Photoelectric integrated sensing chip for photoelectric volume pulse wave blood pressure measurement

Abstract

An optoelectronic integrated sensing chip for photoelectric volume pulse wave blood pressure measurement, from the top view of the chip, comprising four light emitting areas, light detection area, light emitting area contact electrode, light detection area contact electrode, light emitting area pressure welding electrode, light detection area pressure welding electrode, the isolation layer between four relatively independent light emitting areas and light detection area is isolated from each other. The application integrates the light emitting area and the light detection area of the photoelectric volume pulse wave sensor on a chip, the module volume is small, and the integration is convenient; the light emitting area and the detection area have the same resonant cavity and active area, the selectivity of wavelength is good, and the anti-interference ability of the device is improved; since the chip adopts the resonant cavity structure, the light emitting brightness of the light emitting area is high, the efficiency of the light detection area is high, the driving current required by the whole device is small, the power consumption is low, and it is convenient to apply to wearable medical equipment.

Description

Technical Field

[0001] This invention relates to an optoelectronic integrated sensor chip for photoplethysmography (PPG) blood pressure measurement, belonging to the field of semiconductor optoelectronics. Background Technology

[0002] In the field of non-invasive continuous blood pressure monitoring, traditional photoplethysmography (PPG) sensors have great application potential in smart wearable devices and other blood pressure health monitoring equipment due to their non-invasiveness, low power consumption, and lack of electromagnetic interference. They utilize photoelectric signals to detect changes in the volume of blood vessels in the human body to measure blood pressure. A PPG sensor mainly consists of two parts: an LED light source and a photodetector. Its working process involves the LED emitting monochromatic light of a specific wavelength towards the fingertip. The light beam is absorbed by various human tissues such as the skin, venules, and arteries, and reflected back to the body surface. The photodetector then receives the light signal and converts it into an electrical signal, commonly known as the PPG signal. Based on the PPG signal, changes in blood volume within the blood vessels can be determined, thereby measuring blood pressure. Traditional photoplethysmography (PPG) sensors have the following drawbacks: 1. Due to the need to penetrate some human tissue, traditional PPG sensors require LED light sources with high power consumption and short standby time to achieve good signal acquisition, which is not conducive to wearable applications; 2. The LED light source and photodetector of traditional PPG sensors are two separate and independent components. When assembled together, they are not only bulky but also expensive, making them unsuitable for wearable devices; 3. The luminous efficiency of the LED light source used in traditional PPG sensors is not high due to isotropic spontaneous emission, electrode light blocking, uneven lateral current spread, and strong light absorption by the substrate; 4. The photodetector area of ​​traditional PPG sensors usually adopts an APD or PIN structure, with a wide spectral response range. However, the photodetector current is affected by human movement trajectory and ambient stray light, resulting in poor anti-interference capability of the sensor. To enable the detector to respond only to light emitted by a selected LED light source and enhance its anti-interference capability, a signal conditioning circuit needs to be added to the front end of the detector. This will not only increase the cost of the system, but also increase the size and complexity of the system. Summary of the Invention

[0003] The purpose of this invention is to propose an optoelectronic integrated sensor chip for photoplethysmography (PPG) blood pressure measurement, so as to simultaneously solve the four shortcomings of the traditional PPG sensor and realize a small-sized, high-efficiency, strong anti-interference, and low-power PPG sensor integrated chip.

[0004] The present invention relates to an optoelectronic integrated sensor chip for photoplethysmography (PPG) blood pressure measurement.

[0005] See Figure 1 From a top view of the chip, it includes a first light-emitting region 101, a second light-emitting region 201, a third light-emitting region 301, a fourth light-emitting region 401, a photodetector region 501, contact electrodes 102 of the light-emitting regions, contact electrodes 502 of the photodetector regions, bonding electrodes 103 of the light-emitting regions, bonding electrodes 503 of the photodetector regions, and an isolation layer 600 that isolates the light-emitting regions and the photodetector regions from each other. See also... Figure 2 ,along Figure 1 Viewed in a vertical cross-section along the AA' direction, the structure includes an upper Bragg reflector 700, a resonant cavity 800, a lower Bragg reflector 900, a substrate 002, and a lower electrode 001. The resonant cavity 800 contains an active region 801. The upper Bragg reflector 700 is composed of alternating layers of relatively low-refractive-index material 701 and relatively high-refractive-index material 702, each with a thickness of 1 / 4 of the optical wavelength. The lower Bragg reflector 900 is also composed of alternating layers of relatively low-refractive-index material 901 and relatively high-refractive-index material 902, each with a thickness of 1 / 4 of the optical wavelength.

