A SPAD coaxial TO device and its manufacturing method

Abstract

The present application discloses a SPAD coaxial TO device and a manufacturing method thereof, and relates to the technical field of coaxial optoelectronic devices. The manufacturing method comprises: after the SPAD is sealed with a cap, it is installed on the device base of a coupling welding platform to obtain the initial light coupling position of the SPAD; under multiple preset alignment bias voltages, the three-dimensional distribution of the photocurrent corresponding to each light coupling position is obtained by line-by-line scanning, thereby obtaining multiple two-dimensional cross-sectional data; based on the multiple two-dimensional cross-sectional data under each alignment bias voltage, an alignment bias voltage that meets the preset conditions is obtained as the initial light coupling condition; under the initial light coupling condition, when the incident light of the pigtail converges at the geometric center of the active area and converges axially in the absorption layer of the SPAD chip, the pigtail and the SPAD device are welded to obtain a SPAD coaxial TO device. The present application can effectively reduce the dark count rate and improve the single photon detection efficiency under the same over-bias voltage.

Description

Technical Field

[0001] The present application relates to the technical field of coaxial optoelectronic devices, and in particular to a SPAD coaxial TO device and a manufacturing method thereof. Background Art

[0002] At present, single-photon avalanche photodiodes (SPADs) are widely used in quantum secure communications, quantum imaging, laser radar, biomedicine, integrated circuit detection and other fields. When the avalanche photodiode APD enters the Geiger mode, that is, the external circuit provides a reverse bias voltage Vr higher than the breakdown voltage Vbr of the device, the instantaneous response current of the device to extremely weak light can reach the mA level, that is, the SPAD has the ability to detect single photons.

[0003] The single-photon detection efficiency (PDE) is an important parameter that characterizes the detection capability of SPADs. Usually, the PDE can be improved by increasing the over-bias voltage applied to both ends of the device. However, under the effects of thermal excitation, inter-band tunneling, and defect-assisted tunneling, the dark counts formed by the self-sustaining avalanche caused by dark carriers also increase with the increase of over-bias voltage. For SPADs, the dark count rate under the premise of meeting a certain PDE is the core indicator of single-photon performance, which determines the degree to which the single-photon avalanche signal can be extracted. Therefore, how to reduce the dark count rate is a key technology to achieve high-performance SPADs. Summary of the invention

[0004] In view of the defects existing in the prior art, the purpose of the present application is to provide a SPAD coaxial TO device and a manufacturing method thereof, so as to solve the problem of high dark count rate in the related art.

[0005] The first aspect of the present application provides a method for manufacturing a SPAD coaxial TO device, which comprises the steps of:

[0006] After the SPAD is capped and welded, it is mounted on the device base of the coupling welding platform to obtain the position and angle of the SPAD when it outputs the peak photocurrent, which is used as the initial coupling position of the SPAD.

[0007] Under multiple preset alignment bias voltages, the three-dimensional distribution of the photogenerated current corresponding to each light coupling position is obtained by line-by-line scanning from the initial light coupling position, and then multiple two-dimensional cross-sectional data along different directions are obtained; in the above two-dimensional cross-sectional data, the abscissa is the light coupling position of the corresponding cross section, and the ordinate is the photogenerated current value;

[0008] Based on multiple two-dimensional cross-sectional data under each alignment bias voltage, an alignment bias voltage that meets preset conditions is obtained as an initial light coupling condition; the preset conditions are: the electric field of the photogenerated current is uniform and has no edge breakdown, and the photogenerated current decrease rate at the edge of the active area is greater than a first rate threshold;

[0009] Under the above initial light coupling conditions, when the incident light of the pigtail converges at the geometric center of the active area and axially converges in the absorption layer of the SPAD chip, the pigtail and the SPAD device are welded and fixed to obtain a SPAD coaxial TO device.

[0010] In some embodiments, when in the two-dimensional cross-sectional data, the absolute values ​​of the differences between two photogenerated currents at positions equidistant from the edges of the active regions on both sides are both less than a first difference threshold, it is determined that the electric field of the photogenerated current is uniform.

[0011] In some embodiments, in the above three-dimensional distribution, the photogenerated current is used as the Z-axis coordinate, the row and column positions of the light coupling positions are used as the X-axis coordinate and the Y-axis coordinate, respectively, and the X-coordinate and the Y-coordinate of the initial light coupling position are both 0;

[0012] Multiple 2D cross-section data along different directions include:

[0013] The two-dimensional cross-sectional data of the cross-sectional area along the X-axis, the two-dimensional cross-sectional data of the cross-sectional area along the Y-axis, the two-dimensional cross-sectional data of the cross-sectional area after the X-axis is rotated 45° clockwise around the Z-axis, and the two-dimensional cross-sectional data of the cross-sectional area after the Y-axis is rotated 45° clockwise around the Z-axis.

