Test equipment

Abstract

The present invention provides a test apparatus capable of controlling a transistor independently of the voltage supplied to the voltage supply terminal. [Solution] The test apparatus comprises a voltage supply terminal to which a voltage is supplied, a first reference potential terminal and a second reference potential terminal to which a reference potential is supplied, a first terminal to which the first end of the element under test is electrically connected, a second terminal to which the second end of the element under test is electrically connected and to which the first reference potential terminal is electrically connected, a source electrically connected to the voltage supply terminal, a drain electrically connected to the first terminal, and a gate, a clamping element electrically connected between the voltage supply terminal and the gate, which clamps the voltage difference between the voltage supply terminal and the gate to a predetermined value when current flows between the voltage supply terminal and the gate, a first switch that connects or disconnects the gate and the second reference potential terminal, and a control circuit that switches the first switch from the disconnected state to the connected state when the voltage is supplied to the voltage supply terminal.

Description

Technical Field

[0001] The present disclosure relates to a test apparatus.

Background Art

[0002] There is known a test apparatus that applies a desired voltage to a test element (for example, Patent Document 1).

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] When a test apparatus applies a voltage to a test element, there is a method in which after electrically connecting a voltage source to the test element, the voltage source applies a voltage to the test element. In this method, the time dependence of the voltage applied to the test element is large. Therefore, a transistor is connected as a switch between the voltage supply terminal to which the voltage is supplied and the test element, and the transistor is switched from the off state to the on state while the voltage is supplied to the voltage supply terminal. Thereby, the time dependence of the voltage applied to the test element can be reduced. However, if the voltage applied to the gate of the transistor is not controlled according to the voltage supplied to the voltage supply terminal, an overvoltage may be applied to the transistor.

[0005] An object of the present disclosure is to provide a test apparatus capable of controlling a transistor without depending on the voltage supplied to the voltage supply terminal.

Means for Solving the Problems

[0006] Embodiments of the present disclosure are test apparatus comprising: a voltage supply terminal to which a voltage is supplied; a first reference potential terminal and a second reference potential terminal to which a reference potential is supplied; a first terminal to which the first end of the element under test is electrically connected; a second terminal to which the second end of the element under test is electrically connected and to which the first reference potential terminal is electrically connected; a source electrically connected to the voltage supply terminal; a drain electrically connected to the first terminal; and a gate; a clamping element electrically connected between the voltage supply terminal and the gate, which clamps the voltage difference between the voltage supply terminal and the gate to a predetermined value when current flows between the voltage supply terminal and the gate; a first switch for connecting or disconnecting the gate and the second reference potential terminal; and a control circuit for switching the first switch from a disconnected state to a connected state when the voltage is supplied to the voltage supply terminal. [Effects of the Invention]

[0007] According to this disclosure, the transistor can be controlled independently of the voltage supplied to the voltage supply terminal. [Brief explanation of the drawing]

[0008] [Figure 1] This is a circuit diagram of the test apparatus according to the first embodiment. [Figure 2] This is a timing chart showing the operation of the test apparatus in the first embodiment. [Figure 3] This is a circuit diagram of the test apparatus for the comparative configuration. [Figure 4] This is a block diagram of the test apparatus according to the second embodiment. [Figure 5] This is a timing chart showing the operation of the test apparatus in the second embodiment. [Figure 6] This is a cross-sectional view of a light-emitting element, which is an example of a device under test. [Figure 7] This is a circuit diagram of the test apparatus according to the third embodiment. [Modes for carrying out the invention]

[0009] The embodiments for implementing this disclosure will be described in detail below with reference to the drawings. The embodiments described below are examples for embodying the technical concept of the invention and do not limit this disclosure to the configurations and numerical values ​​described. In each drawing, the same reference numerals are used for the same components, and redundant explanations may be omitted as appropriate. The size, positional relationships, etc., of each component shown in each drawing may be exaggerated to facilitate understanding of the invention.