[0006] When the chip is operating, the bonding electrode 103 in the light-emitting area is positively charged relative to the lower electrode 001, while the bonding electrode 503 in the photodetector area is negatively charged relative to the lower electrode 001. The current injected from the bonding electrode 103 is transported via the contact electrode 102 to the first light-emitting area 101, the second light-emitting area 201, the third light-emitting area 301, and the fourth light-emitting area 401. Then, radiative recombination occurs in the active area 801 along a vertical direction. The light radiation is selected by the resonant cavity 800 and emitted outside the chip, illuminating the target under test. Part of the light illuminating the target is reflected back to the photodetector area 501. This reflected light is absorbed by the active area 801 of the photodetector area and converted into photocurrent after the resonant cavity 800 improves the detectivity. When the blood volume in the human microvessels changes, the blood's absorption coefficient of light changes, resulting in a relative change in the reflected light received by the photodetector area, and consequently, a relative change in the photocurrent. This pulsatile change in blood volume contains a wealth of cardiovascular physiological information, so the device can be applied to medical blood pressure measurement.

[0007] The optoelectronic integrated sensor chip for photoplethysmography (PPG) blood pressure measurement described in this invention has several important advantages over traditional PPG sensors, namely:

[0008] 1. The overall size of the optoelectronic integrated sensor chip module for photoplethysmography (PPG) blood pressure measurement is reduced, making it easier to wear.

[0009] Because the device described in this invention integrates the LED light source and photodetector area of ​​a traditional photoplethysmography (PPG) sensor onto the same chip, the light-emitting area is forward-biased to emit directional light, and the photodetector area is reverse-biased to achieve the photodetection function. By integrating both functions into a single chip, the size of the module is greatly reduced, the overall cost is lowered, and it is easier to make the device wearable.

[0010] 2. Strong anti-interference ability

[0011] Since the light emitting region and the light detecting region have the same resonant cavity (800) and active region (801) structure, after applying a forward bias voltage to the light emitting region and a reverse bias voltage to the light detecting region, the radiation spectrum of the light emitting region and the absorption spectrum of the light detecting region are exactly matched. This results in good wavelength selectivity and can suppress interference from human motion trajectories and stray light from the environment that are not within the resonant wavelength range. This effectively improves the device's anti-interference capability and stability against noise such as ambient light.

[0012] 3. High luminous brightness, high efficiency, and low power consumption.

[0013] Because the chip of this invention adopts an optical micro-resonant cavity structure composed of an upper Bragg reflector 700, a resonant cavity 800 and a lower Bragg reflector 900, the light emission brightness of the light emission region is high; the active region thickness of the photodetector region is much smaller than that of the active region of the traditional PIN structure, the transit time of photogenerated carriers in the active region is greatly reduced, and the efficiency of the photodetector region is high; the entire device requires a small driving current and has low power consumption, making it easy to apply in wearable medical devices. Attached Figure Description

[0014] Figure 1 Top view of an optoelectronic integrated sensor chip for photoplethysmography (PPG) blood pressure measurement.

[0015] Figure 2 Cross-sectional view of an optoelectronic integrated sensor chip for photoplethysmography (PPG) blood pressure measurement.

[0016] Figure 1 In the diagram, 101 is the first light emitting region, 201 is the second light emitting region, 301 is the third light emitting region, 401 is the fourth light emitting region, 501 is the light detection region, 102 is the contact electrode of the light emitting region, 502 is the contact electrode of the light detection region, 103 is the bonding electrode of the light emitting region, 503 is the bonding electrode of the light detection region, and 600 is the isolation layer that isolates the light emitting region and the light detection region from each other.

