltage, the microwave power at the current experimental ambient temperature (23°C) can be obtained.

[0042] How to do it:

[0043] The microwave power signal is first input through the GSG probe from the gold-plated coplanar line on the ceramic substrate, and then transmitted to the signal line on the microwave power sensor through the metal bumps. The first terminal load and the second terminal load are connected at the end of the signal line. Since the terminal load absorbs the input microwave power signal, a certain amount of heat will be generated in the terminal load and their surroundings. The temperature of the thermopile at one end close to the terminal load (called the hot end) rises, forming a certain thermoelectric potential difference with the other end of the thermopile (called the cold end). A pair of simple thermocouples composed of two materials such as Figure 4 As shown. The hot end of the thermocouple refers to the end where the ambient temperature is higher, that is, the end close to the terminal load. The cold end refers to the end where the ambient temperature is lower, usually kept at a constant temperature, and its function is to provide a reference temperature, that is, the end away from the terminal load. At this time, the two ends of the thermocouple generate a thermoelectric potential related to the temperature difference between the hot and cold ends, and its magnitude is proportional to the temperature difference. The voltage generated by the electromotive force of the thermocouple is calculated according to the following formula:

[0044] V0=α(T c -T h )

[0045] Among them, α is the temperature coefficient of the thermocouple, and its size is related to the properties of the material constituting the thermocouple; T c is the temperature of the measuring point, that is, the temperature generated by the terminal load, T h is the ambient temperature, which is also the reference temperature (23°C).

[0046] Therefore, the temperature difference between the cold end and the hot end of the thermocouple can be calculated by measuring the potential difference. In order to reduce system noise and improve the sensitivity coefficient of the system, multiple thermocouples can be connected in series to form a thermopile. A thermopile composed of multiple thermocouples is as follows: Figure 5 The voltage generated by the alternatingly connected thermopile is output through the first and second voltage output pads on the transmission substrate, which can realize the measurement of microwave power. Finally, through theoretical simulation calculation, the sensitivity coefficient of the microwave power sensor of 0.1-0.3mv / mw can be obtained at the output of the thermopile voltage pad.

[0047] The technical solution of the present invention is not limited to the above-mentioned specific embodiments. Any modification, equivalent replacement, improvement, etc. made according to the technical solution of the present invention shall fall within the protection scope of the present invention.

Claims

1. A flip-chip microwave power sensor, characterized in that: It includes a transmission substrate and a microwave power sensor, wherein the transmission substrate and the microwave power sensor are packaged in the form of flip-chip bonding through metal bumps; The chip of the microwave power sensor is provided with metal bumps, and the transmission substrate is provided with metal pins or pads matching the metal bumps. The metal bumps on the microwave power sensor chip are bonded to the metal pins or pads on the substrate by heating and pressure.

2. The flip-chip microwave power sensor according to claim 1, characterized in that: The microwave power sensor uses a semi-insulating gallium arsenide semiconductor material as a substrate, and a chip etching AlGaAs stop layer, a thermopile layer and a Si3N4 protective layer are sequentially arranged on the GaAs substrate.

3. The flip-chip microwave power sensor according to claim 1, characterized in that: An alumina ceramic substrate is arranged on the transmission substrate, and a coplanar transmission line formed by metal, a pressure welding block for outputting a thermopile voltage, and an output thermistor resistance pad are arranged on the alumina ceramic substrate.

4. The flip-chip microwave power sensor according to claim 1, characterized in that: A coplanar transmission line for transmitting microwave power signals is connected to the input end of the microwave power sensor, and the output end of the microwave power sensor is respectively connected to the first output welding block and the second output welding block. The microwave power sensor includes a transmission substrate, a first terminal load resistor and a second terminal load resistor. The coplanar transmission line is respectively connected to the first terminal load resistor and the second terminal load resistor. The first terminal load resistor is connected to one end of a thermocouple metal arm, and the second terminal load resistor is connected to one end of a thermocouple semiconductor arm. The thermocouple metal arm and the thermocouple semiconductor arm are arranged alternately.

5. The flip-chip microwave power sensor according to claim 1, characterized in that: A surface metal layer is arranged on the transmission substrate, and a plurality of metal bumps are arranged in an array distribution on the outer side of the transmission substrate.

6. The flip-chip microwave power sensor according to claim 1, characterized in that: The transmission substrate is provided with a thermistor for monitoring the current ambient temperature.

7. A method for preparing a flip-chip microwave power sensor, for preparing the flip-chip microwave power sensor according to any one of claims 1 to 6, characterized in that: The process steps for manufacturing the microwave power sensor are as follows:

1. Epitaxially grow 0.1um thick AlGaAs on a 625um thick undoped semi-insulating GaAs substrate as an etch stop layer; 2. Epitaxial growth concentration is 1*1018cm -3 Highly doped GaAs is used to etch out the thermocouple semiconductor arm pattern 3. 0.25um thick gold-germanium-nickel-gold is evaporated by electron beam, and the thermocouple metal arm pattern is formed by lift-off process, and the ohmic contact is formed by rapid thermal annealing; 4. Magnetron sputtering of 0.2um TaN, patterning by lift-off process to form terminal load; 5. Deposit and photolithography Si3N4 to form electrical insulation between the metal layer and one end of the thermopile; 6. Magnetron sputtering Ti / Au / Ti, using lift-off process to achieve metal patterning; 7. Magnetron sputtering of the seed layer metal Ti / Au, thick photoresist lithography, and selective electroplating to thicken the electrode metal to 2um; 8. Thin the substrate to 300 um, perform back overlay, and wet-etch the GaAs substrate to the AlGaAs layer to obtain the microwave power sensor.

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