Method for suppressing degradation of semiconductor devices that emit electromagnetic waves

Abstract

To suppress degradation of semiconductor elements emitting electromagnetic waves.SOLUTION: A method for suppressing degradation of a semiconductor element emitting electromagnetic waves has a first process for applying a voltage of a first waveform to the semiconductor element, and after the first process, a second process for applying a voltage of a second waveform different from the first waveform to the semiconductor element.SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] The present invention relates to a method for suppressing deterioration of a semiconductor element that emits electromagnetic waves.

Background Art

[0002] Devices that use semiconductor elements that emit electromagnetic waves (for example, ultraviolet rays) to sterilize (also referred to as inactivate) bacteria, viruses, etc. have been proposed (for example, see Patent Document 1).

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] It is desired to suppress deterioration of a semiconductor element that emits electromagnetic waves.

Means for Solving the Problems

[0005] The method for suppressing deterioration of a semiconductor element that emits electromagnetic waves in the present embodiment includes a first step of applying a voltage of a first waveform to the semiconductor element, and a second step of applying a voltage of a second waveform different from the first waveform to the semiconductor element after the first step.

Effects of the Invention

[0006] According to the present invention, deterioration of a semiconductor element that emits ultraviolet rays can be suppressed.

Brief Description of the Drawings

[0007] [Figure 1] FIG. 1 is a first block diagram for explaining the functions of a deterioration suppression system. [Figure 2] FIG. 2 is a first waveform diagram of the voltage applied to a UVLED. [Figure 3] Figure 3 shows the second waveform of the voltage applied to the UV LED. [Figure 4] Figure 4 is a flowchart illustrating the flow of the degradation suppression process. [Figure 5] Figure 5 is a graph showing the change in dose rate of a UV LED after degradation suppression according to this embodiment. [Figure 6] Figure 6 is a graph showing the change in dose rate of the UV LED when the voltage of the comparative example was applied. [Figure 7] Figure 7 is a second block diagram illustrating the function of the degradation suppression system. [Figure 8] Figure 8 is a schematic cross-sectional view illustrating a first sterilization apparatus having a UV LED on which the degradation suppression process of this embodiment has been performed. [Figure 9] Figure 9 is a schematic cross-sectional view illustrating a second sterilization apparatus having a UV LED on which the degradation suppression process of this embodiment has been performed. [Modes for carrying out the invention]

[0008] (First Embodiment) Figure 1 is a first block diagram illustrating the function of a degradation suppression system that suppresses the degradation of semiconductor elements that emit electromagnetic waves. The semiconductor elements that emit electromagnetic waves are, for example, semiconductor elements that emit light in the wavelength range between 100 nm and 400 nm (hereinafter referred to as ultraviolet light as appropriate) (Ultraviolet-Light Emitting Diode, UV-LED).

[0009] The degradation suppression system 1 performs a process on the UV LED 200 to suppress its degradation. This degradation suppression makes it possible to extend the lifespan of the UV LED 200.

[0010] The UVLED200 is a semiconductor element that emits ultraviolet light, for example, an aluminum gallium nitride (AlGaN) deep ultraviolet LED, and preferably emits deep ultraviolet light with a wavelength of 220 nm to 350 nm. A voltage is applied to the anode of the UVLED200 from the degradation suppression device 100. The cathode of the UVLED200 is connected to so-called ground. Note that the expression "applying voltage to the anode of the UVLED200" will be appropriately abbreviated as "applying voltage to the UVLED200".

[0011] The degradation suppression device 100 suppresses the degradation of the UV LED 200 by switching the waveform of the voltage applied to the UV LED 200. Specifically, the degradation suppression device 100 performs a UV LED degradation suppression method comprising a first step of applying a voltage of a first waveform to the UV LED 200, and a second step of applying a voltage of a second waveform different from the first waveform to the UV LED 200 after the first step. The reason why degradation suppression is achieved will be explained with reference to Figure 5. Next, the degradation suppression system 1 will be described in detail.

[0012] In the first step, applying a voltage of a first waveform to the UVLED200 reduces the intensity of ultraviolet light emitted by the UVLED200. In the second step, applying a voltage of a second waveform to the UVLED200 increases the intensity of ultraviolet light emitted by the UVLED200.