[0017] Figure 2In the diagram, 700 is the upper Bragg mirror, 800 is the resonant cavity, 801 is the active region, 900 is the lower Bragg mirror, 002 is the substrate, and 001 is the lower electrode. The upper Bragg mirror 700 is composed of alternating layers of relatively low-refractive-index material 701 and relatively high-refractive-index material 702, each with a thickness of 1 / 4 of the optical wavelength. Similarly, the lower Bragg mirror 900 is composed of alternating layers of relatively low-refractive-index material 901 and relatively high-refractive-index material 902, each with a thickness of 1 / 4 of the optical wavelength. Detailed implementation method:

[0018] Take, for example, an optoelectronic integrated sensor chip with a wavelength of 660nm for measuring blood pressure using photoplethysmography (PPG).

[0019] The first light emitting region (101), the second light emitting region (201), the third light emitting region (301), the fourth light emitting region (401), and the light detection region (501) are separated by an isolation layer (600).

[0020] Separately, the insulating layer material can be SiO2 or Si3N4 insulating material.

[0021] The contact electrode (102) of the light emitting region and the contact electrode (502) of the light detecting region are made of Ti / Au.

[0022] The upper Bragg reflector (700), the resonant cavity (800), and the lower Bragg reflector (900) together form an optical micro-resonant cavity whose cavity size is on the same order of magnitude as the wavelength of the resonant cavity.

[0023] When the chip is working, the bonding electrode (103) of the light-emitting region is positively charged relative to the lower electrode (001), and the bonding electrode (503) of the photodetector region is negatively charged relative to the lower electrode (001). The light-emitting region is forward biased to emit directional light, and the photodetector region is reverse biased to achieve photodetection. Since the light-emitting region and the photodetector region have the same resonant cavity (800) and active region (801) structure, the radiation spectrum of the light-emitting region matches the absorption spectrum of the photodetector region after the bias voltage is applied. The full width at half maximum (FWHM) changes by only 0.33 nm with the increase of current, reaching a maximum of 100 nm.

[0024] At 13.263nm, its full width at half maximum (FWHM) is more stable than that of ordinary LEDs.

[0025] The fabricated device has a voltage of only 2.1V at an operating current of 20mA; first light emitting region (101), second light emitting region (201), third light emitting region (301).

[0026] The fourth light-emitting region (401) can observe visible red light at a minimum of 2 μA;

[0027] When 1 mA is injected, the device optical power reaches 0.21 mW, and the external quantum efficiency is 10.9%.

[0028] 1. Growth of epitaxial wafers:

[0029] On an N-type GaAs substrate 002, an N-doped under-Bragg mirror 900 is epitaxially grown sequentially using metal-organic chemical vapor deposition (MOCVD). The low-refractive-index material 901 and the high-refractive-index material 902 are AlAs and Al₂O₃, respectively. 0.5 Ga 0.5 As, the resonant cavity 800 and the active region 801, the active region is made of GaInP / (Al) 0.5 Ga 0.5 ) 0.5 In 0.5 The structure consists of a p-multiple quantum well structure, followed by a p-doped upper Bragg mirror 700, where the low-refractive-index material 701 and the high-refractive-index material 702 are AlInP and (Al2O3)2, respectively. 0.3 Ga 0.7 ) 0.5 In 0.5 P, thus obtaining the resonant cavity epitaxial sheet.

[0030] 2. Chip fabrication process steps:

[0031] a. Cleaning the epitaxial wafer: Sonicate in an ultrasonic instrument for 10 minutes, then place it in beakers containing acetone and ethanol respectively, and heat it twice on a heating stage at 140℃. Then rinse it repeatedly with deionized water 30 times, and finally dry it with a nitrogen gun.

[0032] b. Etching Isolation Trench 600: After cleaning and drying, the substrate is grown with a SiO2 layer of appropriate thickness using plasma-enhanced chemical vapor deposition (PECVD) as a mask layer. Then, isolation trench 600 is etched down to the substrate position using photolithography and inductively coupled plasma etching (ICP). At this point, the substrate is divided into two independent regions: the first light-emitting region 101, the second light-emitting region 201, the third light-emitting region 301, the fourth light-emitting region 401, and the photodetector region 501.

[0033] c. Filling the isolation medium 601: Using plasma-enhanced chemical vapor deposition (PECVD) and photolithography, an insulating material such as SiO2 or Si3N4 with the same thickness as the channel depth is deposited in the etched isolation trench to fill the isolation medium 601, so that it is on the same horizontal plane as the first light emitting region 101, the second light emitting region 201, the third light emitting region 301, the fourth light emitting region 401 and the photodetector region 501.