[0010] (First Embodiment) Figure 1 is a circuit diagram of the test apparatus according to the first embodiment. The test apparatus 100 includes a voltage supply terminal TV, a first reference potential terminal TG1, a second reference potential terminal TG2, a first terminal T1, a second terminal T2, a transistor Q1, a second switch SW2, a drive circuit 10, and a control circuit 12.

[0011] The voltage supply terminal TV is supplied with the voltage VH to be applied to the element under test 20. The first reference potential terminal TG1 and the second reference potential terminal TG2 are supplied with a reference potential such as ground potential. The first reference potential terminal TG1 and the second reference potential terminal TG2 may be electrically connected in common to the reference potential terminal or reference potential layer to which the reference potential is supplied. The first terminal T1 is electrically connected to the first end TA of the element under test 20. The second terminal T2 is electrically connected to the second end TB of the element under test 20. The first terminal T1 and the first end TA are detachable, and the second terminal T2 and the second end TB are detachable. By replacing the element under test 20, it is possible to test different elements under test 20. The voltage applied between the first end TA and the second end TB of the element under test 20 is VD.

[0012] Transistor Q1 has a source S electrically connected to the voltage supply terminal TV, a drain D electrically connected to the first terminal T1, and a gate G. Transistor Q1 is a p-channel transistor, for example, a p-channel MOSFET (Metal Oxide Semiconductor Field Effect Transistor). Transistor Q1 functions as a high-side switch.

[0013] The second switch SW2 is, for example, a transistor Q2, which is electrically connected between the second terminal T2 and the first reference potential terminal TG1. Transistor Q2 has a source S electrically connected to the first reference potential terminal TG1, a drain D electrically connected to the second terminal T2, and a gate G. Transistor Q2 is an n-channel transistor, for example, an n-channel MOSFET. Transistor Q2 functions as a low-side switch. The drive circuit 10 drives transistor Q1 by applying a gate voltage VG to the gate G of transistor Q1. The control circuit 12 controls transistors Q1 and Q2.

[0014] The drive circuit 10 includes a clamp element 14, a first switch SW1, and a first resistor R1, a second resistor R2, and a resistor R3. The clamp element 14 is electrically connected between nodes N1 and N2. Node N1 is a node electrically connected to the voltage supply terminal TV. Node N2 is a node electrically connected to the gate G of transistor Q1 via the resistor R3. Diodes D1 to D3 are forward in the direction from node N1 to N2. The first switch SW1 is transistor Q3, which is connected in series with the first resistor R1 between node N2 and the second reference potential terminal TG2. Transistor Q3 has a source S electrically connected to the second reference potential terminal TG2, a drain D electrically connected to node N2 via the first resistor R1, and a gate G. Transistor Q3 is an n-channel transistor, for example, an n-channel MOSFET. The second resistor R2 is connected in parallel with the clamp element 14 between nodes N1 and N2. The control circuit 12 controls the gate voltages of transistors Q2 and Q3 to control transistors Q1 to Q3 to either an connected or disconnected state.

[0015] Figure 2 is a timing chart showing the operation of the test apparatus in the first embodiment. Figure 2 shows, with respect to time, the connection state and disconnection state of the first switch SW1, the gate voltage VG of the transistor Q1, the connection state and disconnection state of the transistor Q1, the connection state and disconnection state of the second switch SW2, and the voltage VD applied to the device under test 20.

[0016] As shown in Figure 2, between times t0 and t2, the control circuit 12 applies a reference potential (e.g., 0V) to the gate of the transistor Q3. Thereby, the first switch SW1 is in the disconnected state. The node N2 is disconnected from the second reference potential terminal TG2. Thus, the voltage VH of the voltage supply terminal TV is applied to the gate G of the transistor Q1 via the second resistance element R2 and the resistance element R3. The resistance values of the second resistance element R2 and the resistance element R3 are set sufficiently lower than the gate impedance of the transistor Q1. Thereby, the gate voltage VG of the transistor Q1 becomes substantially the voltage VH. Thus, the transistor Q1 is in the disconnected state.