[0013] Here, the voltage of the first waveform is equal to or greater than the rated voltage of the semiconductor element that emits ultraviolet light. The voltage of the second waveform is equal to or less than the rated voltage of this semiconductor element. The rated voltage of a semiconductor element is a voltage predetermined for each semiconductor element and can be determined from a specification sheet (also called a spec sheet or data sheet).

[0014] Furthermore, the voltage of the first waveform is the voltage of a current greater than or equal to the rated current of the semiconductor element emitting ultraviolet light. The voltage of the second waveform is the voltage of a current less than the rated current of this semiconductor element. Here, the rated current of a semiconductor element is a current predetermined for each semiconductor element and can be specified from a specification sheet or similar document.

[0015] Also, the voltage of the first waveform is, for example, a voltage subjected to Pulse Width Modulation (PWM). The voltage of the second waveform is a constant voltage (also referred to as a DC voltage or a CW voltage).

[0016] Also, the degradation suppression device 100 controls the power supplied to the UV LED 200 to be constant in at least one of the first step and the second step.

[0017] The degradation suppression device 100 includes a control unit 110 and a voltage application unit 120. The control unit 110 is an electronic circuit that controls the voltage application unit 120. The voltage application unit 120 is an electronic circuit that receives the supply of power from the power source PW1 and applies a voltage to the UV LED 200. For example, the control unit 110 controls the voltage application unit 120 and controls the process of switching the voltage applied to the UV LED 200. Hereinafter, this voltage switching will be described with reference to FIGS. 2 and 3.

[0018] FIG. 2 is a first waveform diagram of the voltage applied to the UV LED 200. The horizontal axis represents time, and the vertical axis represents the voltage applied to the UV LED 200. Hereinafter, a voltage higher than the rated voltage of the UV LED 200 will be appropriately referred to as an overrated voltage. Also, a voltage of a current higher than the rated current of the UV LED 200 will be appropriately referred to as an overrated voltage. Also, a voltage lower than the rated voltage of the UV LED 200 will be appropriately referred to as a rated voltage. Also, a voltage of a current lower than the rated current of the UV LED 200 will be appropriately referred to as a rated voltage. Reference numeral Vr in FIG. 2 is the rated voltage of the UV LED 200 or the voltage of the rated current of the UV LED 200.

[0019] The voltage application unit 120 applies an overrated voltage to the UV LED 200 during the first period T1. Then, when the first period T1 elapses, the degradation suppression device 100 switches the voltage applied to the UV LED 200 from the overrated voltage to the rated voltage and applies the rated voltage during the second period T2.

[0020] Figure 3 shows the second waveform of the voltage applied to the UVLED200. The horizontal axis represents time, and the vertical axis represents the voltage applied to the UVLED200. In Figure 3, the voltage of the first waveform is appropriately labeled as PWM voltage, and the voltage of the second waveform is appropriately labeled as DC voltage.

[0021] The voltage application unit 120 applies a PWM voltage to the UV LED 200 during the first period T1, and after the first period T1, the voltage application unit 120 switches the voltage applied to the UV LED 200 and applies a DC voltage during the second period T2.

[0022] When pulse width modulation is applied, the pulse width of the PWM voltage is, for example, 10 μs, and the duty cycle is, for example, 50%. The average current value of the PWM voltage and DC voltage is 700 mA.

[0023] Furthermore, as shown in Figures 2 and 3, the voltage application unit 120 controls the power supplied to the UV LED 200 to a constant level during the first period T1 and the second period T2. By performing the degradation suppression process of this embodiment, even if a constant power is continuously supplied to the UV LED 200, a decrease in intensity can be suppressed.

[0024] At least one of the first period T1 and the second period T2 may be a fixed duration. Alternatively, the first period T1 may be a period corresponding to the characteristics of the semiconductor device emitting ultraviolet light, such as when the intensity of ultraviolet light has decreased by a predetermined rate (e.g., 20%) from the intensity at the start of the first period T1.

[0025] In this embodiment, the first period T1 is exemplified as 70 hours, and the second period T2 is exemplified as 100 hours.

[0026] Alternatively, the control unit 110 may automatically control the voltage application unit 120 to automatically control the voltage switching, or the control unit 110 may be omitted, and this switching may be performed manually.

