Photorelay

Abstract

The embodiment provides a photorelay with low transmission loss of high-frequency signals. The photorelay of the embodiment comprises: a polyimide substrate having a first surface and a second surface opposite to the first surface, with a thickness of 10 μm or more and 120 μm or less; an input terminal on the second surface; an output terminal on the second surface; a light receiving element on the first surface; a light emitting element on the light receiving element; and a MOSFET on the first surface.

Description

[0001] Related applications

[0002] This application enjoys priority based on Japanese Patent Application No. 2019-219567 (filed on December 4, 2019). This application incorporates the entire contents of the basic application by reference to that basic application. Technical Field

[0003] The embodiments of the present invention relate to optical relays. Background Technology

[0004] An opto-relay containing an optically coupled insulating circuit can convert an input electrical signal into a light signal using a light-emitting element, and then output an electrical signal after being received by a light-receiving element. Therefore, an opto-relay can transmit electrical signals while maintaining isolation between the input and output.

[0005] Optical relays for AC loads are mostly used in semiconductor testers used to inspect semiconductor integrated circuits, etc. With the increasing demand for broadband DRAM (Dynamic Random Access Memory) and the like, there is a need for optical relays that can pass high-frequency signals with frequencies higher than a few GHz with low loss.

[0006] Optical relays have an output circuit that uses a MOSFET (Metal-Oxide-Semiconductor Field-Effect Transistor) to switch signals in response to the on / off state of an input electrical signal. Therefore, optical relays that exhibit high high-frequency characteristics are required when the light-emitting element, light-receiving element, or MOSFET is mounted on the mounting substrate of a semiconductor tester. Summary of the Invention

[0007] The implementation provides an optical relay with low transmission loss for high-frequency signals.

[0008] The photorelay of the embodiment includes: a polyimide substrate having a first side and a second side opposite to the first side, with a thickness of 10 μm or more and 120 μm or less; an input terminal on the second side; an output terminal on the second side; a light-receiving element on the first side; a light-emitting element on the light-receiving element; and a MOSFET on the first side. Attached Figure Description

[0009] Figure 1 This is a schematic perspective view of the optical relay in the embodiment.

[0010] Figure 2 This is a schematic cross-sectional view of the optical relay in the embodiment.

[0011] Figure 3 This is a schematic diagram of the optical relay in the implementation method.

[0012] Figure 4 This is an example of a circuit diagram for measuring transmission loss.

[0013] Figure 5 It is a graph that shows the high-frequency transmission characteristics relative to the frequency. Detailed Implementation

[0014] Hereinafter, embodiments of the present invention will be described with reference to the accompanying drawings.

[0015] Figure 1 This is a schematic perspective view of the optical relay in the embodiment. Figure 2 This is a schematic cross-sectional view of the optical relay in the embodiment.

[0016] The photorelay 100 includes: a mounting component 5; a MOSFET 70 (71) bonded to the output terminals 31 and 32 of the mounting component 5; a light-receiving element 50 bonded to a die pad 41 and having a light-receiving surface on its upper surface; a light-emitting element 60 that illuminates the light-receiving surface; an adhesive layer 52 that is both transparent and insulating, and bonds the light-emitting element 60 to the upper surface of the light-receiving element 50; and a sealing resin layer 90. For example, an LED (Light Emitting Diode) can be used in the light-emitting element 60. Furthermore, a photodiode, phototransistor, or light-receiving IC can be used in the light-receiving element 50.

[0017] In this figure, MOSFET70(71) is shown as two elements with a common source connection. However, the invention is not limited to this and can also be a single MOSFET. If the back side of each MOSFET70 chip is set as the drain, then the output terminals 31 and 32 are connected to the drain of each MOSFET.

[0018] The first sealing resin layer 90 covers the light-receiving element 50, the light-emitting element 60, the MOSFET 70 (71), and the first surface 10a of the polyimide substrate 10, and protects the interior. The light-emitting element 60 may also be sealed by a second sealing resin 91.

[0019] The polyimide substrate 10 has a rectangular first surface 10a and a second surface 10b opposite to the first surface 10a. In addition, through holes 11 (11a, 11b, 11c, 11d) can be provided from the first surface 10a to the second surface 10b.