[0014] In some embodiments, starting from the initial light coupling position, a three-dimensional distribution of the photogenerated current corresponding to each light coupling position is obtained by scanning line by line, specifically including:

[0015] The light coupling position is adjusted from the origin to the negative direction of the X axis until the photocurrent decays to a preset current value, and this point is taken as the starting point;

[0016] Move from the starting point to the positive direction of the X-axis by the first step length, until the photocurrent decays to the preset current value, move to the positive direction of the Y-axis by the first step length, and then move to the negative direction of the X-axis by the first step length, until the photocurrent decays to the preset current value again, move to the positive direction of the Y-axis by the first step length, and then move to the positive direction of the X-axis by the first step length, until the response test of the positive half of the Y-axis is completed;

[0017] Move the first step from the starting point to the negative direction of the Y axis;

[0018] Move in the positive direction of the X-axis by the first step length until the photocurrent decays to the preset current value, then move in the negative direction of the Y-axis by the first step length, then move in the negative direction of the X-axis by the first step length until the photocurrent decays to the preset current value again, then move in the negative direction of the Y-axis by the first step length, until the response test of the negative half of the Y-axis is completed;

[0019] Each time the first step is moved, the photocurrent at the current coupling position is obtained.

[0020] In some embodiments, when the distances from the initial light coupling position to each light coupling position where the photogenerated current decays to a preset current value are the same, and the absolute value of the difference in attenuation rate per unit distance moved in any two directions is less than a second difference threshold, it is determined that the incident light of the pigtail converges at the geometric center of the active area.

[0021] In some embodiments, when the distances from the initial coupling position to the coupling positions where the photogenerated current decays to a preset current value are different, or the absolute value of the difference in attenuation rate per unit distance moved in any two directions is not less than a second difference threshold, the initial coupling conditions are updated, and the updated initial coupling conditions are used to again determine whether the incident light of the pigtail converges at the geometric center of the active area.

[0022] In some embodiments, when the pigtail moves a second step toward the SPAD, if the decay rate of the photogenerated current is greater than the second rate threshold, the pigtail moves a third step away from the SPAD until the absolute value of the difference between the photogenerated current and the peak photocurrent is less than the third difference threshold, and it is determined that the incident light is axially converged in the absorption layer of the SPAD chip;

[0023] The third step length is smaller than the second step length.

[0024] In some embodiments, if the decay rate of the photogenerated current is less than or equal to the second rate threshold, the second step length is continued to be moved toward the SPAD until the decay rate of the photogenerated current is greater than the second rate threshold.

[0025] In some embodiments, the alignment bias voltage is set according to the breakdown voltage of the SPAD and is smaller than the breakdown voltage.

[0026] A second aspect of the present application provides a SPAD coaxial TO device, which is manufactured by the above-mentioned manufacturing method.

[0027] The beneficial effects of the technical solution provided by this application include:

[0028] The SPAD coaxial TO device and its manufacturing method of the present application, after the SPAD is capped and welded, the initial light coupling position is obtained, and then the alignment bias voltage that meets the preset conditions is obtained as the initial light coupling condition; then, under the initial light coupling condition, when the incident light of the pigtail converges at the geometric center of the active area and axially converges in the absorption layer of the SPAD chip, the pigtail and the SPAD device are welded and fixed to obtain the SPAD coaxial TO device; therefore, not only can the position of photogenerated carrier generation in the active area be accurately controlled to achieve the purpose of controlling the charge persistence effect and effectively reducing the dark count rate, but also the single-photon detection efficiency under the same over-bias voltage can be improved by improving the coupling efficiency; at the same time, the product quality consistency problem introduced by the packaging can be avoided, which helps to improve the device yield. BRIEF DESCRIPTION OF THE DRAWINGS

[0029] In order to more clearly illustrate the technical solutions in the embodiments of the present application, the drawings required for use in the description of the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present application. For ordinary technicians in this field, other drawings can be obtained based on these drawings without creative work.

[0030] Figure 1 This is a first flow chart of the manufacturing method in the embodiment of the present application;

[0031] Figure 2 is a distribution diagram of normalized photogenerated current under different alignment bias voltages in the embodiment of the present application;

[0032] Figure 3 This is a schematic diagram of determining that the focus is outside the device in an embodiment of the present application;

[0033] Figure 4 This is a schematic diagram of determining that the focus is within the device in an embodiment of the present application;

[0034] Figure 5 This is a second flow chart of the production method in the embodiment of the present application. DETAILED DESCRIPTION

[0035] In order to make the purpose, technical solutions and advantages of the present application clearer, the present invention is further described in detail below in conjunction with the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not intended to limit the present invention. In addition, the technical features involved in each embodiment of the present invention described below can be combined with each other as long as they do not conflict with each other.