[0027] Figure 4 is a flowchart illustrating the flow of the degradation suppression process. The timing of the degradation suppression process can vary; it may be performed after the UVLED200 is manufactured but before shipment, or it may be performed after the UVLED200 has been incorporated into a product (e.g., a sterilization device).

[0028] Step S1: The control unit 110 instructs the voltage application unit 120 to start degradation suppression. In response to the start instruction, the voltage application unit 120 applies a voltage of a first waveform to the UVLED 200. For example, the voltage application unit 120 generates a PWM voltage and applies the generated PWM voltage to the UVLED 200.

[0029] Step S2: The control unit 110 determines whether the first period T1 has elapsed. If the control unit 110 determines that the first period T1 has elapsed (Step S2 / YES), it proceeds to Step S3. If the control unit 110 determines that the first period T1 has not elapsed (Step S2 / NO), it continues the time-dependent determination in Step S2. As long as the first period T1 has not elapsed, the voltage application unit 120 continues to apply the PWM voltage to the UVLED 200.

[0030] Step S3: The control unit 110 instructs the voltage application unit 120 to apply the voltage of the second waveform. In response to the application instruction from the control unit 110, the voltage application unit 120 stops applying the voltage of the first waveform to the UVLED200 and applies the voltage of the second waveform to the UVLED200. For example, in response to the application instruction from the control unit 110, the voltage application unit 120 stops applying the PWM voltage to the UVLED200 and applies a DC voltage to the UVLED200.

[0031] Step S4: The control unit 110 determines whether the second period T2 has elapsed. If the control unit 110 determines that the second period T2 has elapsed (Step S4 / YES), it stops applying the DC voltage to the UV LED 200 and terminates the degradation suppression. Alternatively, the application of the DC voltage to the UV LED 200 may be continued without performing this stop.

[0032] If the control unit 110 determines that the second period T2 has not elapsed (step S4 / NO), it continues the time-dependent determination in step S4. While the second period T2 has not elapsed, the voltage application unit 120 continues to apply the DC voltage to the UV LED 200.

[0033] Referring to Figures 5 and 6, the effects resulting from the execution of the degradation suppression process of this embodiment will be explained. In the following explanation, when describing changes in ultraviolet intensity, the ultraviolet dose rate will be used as an example. In Figures 5 and 6, the horizontal axis represents time, and the vertical axis represents the dose rate. The dose rate is in arbitrary units. When showing ultraviolet irradiance on the vertical axis as another example to explain changes in ultraviolet intensity, the unit of irradiance is "mW / cm". 2 "

[0034] Figure 5 is a graph showing the change in dose rate of a UV LED in which degradation suppression was performed according to this embodiment. Figure 6 is a graph showing the change in dose rate of a UV LED in which voltage was applied according to the comparative example. Here, when measuring the dose rate of the UV LED, the distance between the UV LED and the measuring equipment is kept constant throughout the measurement period.

[0035] The graph line L1 in Figures 5 and 6 shows the change in the dose rate of ultraviolet light emitted by the UV LED 200 when the degradation suppression process in this embodiment is performed, for example, as shown in Figure 3. Hereinafter, the dose rate of ultraviolet light emitted by the UV LED will be simply abbreviated as dose rate.

[0036] The graph line L2 in Figure 6 shows the change in dose rate when only a DC voltage is applied to the comparison UV LED, and the graph line L3 in Figure 6 shows the change in dose rate when only a PWM voltage is applied to the comparison UV LED. To facilitate comparison between this embodiment and the comparative example, the graph line L1 from Figure 5 is also shown in Figure 6. Here, the comparison UV LED is the same UV LED as UVLED200.

[0037] First, let's explain the change in ultraviolet dose rate with reference to Figure 5. During the first period T1, from the start of the degradation suppression process (in other words, from the start of applying the PWM voltage), the voltage application unit 120 applies a PWM voltage to the UV LED 200. Here, the first period T1 is 70 hours. The pulse width and duty cycle of this PWM voltage are, for example, 10 μs and 50%, respectively, as explained in Figure 3. The average current value of the PWM voltage is 700 mA. In the first period T1, if the dose rate at the start of applying the PWM voltage is 100, the dose rate at the end of applying the PWM voltage is 84.5. That is, in the first step of applying a voltage of the first waveform (for example, a PWM voltage) to the UV LED 200, the dose rate decreases when the voltage application unit 120 applies the voltage of the first waveform to the UV LED 200. During the first period T1, the rate of decrease in the dose rate per unit time is 22.1% (((100-84.5) / (70 hours))%). Here, the rate of decrease in the dose rate per unit time is the value obtained by expressing the decrease in the dose rate per hour as a percentage.