[0020] The polyimide substrate 10 is preferably set to a thickness of 10 μm or more and 120 μm or less. This allows for improved throughput characteristics in the 15 GHz to 30 GHz high-frequency band by using an extremely thin polyimide substrate 10. From the viewpoint of improving throughput characteristics in the high-frequency band, the thickness of the polyimide substrate 10 is preferably 10 μm or more and 100 μm or less. From the viewpoint of improving throughput characteristics in higher-frequency bands above 20 GHz, the thickness of the polyimide substrate 10 is preferably 10 μm or more and 60 μm or less, more preferably 10 μm or more and 30 μm or less. It is preferable to further improve the throughput characteristics in higher-frequency bands by reducing the thickness of the polyimide substrate 10, for example, to 60 μm or less. Because the polyimide substrate 10 is thin, the plating formed on the polyimide substrate 10 easily fills the through-holes 11, and in addition to the substrate itself, the high-frequency throughput characteristics can be improved through the wiring characteristics.

[0021] The input terminal section 20, for example, has two input terminal sections 21 and 22. Each input terminal section 21 and 22 connects a first conductive region 21a and 22a provided on the first surface 10a to an input terminal 21c and 22c provided on the second surface 10b via through-hole wiring 21b and 21b provided in through holes 11a and 11b, respectively. The first conductive regions 21a and 22a are so-called pads.

[0022] The output terminal section, for example, has two output terminal sections 31 and 32. Each output terminal section 31 and 32 connects a second conductive region 31a and 32a provided on the first surface 10a to an output terminal 31c and 32c provided on the second surface 10b via through-hole wiring 31a and 31b provided in through holes 11c and 11d. The second conductive regions 31a and 32a are so-called pads. If the thickness of the second conductive regions 31a and 32a (pads) is too thick, the high-frequency transmission characteristics are reduced.

[0023] The input terminals 21 and 22, the output terminals 31 and 32, and the chip pads 41 can be constructed from a Cu foil disposed on the surface of the polyimide substrate 10, and plating layers such as Ni and Au stacked thereon. Furthermore, when viewed from above, the input terminals 21 and 22, the output terminals 31 and 32, and the chip pads 41 are separated from each other on the polyimide substrate 10 and are insulated from each other.

[0024] The through-holes 11c and 11d (through-hole wiring 31b and 32b) on the MOSFEET 70 and 71 sides are preferably multiple. By having multiple through-holes 11c and 11d, the high-frequency throughput characteristics can be improved.

[0025] The diameters of the via wirings 31b and 32b in the through holes 11c and 11d on the MOSFEET 70 and 71 sides are preferably 20 μm or more and 40 μm or less. If the diameters of the through holes 11c and 11d are too large, plating will be difficult, and the via wirings 31b and 32b will not completely fill the through holes 11c and 11d, which is therefore not preferred. From the same point of view, the diameters of the via wirings 31b and 32b are more preferably 25 μm or more and 35 μm or less.

[0026] The input terminal 21 is electrically connected to the cathode pad 81f of the light-emitting element 60 via the bonding wire BW1.

[0027] The input terminal 22 is electrically connected to the pad 81e of the anode of the light-emitting element 60 via the bonding wire BW2.

[0028] The light-receiving element 50 is electrically connected to the gate and source of MOSFETs 70 and 71 via bonding lines BW3, BW4, BW6, and BW7. The pads 81a, 81b, 81c, and 81d of the light-receiving element are electrically connected to the pads 81g, 81h, 81k, and 81l of MOSFETs 70 and 71 via bonding lines BW3, BW4, BW6, and BW7.

[0029] MOSFET70 (source) and MOSFET71 (source) are electrically connected via bonding line BW5 connecting pads 81i and 81j, respectively.

[0030] Figure 3 This is a schematic diagram of the optical relay in the first embodiment.

[0031] The light-receiving element 50 may also include a control circuit 50a. The control circuit 50a is connected to the first electrode and the second electrode of the photodiode array 50b, respectively. With this configuration, voltage can be supplied to each gate of the MOSFET 70 that is connected to a common source. In addition, the control circuit 50a includes resistors, etc., which can discharge the MOSFET 70 when it switches from on to off, thereby shortening the fall time.

[0032] MOSFETs 70 and 71, for example, can be configured as n-channel enhancement-mode. Figure 3 In this configuration, the gate G of MOSFET 70 is connected to the anode of photodiode array 50b. Furthermore, each source S is connected to the cathode of photodiode 50b, and each drain D is connected to output terminals 31 and 32.

[0033] When the optical signal is on, MOSFETs 70 and 71 are both turned on and connected to an external circuit containing a power supply and load via output terminals 31 and 32. On the other hand, when the optical signal is off, MOSFETs 70 and 71 are both turned off and disconnected from the external circuit. If a common-source connection is used, linear output can be achieved, making high-frequency signal switching easier.