[0036] The embodiment of the present application provides a method for manufacturing a SPAD coaxial TO device, and particularly relates to an active alignment coupling method for a coaxial optoelectronic device, which can solve the problem of high dark count rate in related technologies.

[0037] like Figure 1 As shown, the method for manufacturing a SPAD coaxial TO device in an embodiment of the present application specifically includes the following steps:

[0038] S1. After the SPAD is capped and welded, it is mounted on the device base of the coupling welding platform to obtain the position and angle of the SPAD when it outputs peak photocurrent, which is used as the initial coupling position of the SPAD to achieve initial coarse alignment.

[0039] In this embodiment, after the SPAD device cap sealing operation is completed, it can be installed as a whole on the coupling welding platform device base to perform peak photocurrent light seeking operation, and the input optical power during the light seeking operation is 10μW. Among them, the relative position of the SPAD and the coupling welding platform is fixed, and the initial coupling position of the SPAD is determined by multi-axis fine-tuning the coupling welding platform.

[0040] S2. Under multiple preset alignment bias voltages, starting from the initial light coupling position, obtain the three-dimensional distribution of the photogenerated current corresponding to each light coupling position by line-by-line scanning, and then obtain multiple two-dimensional cross-sectional data along the cross-section in different directions; in the above two-dimensional cross-sectional data, the horizontal axis is the light coupling position of the corresponding cross section, and the vertical axis is the photogenerated current value.

[0041] In this embodiment, the two-dimensional distribution of the photocurrent corresponding to the light coupling position of 10 μW incident light power is recorded by line-by-line scanning. The horizontal and vertical coordinates of the above two-dimensional distribution of light coupling positions correspond to the relative position coordinates of the light spot in the active area.

[0042] Optionally, the horizontal and vertical coordinates of the coupling position record the relative horizontal position of the corresponding light spot on the tube cap lens and the optical axis (i.e., the overlapping center axis of the lens and the SPAD photosensitive surface), rather than the absolute position of the corresponding light spot in the active area. Therefore, it is necessary to obtain reference information of the actual position of the light spot in the active area through optical simulation.

[0043] S3. Based on multiple two-dimensional cross-sectional data under each alignment bias voltage, an alignment bias voltage that meets preset conditions is obtained as the initial light coupling condition; the above preset conditions are: the electric field of the photogenerated current is uniform and there is no edge breakdown, and the photogenerated current decrease rate at the edge of the active area is greater than the first rate threshold, that is, the photogenerated current is sensitive to changes in the light coupling position.

[0044] In this embodiment, multiple alignment bias voltages may be set as much as possible to test and select the light coupling conditions, and then the test data may be combined and analyzed to find the relatively optimal initial light coupling condition.

[0045] S4. Under the above initial light coupling conditions, when the incident light of the pigtail converges at the geometric center of the active area and axially converges in the absorption layer of the SPAD chip, the pigtail and the SPAD device are welded and fixed to obtain a SPAD coaxial TO device.

[0046] The manufacturing method of this embodiment obtains the initial light coupling position after the SPAD is capped and welded, and then obtains the alignment bias voltage that meets the preset conditions as the initial light coupling condition; then, under the initial light coupling condition, when the incident light of the pigtail converges at the geometric center of the active area and axially converges in the absorption layer of the SPAD chip, the pigtail and the SPAD device are welded and fixed to obtain a SPAD coaxial TO device; therefore, not only can the position of photogenerated carrier generation in the active area be accurately controlled to achieve the purpose of controlling the charge persistence effect and effectively reducing the dark count rate, but also the single-photon detection efficiency under the same over-bias voltage can be improved by improving the coupling efficiency; at the same time, the product quality consistency problem introduced by the packaging can be avoided, which helps to improve the device yield.

[0047] The manufacturing method of this embodiment is based on active alignment, which is also called active optical coupling and is a commonly used alignment technology in the manufacture of SPAD coaxial TO devices. In active optical coupling technology, the optical axis is usually aligned by applying an external bias voltage to put the detector in a working state, that is, the coupling welding machine adjusts and monitors the changes in the SPAD light response in this process through four-dimensional (three-dimensional + rotation angle) micro-adjustments, and records the position and angle when the light response current is maximum. Finally, the adjusted pigtail metal hoop, metal sleeve and tube shell are fixed to each other through puncture welding and lap welding. However, SPAD generally works in Geiger mode, and ordinary coupling welding machines do not have quenching and counting capabilities, and cannot truly realize the active alignment of the SPAD in a working state. Usually, without modifying the hardware of the coupling welding machine, the SPAD is applied with a breakdown voltage below V UV reverse bias voltage for active optical coupling.