[0017] Between times t0 and t2, the control circuit 12 applies a reference potential (e.g., 0V) to the gate of the transistor Q2. Thereby, the second switch SW2 is in the disconnected state. Since the transistor Q1 and the second switch SW2 are in the disconnected state, no voltage is applied to the device under test 20 and it becomes floating F.

[0018] At time t2, the control circuit 12 applies, for example, a predetermined positive voltage with respect to the reference potential as the voltage for making the transistor Q3 conductive to the gate of the transistor Q3. As a result, the first switch SW1 changes from the off state to the on state. The voltage at the node N2 tends to be the voltage obtained by resistively dividing the voltage VH by the first resistor element R1 and the second resistor element R2. When a current flows between the nodes N1 and N2, the clamping element 14 clamps the voltage difference between the nodes N1 and N2 to a positive predetermined value ΔV. The clamping element 14 is, for example, diodes D1 to D3 with the direction from the node N1 to N2 being the forward direction. In this case, the predetermined value ΔV is the forward voltage drop of the diodes D1 to D3. The predetermined value ΔV can be appropriately set according to the number etc. of the diodes D1 to D3. As described above, the gate voltage VG becomes VH - ΔV, and the transistor Q1 becomes conductive.

[0019] At time t2, the control circuit 12 applies, for example, a predetermined positive voltage with respect to the reference potential as the voltage for making the transistor Q2 conductive to the gate of the transistor Q2. As a result, the second switch SW2 changes from the off state to the on state. At time t2, since the transistor Q1 and the second switch SW2 become conductive almost simultaneously, a voltage VH is applied as the voltage VD between the first terminal TA and the second terminal TB of the DUT 20.

[0020] Between time t2 and t3, the control circuit 12 maintains the transistors Q2 and Q3 in the conductive state. As a result, the transistor Q1 is maintained in the conductive state, and the voltage VD is maintained at the voltage VH.

[0021] At time t3, the control circuit 12 applies the reference potential to the gate of the transistor Q3. The first switch SW1 changes from the on state to the off state. The gate voltage VG becomes VH, and the transistor Q1 becomes non - conductive. The control circuit 12 applies the reference potential to the gate of the transistor Q2. As a result, the second switch SW2 changes from the on state to the off state. The voltage VD of the DUT 20 becomes floating.

[0022] (Comparative form) Figure 3 is a path diagram of the test apparatus for the comparative configuration. In the test apparatus 110 for the comparative configuration, there is no drive device, and the control circuit 12 applies the gate voltage VG to the gate G of transistor Q1.

[0023] As in the comparative configuration, the reason for placing a high-side switch between the first terminal TA of the element under test 20 and the voltage supply terminal TV, and a low-side switch between the element under test 20 and the first reference potential terminal TG1 is as follows: When applying a voltage VD to the element under test 20, the first terminal TA of the element under test 20 is connected to the voltage supply terminal TV, and the second terminal TB is connected to the first reference potential terminal TG1. The voltage source supplying voltage to the voltage supply terminal TV applies the desired voltage VD0, thereby applying the desired voltage VD0 to the element under test 20. However, with this method, when the voltage source applies the voltage VD0, the voltage VD applied to the element under test 20 becomes time-dependent depending on the impedance conditions of the test equipment including the voltage source. For example, the voltage VD gradually decreases from 0V to VD0. Or, the voltage VD overshoots beyond VD0 before becoming VD0. If such a voltage VD is time-dependent, for example, when measuring the time it takes for the element under test 20 to be destroyed by applying a constant voltage to it, it becomes impossible to measure the time accurately.

[0024] In the comparative test apparatus 110, when voltage VH is supplied to the voltage supply terminal TV and a reference potential is supplied to the first reference potential terminal TG1, transistors Q1 and Q2 are switched from the disconnected state to the connected state. This reduces the time dependence of the voltage applied to the element under test 20. Therefore, for example, when measuring the time until the element under test 20 is destroyed by applying a constant voltage to it, accurate time measurement is possible.