[0034] d. Fabrication of P-side electrodes: Windows are etched on the dielectric isolation layer 601 using photolithography and inductively coupled plasma etching (ICP) processes. Then, Ti / Au of 150 / 60001 is grown by magnetron sputtering. Finally, contact electrodes 102 and 502, as well as bonding electrodes 103 and 503, are formed by electrode stripping process.

[0035] e. Perform substrate thinning.

[0036] f. Long N-face electrode 001: The Au / Ge / Ni under-face electrode 001 is formed by sputtering or electron beam evaporation.

[0037] g. Alloy annealing: Anneal at 430°C for 40 seconds to achieve good ohmic contact.

[0038] h. Divide and cleave to obtain individual cores.

Claims

1. An optoelectronic integrated sensor chip for photoplethysmography (PPG) blood pressure measurement, which, from a top view, includes a light emitting region, comprising a first light emitting region (101), a second light emitting region (201), a third light emitting region (301), and a fourth light emitting region (401); and also includes a light detection region (501), a contact electrode (102) of the light emitting region, a contact electrode (502) of the light detection region, a bonding electrode (103) of the light emitting region, a bonding electrode (503) of the light detection region, and an isolation layer (600) that isolates the light emitting regions and the light detection regions from each other; the light emitting region and the light detection region have the same resonant cavity (800) and active region (801) structure; The first light emitting region (101), the second light emitting region (201), the third light emitting region (301), and the fourth light emitting region (401) are located at the four corners of the chip, respectively, and the light detection region (501) is located at the center of the chip. Viewed in a vertical cross-section along the diagonal of the chip, it includes an upper Bragg mirror (700), a resonant cavity (800), a lower Bragg mirror (900), a substrate (002), and a lower electrode (001). The upper Bragg mirror (700) is composed of alternating layers of relatively high refractive index material (701) and relatively low refractive index material (702) with a thickness of 1 / 4 of the optical wavelength. The resonant cavity (800) contains an active region (801). The lower Bragg mirror (900) is composed of alternating layers of relatively high refractive index material (901) and relatively low refractive index material (902) with a thickness of 1 / 4 of the optical wavelength. The material selection of the lower Bragg mirror (900) is the same as that of the upper Bragg mirror (700). The substrate (002) is an N-type GaAs substrate. The lower electrode (001) is made of Au / Ge / Ni.

2. The optoelectronic integrated sensor chip for photoplethysmography (PPG) blood pressure measurement according to claim 1, characterized in that: The first light emitting region (101), the second light emitting region (201), the third light emitting region (301), the fourth light emitting region (401) and the light detection region (501) are formed using photolithography.

3. The optoelectronic integrated sensor chip for photoplethysmography (PPG) blood pressure measurement according to claim 1, characterized in that: The insulating layer material is made of SiO2 or Si3N4 insulating material.

4. The method for an optoelectronic integrated sensor chip for photoplethysmography (PPG) blood pressure measurement according to claim 1, characterized in that: The contact electrode (102) of the light emitting region and the contact electrode (502) of the light detecting region are made of Ti / Au.

5. The optoelectronic integrated sensor chip for photoplethysmography (PPG) blood pressure measurement according to claim 1, characterized in that: The upper Bragg reflector (700), the resonant cavity (800), and the lower Bragg reflector (900) form an optical micro-resonant cavity whose cavity size is on the same order of magnitude as the wavelength of the resonant cavity.

6. The optoelectronic integrated sensor chip for photoplethysmography (PPG) blood pressure measurement according to claim 1, characterized in that: When the chip is working, the bonding electrode (103) of the light-emitting region is positively charged relative to the lower electrode (001), and the bonding electrode (503) of the photodetector region is negatively charged relative to the lower electrode (001). The light-emitting region is forward biased to emit directional light, and the photodetector region is reverse biased to realize the photodetector function. Since the light-emitting region and the photodetector region have the same resonant cavity (800) and active region (801) structure, the radiation spectrum of the light-emitting region matches the absorption spectrum of the detector region after the bias voltage is applied.

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