[0048] In some embodiments, due to reasons such as the diffusion process, the diffusion morphology of the low-concentration area after two diffusions may not be uniform everywhere, or the edge curvature of the active area may not be ideal. A larger alignment bias voltage that has not been optimized may amplify the uneven electric field distribution in the active area, thereby causing alignment failure.

[0049] When the light coupling spot size is larger than the photosensitive surface size, or when the light coupling error occurs and exceeds a certain tolerance range, in addition to causing a decrease in coupling efficiency, which in turn affects the PDE under the same over-bias, it will also introduce a charge persistence effect, that is, after the photogenerated carriers are generated in the area outside the depletion region in the absorption layer, the longitudinal electric field component in these areas is not strong enough, so the carriers cannot immediately cross the valence band step of the InGaAs / InP material interface. Instead, under the action of the transverse electric field component, they drift laterally for a certain period of time to reach the depletion region and cause an avalanche. Taking the gated quenching mode as an example, this delayed lightless avalanche will greatly increase the probability of triggering miscounts in SPAD applications with a rate above 6.67MHz. Therefore, it is necessary to ensure that the photons are accurately coupled to the center of the active area so that the photon absorption and photogenerated carrier generation positions are precisely controllable.

[0050] On the basis of the above embodiment, in this embodiment, when the absolute value of the difference between two photocurrents at positions equidistant from the edges of the active regions on both sides in the two-dimensional cross-sectional data is less than the first difference threshold, the photocurrent electric field is judged to be uniform. Optionally, the first difference threshold is 5%. When the absolute value of the difference between two photocurrents at positions equidistant from the edges of the active regions on both sides is greater than 5%, there will be a large deviation between the position found by the automatic peak search and the actual geometric center position, and the photocurrent electric field is judged to be non-uniform.

[0051] In this embodiment, when a two-dimensional cross-sectional data is calculated from the light coupling position 0 to both sides, if the decrease rate of two adjacent photogenerated current values ​​is not less than a preset value, the position far away from the light coupling position 0 is determined to be the edge of the active area.

[0052] Optionally, the preset value is 20%, which is determined by the APD detection sensitivity and the source meter accuracy.

[0053] In this embodiment, the first rate threshold is 2.5 μA / μm, that is, the decreasing rate of the photo-generated current at the edge of the active region must be greater than 2.5 μA / μm.

[0054] At this time, since the decrease rate of the photocurrent value at the edge of the active area must be no less than 20%, that is, the relative decrease rate must be no less than 10% / μm, and the absolute value of the decrease rate must be greater than 2.5μA / μm, it means that the photocurrent in the central area of ​​the active area must reach at least 25μA, in order to eliminate the misjudgment caused by the source meter measurement error.

[0055] On the basis of the above embodiment, in this embodiment, in the above three-dimensional distribution, the photogenerated current is used as the Z-axis coordinate, the row and column positions of the light coupling position are used as the X-axis coordinate and the Y-axis coordinate respectively, and the X-coordinate and Y-coordinate of the initial light coupling position are both 0.

[0056] Preferably, the above-mentioned multiple two-dimensional cross-sectional data along different directional planes are all vertical planes passing through the Z axis. Among them, the multiple two-dimensional cross-sectional data are provided with four, including: two-dimensional cross-sectional data along the direction of the plane where the X axis is located, two-dimensional cross-sectional data along the direction of the plane where the Y axis is located, two-dimensional cross-sectional data after the X axis is rotated 45° clockwise around the Z axis, and two-dimensional cross-sectional data after the Y axis is rotated 45° clockwise around the Z axis.

[0057] Among them, the two-dimensional cross-sectional data of the surface cross-section along the direction of the X-axis, that is, the Y coordinate of the coupling position is 0; the two-dimensional cross-sectional data of the surface cross-section along the direction of the Y-axis, that is, the X coordinate of the coupling position is 0.