[0025] A p-channel transistor is in a closed state when the same voltage is applied to the gate G relative to the source S, and in a connected state when a negative voltage (for example, between -10V and -5V) is applied to the gate G relative to the source S. Therefore, the control circuit 12 generates voltage VH and voltage VH-ΔV as the gate voltage VG and supplies them to the gate G of transistor Q1. However, if the voltage value of voltage VH is changed to a different voltage value, the voltage values ​​of voltage VH and voltage TH-ΔV applied to the gate G must also be changed. Transistor Q1 will be damaged if the voltage difference between the gate G and the source S becomes too large. Therefore, the value of ΔV must be kept within a certain range. Under these conditions, the control circuit 12 generates voltage VH and voltage VH-ΔV as the gate voltage VG, but the circuit for generating such voltage values ​​becomes complex.

[0026] (Description of the first embodiment) According to the first embodiment, the clamp element 14 is electrically connected between the voltage supply terminal TV and the gate G of transistor Q1. When current flows between the voltage supply terminal TV and the gate G of transistor Q1, the clamp element 14 clamps the voltage difference between the voltage supply terminal TV and the gate G of transistor Q1 to a predetermined value ΔV. As a result, the control circuit 12 can control transistor Q1 using a simple drive circuit 10 by controlling the first switch SW1, which connects or disconnects the gate G of transistor Q1 and the second reference potential terminal TG2, using normal low and high levels. Therefore, transistor Q1 can be controlled without using a complex drive circuit and without depending on the voltage VH supplied to the voltage supply terminal TV.

[0027] Without using the second switch SW2, the second terminal T2 may be electrically connected to the first reference potential terminal TG1 and electrically short-circuited. In this case as well, the gate voltage VG of transistor Q1 will generate voltages VH and VH-ΔV, and the drive circuit 10 can be used.

[0028] The second switch SW2 connects or disconnects the second terminal T2 and the first reference potential terminal TG1. When the control circuit 12 switches the first switch SW1 from the disconnected state to the connected state, it also switches the second switch SW2 from the disconnected state to the connected state. As a result, when a voltage VH is applied to the first terminal TA of the element under test 20, a reference potential is applied to the second terminal TB.

[0029] If the first switch SW1 and the second switch SW2 are n-channel transistors, then the first switch SW1 and the second switch SW2 are controlled by the same high and low levels. For example, the low level is the reference potential, and the high level is a voltage that is a predetermined voltage higher than the reference potential. As a result, the control circuit 12 only needs to generate the high and low levels, which simplifies the circuit configuration of the control circuit 12.

[0030] As shown at time t2 in Figure 2, the control circuit 12 simultaneously switches the first switch SW1 and the second switch SW2 from the disconnected state to the connected state. As a result, potential is supplied to the first terminal TA and the second terminal TB simultaneously, which reduces the time dependence of the voltage VD when the voltage VH is applied to the element under test 20. Simultaneous switching of the first switch SW1 and the second switch SW2 means that the difference in the switching times of the first switch SW1 and the second switch SW2 is, for example, within a range of 1 microsecond or less.

[0031] In the drive circuit 10, there may be a delay between switching the first switch SW1 from the disconnected state to the connected state and the transistor Q1 switching from the disconnected state to the connected state. In this case, the control circuit 12 may switch the second switch SW2 from the disconnected state to the connected state after switching the first switch SW1 from the disconnected state to the connected state, so that transistor Q1 and the second switch SW2 switch from the disconnected state to the connected state simultaneously.

[0032] At time t3, the control circuit 12 simultaneously switches the first switch SW1 and the second switch SW2 from the connected state to the disconnected state. As a result, the voltage is simultaneously cut off at the first terminal TA and the second terminal TB, which reduces the time dependence of the voltage VD.

[0033] The first resistor R1 is electrically connected in series with the first switch SW1 between the gate G of transistor Q1 and the second reference potential terminal TG2. This prevents node N2 from becoming the reference potential when the first switch SW1 is connected.