[0038] Once the first period T1 has elapsed, the voltage application unit 120 stops applying the PWM voltage and applies a DC voltage to the UVLED 200. The average current value of this DC voltage is 700mA, as explained in Figure 3.

[0039] The dose rate at the start of the second period T2 is 84.5, and the dose rate at the end of the second period T2 is 96.5. Here, the second period T2 is 100 hours. That is, in the second step of applying a second waveform voltage (for example, a DC voltage) to the UVLED 200, the dose rate increases as the voltage application unit 120 applies the second waveform voltage to the UVLED 200. The rate of increase in the dose rate per unit time during the second period T2 is 12.0% (((96.5-84.5) / (100 hours))%). Here, the rate of increase in the dose rate per unit time is the value expressed as a percentage of the increase in the dose rate per hour.

[0040] Here, even after the second period T2 has elapsed, the voltage application unit 120 continues to apply a DC voltage to the UVLED 200. The dose rate after the second period T2 has elapsed will be explained. The dose rate at 2000 hours after the start of dose rate measurement is 96. Thus, the rate of decrease in the dose rate in the second step of applying a second waveform voltage (for example, DC voltage) to the UVLED 200 is 0.026% (((96.5-96) / (2000-70 hours))%).

[0041] Thus, in the second step of applying a second waveform voltage (e.g., DC voltage) to the UVLED200, the dose rate decreases after the dose rate increases during the second period T2 by continuing to apply the second waveform voltage. However, the rate of decrease in the dose rate in the second step is smaller than the rate of decrease in the dose rate in the first step of applying a first waveform voltage (e.g., PWM voltage) to the UVLED200 (22.1% in the example in Figure 5).

[0042] As explained above, a constant power supply continues to the UVLED200 during the first period T1, the second period T2, and even after the second period T2, but the dose rate decrease is low at 0.2% ((100-96) / (2000 hours)%).

[0043] Next, referring to graph line L2 in Figure 6, we will explain the change in dose rate when only a DC voltage is applied to the comparison UV LED, and then referring to graph line L3 in Figure 6, we will explain the change in dose rate when only a PWM voltage is applied to the comparison UV LED.

[0044] The average current value of the DC voltage in Figure 6 is 700mA, the same as the average current value when the DC voltage is applied as described in Figure 5. The pulse width and duty cycle of the PWM voltage in Figure 6 are also the same as those when the PWM voltage is applied as described in Figure 5, for example, 10μs and 50%, respectively. The average current value of the PWM voltage is 700mA. The comparison UV LED is also continuously supplied with the same power as the constant power described in Figure 5.

[0045] As shown by graph line L2, if the dose rate at the start of applying only DC voltage is set to 100, the dose rate at the end of the first period T1 (70 hours) is 84.5. After the end of the first period T1, if only DC voltage is applied to the comparison UV LED, the dose rate at 2000 hours after the start of dose rate measurement is 75. Also, as shown by graph line L3, if the dose rate at the start of applying only PWM voltage is set to 100, the dose rate at the end of the first period T1 (70 hours) is 84.5. After the end of the first period T1, if only PWM voltage is applied to the comparison UV LED, the dose rate at 2000 hours after the start of dose rate measurement is 67.5.

[0046] As explained in Figure 5, if the degradation suppression process of this embodiment is performed on the UVLED200, the dose rate will only decrease by about 4 even after 2000 hours have elapsed since the start of measurement (the dose rate reduction rate is 0.2%).

[0047] On the other hand, as explained in Figure 6, when only a DC voltage is applied to the comparison UV LED, the dose rate decreases to 75 after 2000 hours from the start of measurement. At this time, the rate of decrease in the dose rate is 1.25% (((100-75) / (2000 hours))%). Also, when only a PWM voltage is applied to the comparison UV LED 200, the dose rate decreases to 67.5 after 2000 hours from the start of measurement. At this time, the rate of decrease in the dose rate is 1.63% (((100-67.5) / (2000 hours))%).