[0058] Furthermore, starting from the initial light coupling position, a three-dimensional distribution of the photogenerated current corresponding to each light coupling position is obtained by a line-by-line scanning method, which specifically includes the following steps:

[0059] First, the light coupling position is adjusted from the origin to the negative direction of the X-axis until the photocurrent decays to a preset current value, and this point is taken as the starting point;

[0060] Secondly, move from the starting point to the positive direction of the X-axis with the first step length, until the photogenerated current decays to the preset current value, move to the positive direction of the Y-axis with the first step length, and then move to the negative direction of the X-axis with the first step length, until the photogenerated current decays to the preset current value again, move to the positive direction of the Y-axis with the first step length, and then move to the positive direction of the X-axis with the first step length, until the response test of the positive half of the Y-axis is completed.

[0061] Then, move the first step from the starting point in the negative direction of the Y axis.

[0062] Finally, move in the positive direction of the X-axis with the first step length until the photogenerated current decays to the preset current value, then move in the negative direction of the Y-axis with the first step length, then move in the negative direction of the X-axis with the first step length, until the photogenerated current decays to the preset current value again, then move in the negative direction of the Y-axis with the first step length, then move in the positive direction of the X-axis with the first step length, until the response test of the negative half of the Y-axis is completed.

[0063] In this embodiment, each time the first step is moved, the photogenerated current at the current light coupling position is obtained, and then the three-dimensional distribution of the photogenerated current corresponding to each light coupling position can be obtained.

[0064] In this embodiment, taking the first step length of 2 μm and the preset current value of 10 μA as an example, obtaining the three-dimensional distribution of the photogenerated current corresponding to each light coupling position specifically includes:

[0065] a. Manually adjust the light coupling position toward the negative direction of the X axis until the photocurrent decays to 10μA and stops, and take this point as the starting point;

[0066] b. Move from the starting point to the positive direction of the X axis in steps of 2 μm, and record the photogenerated current at each stop point until the photogenerated current decays to 10 μA again;

[0067] c. After moving 2μm in the positive direction of the Y axis, move in the negative direction of the X axis in steps of 2μm, and record the photogenerated current at each stop point until the photogenerated current decays to 10μA again;

[0068] d. After moving 2 μm in the positive direction of the Y axis, move in the positive direction of the X axis in steps of 2 μm, and record the photogenerated current at each stop point until the photogenerated current decays to 10 μA again;

[0069] e. Repeat steps c and d until the response test of the positive half of the Y axis is completed;

[0070] f. Return to the starting point;

[0071] g. After moving 2 μm in the negative direction of the Y axis, move in the positive direction of the X axis in steps of 2 μm, and record the photogenerated current at each stop point until the photogenerated current decays to 10 μA again;

[0072] h. After moving 2 μm in the negative direction of the Y axis, move in the negative direction of the X axis in steps of 2 μm, and record the photogenerated current at each stop point until the photogenerated current decays to 10 μA again;

[0073] i. Repeat steps g and h until the response test of the negative half of the Y axis is completed.

[0074] Alternatively, if a dwell point exactly around 10 μA (±0.5 μA) cannot be found or both sides cannot be found at the same time, consider reducing the step size to 1 μm.

[0075] In this embodiment, the alignment bias voltage is set according to the breakdown voltage of the SPAD and is less than the breakdown voltage. UV alignment bias voltage, and multiple alignment bias voltages that are smaller than the breakdown voltage.

[0076] Specifically, the breakdown voltage of the SPAD in this embodiment is about 80V, so four groups of V UV The voltages are 7V, 5V, 3V, 2V, and 60V, 65V, and 70V which are even lower than the breakdown voltage, for a total of 7 groups.

[0077] In this embodiment, the three-dimensional distribution of the photogenerated current corresponding to the coupling position is compared with the distribution of the normalized photogenerated current under different alignment bias voltages in the two-dimensional cross-sectional data obtained along the cross-sectional surface in the direction of the Y axis. Figure 2 shown.

[0078] When the bias voltage is not higher than 70V, the photocurrent changes more slowly near the vertex, and in the center of the active area, some photocurrents are less than 25μA. Therefore, it is difficult to eliminate the misjudgment caused by the source meter measurement error when the bias voltage is not higher than 70V. UV =3V or 2V, the bias voltage is high and too close to the breakdown voltage, and the curve has a certain degree of asymmetry. Therefore, if the SPAD itself has edge breakdown, it is easy to make a misjudgment in the coupling mode of automatically searching for the electric field peak using this condition.

[0079] In summary, V UV =5V or 7V is used as the initial condition to complete the subsequent sample alignment operation.

[0080] Based on the above embodiments, in this embodiment, when the distances from the initial coupling position to the coupling positions where the photogenerated current decays to a preset current value are the same, and the absolute value of the difference in attenuation rate per unit distance moved in any two directions is less than a second difference threshold, it is determined that the incident light of the pigtail converges at the geometric center of the active area.