[0034] The second resistor R2 is electrically connected in parallel with the clamp element 14 between the voltage supply terminal TV and the gate G of transistor Q1. As a result, if the resistance value of the second resistor R2 is sufficiently lower than the resistance value of the clamp element 14 at a constant voltage, the gate voltage VG can be made approximately VH when the first switch SW1 is closed. The resistance value of the second resistor R2 is, for example, 10% or less, and 1% or less, of the resistance value of the clamp element 14 at a constant voltage.

[0035] When voltage VH is higher than the reference potential, transistor Q1 is a p-channel transistor. This means that transistor Q1 can be connected by setting the gate voltage VG to a voltage lower than voltage VH. For example, if transistor Q1 were an n-channel transistor, a voltage higher than VH would need to be applied to the gate voltage VG to connect it, resulting in a more complex drive circuit.

[0036] The clamp element 14 consists of diodes D1 to D3, where the direction of the gate G of transistor Q1 is forward from the voltage supply terminal TV. This allows a predetermined value ΔV to be set by the forward voltage drop across the diodes.

[0037] (Second Embodiment) The second embodiment is an example of measuring the characteristics of the element under test 20 when no voltage VH is applied to the element under test 20. Figure 4 is a block diagram of the test apparatus 102 according to the second embodiment. As shown in Figure 4, the test apparatus 102 of the second embodiment includes switches SW3 and SW4, a control device 15, a measuring unit 16, an ammeter 17, and a voltage source 18, in addition to the test apparatus 100 of the first embodiment.

[0038] The voltage source 18 supplies voltage TH to the voltage supply terminal TV. The ammeter 17 measures the current flowing through the element under test 20. Switch SW3 is electrically connected between the measurement unit 16 and the first terminal T1. Switch SW4 is electrically connected between the measurement unit 16 and the second terminal T2. The measurement unit 16 measures the electrical characteristics of the element under test 20. The control device 15 is, for example, a computer, which controls the control circuit 12 and the measurement unit 16. Switches SW3 and SW4 are connected or disconnected based on the control signals C1 and C2 of the control device 15.

[0039] Figure 5 is a timing chart showing the operation of the test apparatus in the second embodiment. Figure 5 shows the voltage at the voltage supply terminal TV, the connected and disconnected states of transistor Q1, the connected and disconnected states of the second switch SW2, the connected and disconnected states of switches SW3 and SW4, and the operation of the measurement unit 16 and the control device 15 over time.

[0040] As shown in Figure 5, at time t0, the control device 15 instructs the voltage source 18 to supply 0V to the voltage supply terminal TV. The control device 15 instructs the control circuit 12 to turn off transistor Q1, the second switch SW2, and switches SW3 and SW4. At time t2, the control device 15 instructs the voltage source 18 to output voltage VH to the voltage supply terminal TV. At time t2, the control device 15 instructs the control circuit 12 to switch transistor Q1 and the second switch SW2 from the turned-off state to the connected state. At time t3, after a set period has elapsed from time t2, the control device 15 instructs the control circuit 12 to switch transistor Q1 and the second switch SW2 from the connected state to the turned-off state. As a result, voltage VH is applied to the element under test 20 during the period from time t2 to t3.

[0041] During the period from time t2 to t3, if the current value measured by the ammeter 17 is abnormal, the control device 15 may switch the transistor Q1 and the second switch SW2 from the connected state to the disconnected state. For example, if the current value measured by the ammeter 17 becomes approximately 0, it is possible that the element under test 20 has been destroyed and opened. Also, if the current value measured by the ammeter 17 becomes much larger than a predetermined value, it is possible that the element under test 20 has been destroyed and short-circuited. In such cases, the control device 15 may switch the transistor Q1 and the second switch SW2 to the disconnected state without waiting for the set period to elapse, causing the voltage source 18 to output 0V to the voltage supply terminal TV.

[0042] At time t4, the control device 15 causes the voltage source 18 to output 0V to the voltage supply terminal TV. At time t5, the control device 15 switches switches SW3 and SW4 from the disconnected state to the connected state. As a result, the measurement unit 16 is electrically connected to the element under test 20. During the period from time t6 to t7, the control device 15 causes the measurement unit 16 to measure the electrical characteristics of the element under test 20. At time t8, the control device 15 switches switches SW3 and SW4 from the connected state to the disconnected state. As a result, the measurement unit 16 is electrically disconnected from the element under test 20.