[0048] As described above, the degradation suppression method of this embodiment can suppress the decrease in the intensity of the UV LED (dose rate is an example in Figures 5 and 6) due to continued use of the UV LED.

[0049] Next, we will consider the decrease in strength due to the suppression of degradation in this embodiment.

[0050] It is generally known that the degradation of semiconductor devices proceeds through thermal breakdown and electron-hole recombination-enhanced defect reactions (REDRs).

[0051] As in this embodiment, when an overrated voltage is initially applied to the UV LED, the inside of the UV LED (hereinafter referred to as the element as appropriate) is damaged. In other words, by applying an overrated voltage to the UV LED in this way, the composition of the element changes, resulting in improved crystal purity and elimination of lattice strain. As a result, it is presumed that the proliferation of defects due to REDR was suppressed. This is similar to the phenomenon seen in annealing treatment in metal processing. That is, by applying an overrated voltage to the UV LED in the initial stage, an effect similar to annealing (sintering / warming) occurs inside the element, and it is presumed that the proliferation of defects due to REDR was suppressed. Annealing treatment is used in a wide range of materials such as metal processing, resin molded products, and ceramics to improve crystal purity and eliminate internal strain, and is said to lead to improved processing accuracy and strength, thus extending the lifespan of the component.

[0052] In other words, it is presumed that applying an overrated voltage to the UV LED during its initial degradation stage resulted in compositional changes such as improved crystal purity. Furthermore, it is presumed that by stopping the application of this overrated voltage once the degradation of the UV LED had progressed to a certain extent, and continuing to apply a voltage within the UV LED's rated voltage, a state was achieved where further REDR (Reduction in Radiation Recovery) did not progress, thereby suppressing the decrease in intensity. (Second Embodiment) Figure 7 is a second block diagram illustrating the function of the degradation suppression system.

[0053] The degradation suppression system 1 in Figure 7 is the first block diagram in Figure 1 with the addition of a PWM voltage generation unit 121 and a DC voltage generation unit 122. The DC voltage generation unit 122 is a circuit that generates a DC voltage from an AC voltage supplied from a power supply PW2 (a so-called AC-DC conversion circuit). The PWM voltage generation unit 121 generates a PWM voltage from the DC voltage generated by the DC voltage generation unit 122. In this way, the degradation suppression system can be operated whether the power supply voltage is DC or AC. (Examples of UV LED applications) Referring to Figures 8 and 9, an example of an application device (so-called application) of a UV LED in which the degradation suppression process of this embodiment is performed will be described.

[0054] Figure 8 is a schematic cross-sectional view illustrating a first sterilization apparatus having a UV LED on which the degradation suppression process of this embodiment has been performed.

[0055] The sterilization device 3 sterilizes bacteria, viruses, etc., located inside the housing 301, both inside and on the surface of the target object (OBJ). In this specification, "sterilization" also includes inactivating bacteria, viruses, etc.

[0056] The sterilization device 3 comprises a housing 301 and a UV unit 310.

[0057] The UV unit 310 comprises a plurality of UV LEDs 311 on which the degradation suppression process of this embodiment has been performed, and a substrate 312. The substrate 312 is a substrate on which one or more UV LEDs 311 are mounted, and has a cooling function for cooling the UV LEDs 311, a control circuit for the UV LEDs 311, a circuit for supplying power to the UV LEDs 311, etc. The UV unit 310 irradiates the target OBJ inside the housing 301 with ultraviolet light emitted from the UV LEDs 311. This ultraviolet light inactivates bacteria, viruses, etc. inside and on the surface of the target OBJ.

[0058] Figure 9 is a schematic cross-sectional view illustrating a second sterilization apparatus having a UV LED on which the degradation suppression process of this embodiment has been performed.

[0059] The sterilization device 4, for example, sterilizes bacteria, viruses, etc. contained in the water to be treated by irradiating it with ultraviolet light. The water to be treated is water such as tap water or sewage. The water to be treated may be running water or still water.