[0081] Furthermore, when the distances from the initial coupling position to the coupling positions where the photogenerated current decays to a preset current value are different, or the absolute value of the difference in attenuation rate per unit distance moved in any two directions is not less than a second difference threshold, the initial coupling conditions are updated, and the updated initial coupling conditions are used to again determine whether the incident light of the pigtail converges at the geometric center of the active area.

[0082] Preferably, the alignment bias voltage corresponding to the initial light coupling condition is reduced by 2V, which can be used as the updated initial light coupling condition to again determine whether the incident light converges at the geometric center of the active area.

[0083] Based on the above embodiment, in this embodiment, when the pigtail moves the second step length toward the SPAD, if the decay rate of the photogenerated current is greater than the second rate threshold, it moves away from the SPAD with a third step length until the absolute value of the difference between the photogenerated current and the peak photocurrent is less than the third difference threshold, and it is determined that the incident light is axially converged in the absorption layer of the SPAD chip. The third step length is smaller than the second step length.

[0084] Furthermore, when the pigtail moves a second step toward the SPAD, if the decay rate of the photogenerated current is less than or equal to the second rate threshold, it continues to move a second step toward the SPAD until the decay rate of the photogenerated current is greater than the second rate threshold.

[0085] In this embodiment, the coupling welding machine is controlled by writing a script so that the coupling welding platform can automatically complete the adjustment in the axial and horizontal directions.

[0086] In this embodiment, the breakdown voltage is 80V, and the breakdown voltage is below V UV =5V is taken as an example as the initial light coupling condition, that is, the alignment bias voltage corresponding to the initial light coupling condition is 75V. Then, with the initial light coupling position as the origin, a radial scanning method is used to determine whether the incident light converges at the geometric center of the active area.

[0087] Specifically, the script automatically moves the preset distances (step 0.5 μm) along the positive direction of the X-axis, the negative direction of the X-axis, the positive direction of the Y-axis, and the negative direction of the Y-axis to confirm the geometric symmetry of the response, that is, when the geometric center to the photocurrent decays to 10 μA, the distances of each point should be equal, and the attenuation rate of the moving unit distance is equivalent in each direction (that is, the absolute value of the difference in attenuation rate is not less than the second difference threshold), and it is determined that the incident light of the pigtail converges at the geometric center of the active area. Among them, the preset distance can be designed with reference to the radius of the photosensitive surface. In this embodiment, the preset distance is 8 μm.

[0088] If the result does not match, it means that under the initial light coupling condition, the incident light of the pigtail does not converge at the geometric center of the active area. At this time, the alignment bias voltage corresponding to the initial light coupling condition can be reduced by 2V, and then this step can be repeated until the judgment condition is met.

[0089] Among them, since the position of the pigtail is fixed, the script is based on controlling the movement of the coupling welding platform to achieve the movement of the coupling position.

[0090] Taking the second step length of 0.8μm and the third step length of 0.4μm as examples, the vertical direction of the pigtail close to the SPAD is the negative direction of the Z axis, and the vertical direction of the pigtail away from the SPAD is the positive direction of the Z axis. After determining that the incident light of the pigtail converges at the geometric center of the active area, the pigtail needs to be moved along the negative direction of the Z axis in steps of 0.8μm, that is, gradually approaching the SPAD. If the photocurrent does not have an obvious monotonic decrease, that is, the attenuation rate of the photocurrent is less than or equal to the second rate threshold, then Figure 3 As shown in FIG. 1 , it is determined that the focus is outside the device, and the object distance (i.e., the distance between the pigtail end face and the lens) needs to be further shortened; when the photocurrent begins to decrease monotonically, that is, the attenuation rate of the photocurrent is greater than the second rate threshold, as shown in FIG. Figure 4 As shown, it is determined that the focus has entered the device and part of the light has been blocked by the aperture. At this time, the pigtail is moved along the positive direction of the Z axis in steps of 0.4μm, that is, gradually away from the SPAD, until the photogenerated current is found to return to the maximum value near the peak photocurrent, that is, the absolute value of the difference between the current photogenerated current and the peak photocurrent is less than the third difference threshold. At this time, it is determined that the incident light is axially converged in the absorption layer of the SPAD chip, and the spot diameter is minimized.