[0043] Subsequently, the control device 15 acquires the results measured by the measurement unit 16 and determines the electrical characteristics of the element under test 20. For example, the control device 15 determines whether the electrical characteristics of the element under test 20 change within a predetermined range before and after the application of voltage VH. The control device 15 determines that the change in the electrical characteristics of the element under test 20 is normal if it is within the predetermined range, and that it is abnormal if it has changed beyond the predetermined range. After replacing the element under test 20, the control device 15 performs the operation again from time t0.

[0044] (Example of the element under test 20) As an example of the element under test 20, a diode element will be described. Examples of diode elements include LEDs (Light Emitting Diodes), LDs (Laser Diodes), and diodes used in electronic circuits.

[0045] Figure 6 is a cross-sectional view of a light-emitting element as an example of a device under test. As shown in Figure 6, the light-emitting element 30 comprises a substrate 31, an n-side semiconductor layer 32, an active layer 33, a p-side semiconductor layer 34, an n-side electrode 35, a p-side electrode 36, and a protective film 37. The substrate 31 is a conductive substrate. The n-side semiconductor layer 32, the active layer 33, and the p-side semiconductor layer 34 are arranged on the substrate 31 in this order. The n-side semiconductor layer 32 and the p-side semiconductor layer 34 include a cladding layer. The active layer 33 has, for example, an MQW (Multi Quantum Wall) structure and emits light. The n-side electrode 35 is electrically connected to the substrate 31. The p-side electrode 36 is electrically connected to the p-side semiconductor layer 34. The protective film 37 is an insulating film that covers the n-side semiconductor layer 32, the active layer 33, and the p-side semiconductor layer 34. The substrate 31, the n-side semiconductor layer 32, the active layer 33, and the p-side semiconductor layer 34 are, for example, nitride semiconductor layers. Nitride semiconductor layers are, for example, x Al y Ga 1-x-y This is a layer of N (0≦x≦1, 0≦y≦1, x+y≦1).

[0046] Applying a forward or reverse voltage exceeding the rated voltage to a diode element will destroy the diode element. Therefore, the voltage at which the diode element is destroyed and the destruction mechanism are evaluated by applying a voltage exceeding the rated voltage to the diode element. The test apparatus 102 of the second embodiment is used for this evaluation. By using the test apparatus 102, when voltage VH is supplied to the voltage supply terminal TV, the transistor Q1 and the second switch SW2 are switched to the connected state. This reduces the time dependence of the voltage VD applied to the element under test 20. Thus, the voltage at which the diode element is destroyed and the destruction mechanism can be evaluated with high accuracy.

[0047] For example, let's consider measuring the voltage at which diode elements from the same manufacturing lot are destroyed. Using the method in Figure 5, a voltage VD1 is applied to one diode element from a group of diode elements from the same manufacturing lot to determine whether or not the diode element is destroyed. If it is not destroyed, a voltage VD2, higher than VD1, is applied to another diode element from the same manufacturing lot using the method in Figure 5 to determine whether or not the diode element is destroyed. In this way, different voltages are applied to diode elements from the same manufacturing lot to evaluate the voltage at which the diode element is destroyed. The electrical characteristic used to determine whether or not a diode element is destroyed is, for example, the forward voltage when a predetermined forward current is passed through the diode element.

[0048] The failure mode can also be estimated based on the time elapsed from the application of a voltage VD to the diode element until the diode element is destroyed. For example, the destruction of the pn junction of a diode element occurs in a short time. The melting of the bonding wires that electrically connect the diode elements occurs over a long time because it is caused by Joule heating. Therefore, the control device 15 can also estimate the failure mode of the diode element based on the time elapsed from time t2 in Figure 5 until the current value of the ammeter 17 becomes abnormal. In the test apparatus 102 of the second embodiment, the time dependence of the voltage VD applied to the diode element is small, so the time until the diode element is destroyed can be measured with high accuracy. Thus, the accuracy of estimating the failure mode in the diode element can be improved.