[0034] Two MOSFETs 70 and 71 are connected via a common source, supplying a high-frequency signal to the load when turned on. For example, increasing the number of junction lines connecting the two source electrodes S to two or more reduces the source inductance. Furthermore, making the two or more junction lines non-parallel further reduces the source inductance. Moreover, making the diameter of the junction lines on the MOSFET 70 and 71 side larger than the diameter of the junction lines on the light-emitting element 60 side reduces the line inductance. As a result, transmission losses are reduced.

[0035] Figure 4 This is an example of a circuit for measuring transmission loss. For instance, when a light-emitting element such as an LED is turned on according to an input electrical signal, the MOSFET is turned on, and a high-frequency signal flows from the high-frequency signal source 101 to the load 120. In the case of a vertically oriented MOSFET, the back side of the chip can be the drain electrode. Therefore, a parasitic (stray) capacitance Cst is generated between the proximal MOSFET and the ground electrode.

[0036] The output terminals 31 and 32 of the opto-relay are equivalent to the terminals of the relay. Its transmission loss refers to the insertion loss when the relay is turned on. For example, if the input power is set to P1 and the output power to P2, the transmission loss is expressed by the following formula.

[0037] Transmission loss (dB) = -10log(P2 / P1)

[0038] Figure 5 This is a graph representing the high-frequency transmission characteristics of an opto-relay relative to frequency.

[0039] The vertical axis represents insertion loss (dB), and the horizontal axis represents frequency (Hz). The solid line represents the high-frequency transmission characteristics of the opto-relay with a 25μm thick polyimide substrate 10. The dashed line represents the high-frequency transmission characteristics of the opto-relay using a 400μm thick glass epoxy board instead of the polyimide substrate 10. Insertion loss is based on the transmission characteristics at 10MHz. Around 10GHz, there is no significant difference between the opto-relay using the polyimide substrate 10 and the one using the glass epoxy board. However, the opto-relay using the glass epoxy board exhibits a relatively large loss of approximately -20dB with a valley around 20GHz, reaching -3dB at approximately 13GHz. On the other hand, when using the polyimide substrate 10, it is observed that the loss increases slowly from 10GHz to 30GHz, exhibiting an extremely excellent high-frequency transmission characteristic with a maximum loss of only -5dB.

[0040] The opto-relay 100 implemented in this way can reduce transmission loss. Therefore, it is possible to measure the high-frequency characteristics of semiconductor devices containing next-generation standard ultra-high-speed DRAM with high accuracy and high speed.

[0041] These opto-relays can be widely used in industrial equipment, including semiconductor testers for inspecting ICs.

[0042] While several embodiments of the invention have been described, these embodiments are provided by way of example and are not intended to limit the scope of the invention. These new embodiments can be implemented in various other ways, and various omissions, substitutions, and modifications can be made without departing from the spirit of the invention. These embodiments and their variations are included in the scope or spirit of the invention, and are included in the scope of the invention as set forth in the claims and its equivalents.

Claims

1. A photorelay comprising: A polyimide substrate having a first surface and a second surface opposite to the first surface, and having a thickness of not less than 10 μm and not more than 120 μm; input terminals on the second side; output terminals on the second surface; a light receiving element on the first surface; A light emitting element on the light receiving element; and a first MOSFET and a second MOSFET on the first surface, The input terminal is electrically connected to the light emitting element via a first bonding wire. The light receiving element is electrically connected to the first MOSFET and the second MOSFET via a second bonding wire. The output terminal is electrically connected to the first MOSFET and the second MOSFET via one or more through-hole wirings, the through-hole wirings are provided on the polyimide substrate and have a diameter of 20 μm or more and 40 μm or less, The first MOSFET and the second MOSFET are connected to a common source, The number of third bonding wires connecting the source of the first MOSFET and the source of the second MOSFET is two or more, The two or more third bonding lines are non-parallel, The diameters of the second bonding wires on the first MOSFET and the second MOSFET sides are larger than the diameter of the first bonding wire on the light emitting element side.

2. The optical relay according to claim 1, wherein: The polyimide substrate includes a plurality of through holes extending from the first surface to the second surface. The through-hole wiring is provided in the plurality of through-holes, and the number of the through-hole wirings is plural.

3. The optical relay according to claim 1, wherein: The polyimide substrate has a thickness of 10 μm or more and 100 μm or less.

4. The optical relay according to claim 1, wherein: The polyimide substrate has a thickness of 10 μm or more and 60 μm or less.

5. The photorelay according to any one of claims 1 to 4, wherein: The high-frequency transmission characteristic between 10GHz and 30GHz is that the loss is within -5dB.

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