[0091] like Figure 5 As shown, the manufacturing method of this embodiment specifically includes:

[0092] A1. After the SPAD cap is sealed, it is installed on the device base of the coupling welding platform;

[0093] A2. Initialize the XYZ-T four-dimensional coarse alignment and determine the initial coupling position;

[0094] A3. Obtain the three-dimensional distribution of the photocurrent corresponding to the light coupling position under multiple sets of alignment bias voltages, and then obtain multiple two-dimensional cross-sectional data along different directions;

[0095] A4. Based on multiple two-dimensional cross-sectional data under each alignment bias voltage, an alignment bias voltage satisfying a preset condition is obtained as an initial light coupling condition;

[0096] A5. The script controls the automatic optimization alignment of the XY plane to determine whether the incident light converges at the geometric center of the active area. If so, turn to A7; otherwise, turn to A6;

[0097] A6. Update the initial coupling conditions and go to A5.

[0098] A7. The script controls the automatic optimization alignment of the Z center axis to determine whether the incident light is axially focused in the absorption layer of the SPAD chip. If so, turn to A9; otherwise, turn to A8;

[0099] A8. Adjust the distance between the fiber pigtail end face and the lens, and turn to A7.

[0100] A9. After penetration welding and two-dimensional confirmation of alignment by radial scanning, lap welding is performed.

[0101] In this embodiment, for SPAD devices from the same batch, coupling can be performed directly using the initial coupling condition of 75V found above, and a radial scanning method can be used to find the geometric center position of the active area at the initial coupling position of the device. When it is determined that the light spot converges axially in the absorption layer of the SPAD chip, the pigtail and the SPAD device are puncture welded and aligned again in two dimensions using a radial scanning method, and then overlap welded to obtain a SPAD coaxial TO device.

[0102] The present application also provides an embodiment of a SPAD coaxial TO device, and the SPAD coaxial TO device is manufactured by the above-mentioned manufacturing method.

[0103] The SPAD coaxial TO device of this embodiment is suitable for the above-mentioned manufacturing methods, and can ensure the realization of the optical path in the device: ① the incident light in the horizontal direction converges at the geometric center of the active area; ② the incident light in the axial direction converges in the absorption layer of the SPAD chip (that is, the spot diameter is the smallest); so as to effectively reduce the dark counts caused by the lightless delay avalanche caused by the generation position of photogenerated carriers at the periphery of the active area, thereby improving the performance of SPAD in related applications.

[0104] In the description of the present application, it should be noted that the terms "upper", "lower", etc. indicate orientations or positional relationships based on the orientations or positional relationships shown in the accompanying drawings, and are only for the convenience of describing the present application and simplifying the description, rather than indicating or implying that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation, and therefore cannot be understood as a limitation on the present application. Unless otherwise clearly specified and limited, the terms "installed", "connected", and "connected" should be understood in a broad sense, for example, it can be a fixed connection, a detachable connection, or an integral connection; it can be a mechanical connection or an electrical connection; it can be a direct connection, or it can be an indirect connection through an intermediate medium, or it can be a connection between the two elements. For those of ordinary skill in the art, the specific meanings of the above terms in the present application can be understood according to the specific circumstances.

[0105] It should be noted that, in this application, relational terms such as "first" and "second" are only used to distinguish one entity or operation from another entity or operation, and do not necessarily require or imply any such actual relationship or order between these entities or operations. Moreover, the terms "include", "comprise" or any other variants thereof are intended to cover non-exclusive inclusion, so that a process, method, article or device including a series of elements includes not only those elements, but also other elements not explicitly listed, or also includes elements inherent to such process, method, article or device. In the absence of further restrictions, the elements defined by the sentence "comprise a ..." do not exclude the presence of other identical elements in the process, method, article or device including the elements.

[0106] The above description is only a specific implementation of the present application, so that those skilled in the art can understand or implement the present application. Various modifications to these embodiments will be apparent to those skilled in the art, and the general principles defined herein can be implemented in other embodiments without departing from the spirit or scope of the present application. Therefore, the present application will not be limited to the embodiments shown herein, but will conform to the widest range consistent with the principles and novel features applied for herein.

Claims

1. A method for manufacturing a SPAD coaxial TO device, characterized in that: It includes the steps of: After the SPAD is capped and welded, it is mounted on the device base of the coupling welding platform to obtain the position and angle of the SPAD when it outputs the peak photocurrent, which is used as the initial coupling position of the SPAD. Under multiple preset alignment bias voltages, starting from the initial light coupling position, a three-dimensional distribution of the photogenerated current corresponding to each light coupling position is obtained by line-by-line scanning, thereby obtaining multiple two-dimensional cross-sectional data along different directions; in the two-dimensional cross-sectional data, the abscissa is the light coupling position of the corresponding cross section, and the ordinate is the photogenerated current value; Based on a plurality of two-dimensional cross-sectional data under each alignment bias voltage, an alignment bias voltage satisfying a preset condition is obtained as an initial light coupling condition; The preset conditions are: the electric field of the photogenerated current is uniform and has no edge breakdown, and the rate at which the photogenerated current decreases at the edge of the active region is greater than a first rate threshold; Under the initial light coupling conditions, when the incident light of the pigtail converges at the geometric center of the active area and axially converges in the absorption layer of the SPAD chip, the pigtail and the SPAD device are welded and fixed to obtain a SPAD coaxial TO device.