[0049] Alternatively, using multiple diode elements from the same manufacturing lot, the voltage at which a diode element is destroyed can be evaluated. Then, a voltage near the voltage at which the diode element is destroyed can be applied to the diode element, and the time until the diode element is destroyed can be measured to estimate the failure mode.

[0050] Although a diode element was used as an example for the element under test 20, the element under test 20 may also be a semiconductor element such as a transistor, or any other electronic element.

[0051] As described above, according to the second embodiment, the measuring unit 16 is electrically connected to the first terminal T1 and the second terminal T2 when the first switch SW1 and the second switch SW2 are in the off state, and measures the characteristics of the element under test 20. This makes it possible to measure the electrical characteristics of the element under test 20 before or after a voltage VH is applied to the element under test 20.

[0052] The ammeter 17 measures the current flowing through the element under test 20 when the first switch SW1 is connected. This allows us to determine whether or not the diode element was destroyed between times t2 and t3 in Figure 5, when the voltage VH is applied to the element under test 20.

[0053] The voltage source 18 can change the voltage value supplied to the voltage supply terminal TV. This allows different voltages to be applied to the element under test 20. The drive circuit 10 can control transistor Q1 with a simple circuit configuration even when different voltages are applied to the element under test 20.

[0054] (Third embodiment) Figure 7 is a circuit diagram of the test apparatus according to the third embodiment. As shown in Figure 7, the test apparatus 104 of the third embodiment is equipped with transistors Q1A, Q2A, and Q3A instead of transistors Q1, Q2, and Q3. The clamp element 14 is equipped with diodes D1A to D3A instead of diodes D1 to D3. A negative voltage VL relative to the reference potential is supplied to the voltage supply terminal TV. The other configurations are the same as in Figure 1 of the first embodiment and will not be described further.

[0055] As in the third embodiment, when the voltage VL supplied to the voltage supply terminal TV is lower than the reference potential, transistor Q1A is made an n-channel transistor. Transistors Q2A and Q3A are made p-channel transistors. The clamp element 14 is made of diodes D1A to D3A, whose direction of gate G of transistor Q1A is reversed from the voltage supply terminal TV. This allows the device to operate in the same way as the test devices 100 and 102 of the first and second embodiments.

[0056] Although preferred embodiments have been described in detail above, the invention is not limited to the embodiments described above, and various modifications and substitutions can be made to the embodiments described above without departing from the scope of the claims.

[0057] The light-emitting element according to the embodiments of this disclosure includes, for example, the following embodiments. (Section 1) Voltage supply terminals to which voltage is supplied, A first reference potential terminal and a second reference potential terminal to which a reference potential is supplied, The first terminal to which the first end of the element under test is electrically connected, The second terminal of the element under test is electrically connected to the second terminal to which the first reference potential terminal is electrically connected, A transistor having a source electrically connected to the voltage supply terminal, a drain electrically connected to the first terminal, and a gate, A clamping element is electrically connected between the voltage supply terminal and the gate, and clamps the voltage difference between the voltage supply terminal and the gate to a predetermined value when current flows between the voltage supply terminal and the gate. A first switch that connects or disconnects the gate and the second reference potential terminal, A control circuit that switches the first switch from an off state to an on state when the voltage is supplied to the voltage supply terminal, A test apparatus equipped with the following features. (Section 2) The device includes a second switch that connects or disconnects the second terminal and the first reference potential terminal, The test apparatus according to item 1, wherein the control circuit switches the second switch from the disconnected state to the connected state when the first switch is switched from the disconnected state to the connected state. (Section 3) The test apparatus according to item 2, wherein the control circuit switches the first switch and the second switch simultaneously from an disconnected state to an connected state. (Section 4) The test apparatus according to item 2 or 3, comprising a measuring unit that is electrically connected to the first terminal and the second terminal and measures the characteristics of the element under test when the first switch and the second switch are in the off state. (Section 5) The test apparatus according to any one of claims 1 to 3, comprising a first resistive element electrically connected in series with the first switch between the gate and the second reference potential terminal. (Section 6) The test apparatus according to item 5, further comprising a second resistive element electrically connected in parallel with the clamping element between the voltage supply terminal and the gate. (Section 7) The test apparatus according to any one of items 1 to 6, wherein the voltage is higher than the reference potential and the transistor is a p-channel transistor. (Section 8) The test apparatus according to item 7, wherein the clamping element is a diode whose gate is forward from the voltage supply terminal. (Section 9) The test apparatus according to any one of claims 1 to 6, wherein the voltage is lower than the reference potential and the transistor is an n-channel transistor. (Section 10) The test apparatus according to item 9, wherein the clamping element is a diode whose gate direction is reversed from the voltage supply terminal. (Section 11) The test apparatus according to any one of claims 1 to 10, further comprising an ammeter for measuring the current flowing through the element under test when the first switch is connected. (Section 12) The voltage supply terminal is provided with a voltage source that supplies the voltage, The test apparatus according to any one of claims 1 to 11, wherein the voltage value of the aforementioned voltage is changeable. (Section 13) The test apparatus according to any one of claims 1 to 12, wherein the element under test is a diode. [Explanation of Symbols]