[0060] The sterilization device 4 comprises a tank 400 and a plurality of UV units 410. The tank 400 comprises side walls 401, a bottom plate 402, a top plate 403, an inlet pipe 404, and an outlet pipe 405. The horizontal cross-sectional shape of the tank 400 can be any shape, such as a rectangle, circle, or ellipse.

[0061] The UV unit 410 comprises a cylinder 411, a UV LED 412 on which the degradation suppression process of this embodiment has been performed, a first substrate 413, and a second substrate 414. The UV unit 410 is detachably fixed to the ceiling plate 403. The cylinder 411 is a cylindrical housing that transmits ultraviolet light emitted from the UV LED 412 to the outside. The first substrate 413 is a long substrate on which a plurality of UV LEDs 412 are mounted and includes a heat sink for cooling the UV LEDs 412. The second substrate 414 has a heat sink that is physically connected to the first substrate 413, as well as a control circuit for the UV LEDs 412 and a circuit that supplies power to the UV LEDs 412.

[0062] The water to be treated flows into the tank 400 from the inlet pipe 404, rises within the tank 400, and flows out of the tank 400 from the outlet pipe 405. The UV unit 410 irradiates the water to be treated in the tank 400 with ultraviolet light emitted from the UV LED 412. This ultraviolet light inactivates bacteria, viruses, etc., in the water to be treated.

[0063] In addition, in Figures 8 and 9, UV LEDs that have not undergone the degradation suppression process may be installed, and the degradation suppression process of this embodiment may be performed during aging of the sterilization device, etc.

[0064] By installing UV LEDs that have undergone the degradation suppression process of this embodiment into various devices such as sterilization equipment, the costs and labor associated with replacing UV LEDs due to degradation can be reduced. [Explanation of symbols]

[0065] 1: Degradation suppression system, 100: Degradation suppression device, 110: Control unit, 120: Voltage application unit, 121: PWM voltage generation unit, 122: DC voltage generation unit, 200: UV LED, PW1: Power supply, PW2: Power supply, 3: Sterilization device, 4: Sterilization device

Claims

1. A method for suppressing the degradation of a semiconductor device that emits electromagnetic waves, A first step of applying a voltage of a first waveform to the semiconductor element, The process includes a second step of applying a voltage with a second waveform, which is different from the first waveform, to the semiconductor element after the first step. The voltage of the first waveform is greater than or equal to the rated voltage of the semiconductor element. A method for suppressing degradation of a semiconductor element, wherein the voltage of the second waveform is less than the rated voltage of the semiconductor element.

2. A method for suppressing the degradation of a semiconductor element that emits electromagnetic waves, A first step of applying a voltage of a first waveform to the semiconductor element, The process includes a second step of applying a voltage with a second waveform, which is different from the first waveform, to the semiconductor element after the first step. The voltage of the first waveform is the voltage of a current greater than or equal to the rated current of the semiconductor element. A method for suppressing degradation of a semiconductor element, wherein the voltage of the second waveform is the voltage of a current less than the rated current of the semiconductor element.

3. A method for suppressing the degradation of a semiconductor device according to claim 1 or claim 2, The electromagnetic wave is ultraviolet light, In the first step, by applying a voltage of the first waveform to the semiconductor element, the intensity of ultraviolet light emitted by the semiconductor element is reduced. A method for suppressing the degradation of a semiconductor element, wherein in the second step, a voltage of the second waveform is applied to the semiconductor element, thereby increasing the intensity of ultraviolet light emitted by the semiconductor element.

4. A method for suppressing the degradation of a semiconductor device according to claim 1 or claim 2, The voltage of the first waveform is a pulse-width modulated voltage, The method for suppressing degradation of the semiconductor element, wherein the voltage of the second waveform is a constant voltage.

5. A method for suppressing the degradation of a semiconductor device according to claim 1 or claim 2, A method for suppressing degradation of a semiconductor element, wherein in at least one of the first and second steps, the power supplied to the semiconductor element is controlled to be constant.

6. A method for suppressing the degradation of a semiconductor device according to claim 3, In the second step, after the increase in intensity, the application of the voltage of the second waveform is continued, thereby reducing the intensity. A method for suppressing the degradation of a semiconductor element, wherein the rate of decrease in strength in the second step is smaller than the rate of decrease in strength in the first step.

Images