2. The method for manufacturing a SPAD coaxial TO device according to claim 1, characterized in that: When the absolute values ​​of the differences between two photogenerated currents at positions equidistant from the edges of the active regions on both sides in the two-dimensional cross-sectional data are both less than a first difference threshold, it is determined that the electric field of the photogenerated current is uniform.

3. The method for manufacturing a SPAD coaxial TO device according to claim 1, characterized in that: In the three-dimensional distribution, the photogenerated current is used as the Z-axis coordinate, the row and column positions of the light coupling positions are used as the X-axis coordinate and the Y-axis coordinate, respectively, and the X-coordinate and the Y-coordinate of the initial light coupling position are both 0; Multiple 2D cross-section data along different directions include: The two-dimensional cross-sectional data of the cross-sectional area along the X-axis, the two-dimensional cross-sectional data of the cross-sectional area along the Y-axis, the two-dimensional cross-sectional data of the cross-sectional area after the X-axis is rotated 45° clockwise around the Z-axis, and the two-dimensional cross-sectional data of the cross-sectional area after the Y-axis is rotated 45° clockwise around the Z-axis.

4. The method for manufacturing a SPAD coaxial TO device according to claim 3, characterized in that: From the initial light coupling position, the three-dimensional distribution of the photogenerated current corresponding to each light coupling position is obtained by line-by-line scanning, specifically including: The light coupling position is adjusted from the origin to the negative direction of the X axis until the photocurrent decays to a preset current value, and this point is taken as the starting point; Move from the starting point to the positive direction of the X-axis by the first step length, until the photocurrent decays to the preset current value, move to the positive direction of the Y-axis by the first step length, and then move to the negative direction of the X-axis by the first step length, until the photocurrent decays to the preset current value again, move to the positive direction of the Y-axis by the first step length, and then move to the positive direction of the X-axis by the first step length, until the response test of the positive half of the Y-axis is completed; Move the first step from the starting point to the negative direction of the Y axis; Move in the positive direction of the X-axis by the first step length until the photocurrent decays to the preset current value, then move in the negative direction of the Y-axis by the first step length, then move in the negative direction of the X-axis by the first step length until the photocurrent decays to the preset current value again, then move in the negative direction of the Y-axis by the first step length, until the response test of the negative half of the Y-axis is completed; Each time the first step is moved, the photocurrent at the current coupling position is obtained.

5. The method for manufacturing a SPAD coaxial TO device according to claim 1, characterized in that: When the distances from the initial coupling position to the coupling positions where the photogenerated current decays to a preset current value are the same, and the absolute value of the difference in attenuation rate per unit distance moved in any two directions is less than a second difference threshold, it is determined that the incident light of the pigtail converges at the geometric center of the active area.

6. The method for manufacturing a SPAD coaxial TO device according to claim 5, characterized in that: When the distances from the initial coupling position to the coupling positions where the photogenerated current decays to a preset current value are different, or the absolute value of the difference in attenuation rate per unit distance moved in any two directions is not less than a second difference threshold, the initial coupling conditions are updated, and the updated initial coupling conditions are used to determine again whether the incident light of the pigtail converges at the geometric center of the active area.

7. The method for manufacturing a SPAD coaxial TO device according to claim 1, characterized in that: When the pigtail moves the second step length toward the SPAD, if the decay rate of the photogenerated current is greater than the second rate threshold, it moves the third step length toward the SPAD away from the SPAD until the absolute value of the difference between the photogenerated current and the peak photocurrent is less than the third difference threshold, and it is determined that the incident light is axially converged in the absorption layer of the SPAD chip; The third step length is smaller than the second step length.

8. The method for manufacturing a SPAD coaxial TO device according to claim 7, characterized in that: If the decay rate of the photogenerated current is less than or equal to the second rate threshold, continue to move the second step length toward the SPAD until the decay rate of the photogenerated current is greater than the second rate threshold.

9. The method for manufacturing a SPAD coaxial TO device according to claim 1, characterized in that: The alignment bias voltage is set according to a breakdown voltage of the SPAD and is smaller than the breakdown voltage.

10. A SPAD coaxial TO device, characterized in that: The invention is prepared by the preparation method described in any one of claims 1 to 9.

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