[0058] 10 Drive circuit 12 Control circuits 14 Clamping elements 15 Control device 16 Measuring part 17 Ammeter 18 Voltage source 20 Elements under test 30 light-emitting elements

Claims

1. Voltage supply terminals to which voltage is supplied, A first reference potential terminal and a second reference potential terminal to which a reference potential is supplied, The first terminal to which the first end of the element under test is electrically connected, The second terminal of the element under test is electrically connected to the second terminal to which the first reference potential terminal is electrically connected, A transistor having a source electrically connected to the voltage supply terminal, a drain electrically connected to the first terminal, and a gate, A clamping element is electrically connected between the voltage supply terminal and the gate, and clamps the voltage difference between the voltage supply terminal and the gate to a predetermined value when current flows between the voltage supply terminal and the gate. A first switch that connects or disconnects the gate and the second reference potential terminal, A control circuit that switches the first switch from an off state to an on state when the voltage is supplied to the voltage supply terminal, A test apparatus equipped with the following features.

2. The system includes a second switch that connects or disconnects the second terminal and the first reference potential terminal. The test apparatus according to claim 1, wherein the control circuit switches the second switch from the disconnected state to the connected state when the first switch is switched from the disconnected state to the connected state.

3. The test apparatus according to claim 2, wherein the control circuit switches the first switch and the second switch simultaneously from an off state to an on state.

4. The test apparatus according to claim 2 or 3, further comprising a measuring unit that is electrically connected to the first terminal and the second terminal and measures the characteristics of the element under test when the first switch and the second switch are in the off state.

5. The test apparatus according to any one of claims 1 to 3, further comprising a first resistive element electrically connected in series with the first switch between the gate and the second reference potential terminal.

6. The test apparatus according to claim 5, further comprising a second resistive element electrically connected in parallel with the clamping element between the voltage supply terminal and the gate.

7. The test apparatus according to any one of claims 1 to 3, wherein the voltage is higher than the reference potential and the transistor is a p-channel transistor.

8. The test apparatus according to claim 7, wherein the clamping element is a diode whose gate is forward from the voltage supply terminal.

9. The test apparatus according to any one of claims 1 to 3, wherein the voltage is lower than the reference potential and the transistor is an n-channel transistor.

10. The test apparatus according to claim 9, wherein the clamping element is a diode whose gate direction is reversed from the voltage supply terminal.

11. The test apparatus according to any one of claims 1 to 3, further comprising an ammeter for measuring the current flowing through the element under test when the first switch is connected.

12. The voltage supply terminal is provided with a voltage source that supplies the voltage, The test apparatus according to any one of claims 1 to 3, wherein the voltage value of the aforementioned voltage is changeable.

13. The test apparatus according to any one of claims 1 to 3, wherein the element under test is a diode.

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