JPH0479174B2 - - Google Patents

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention converts an input signal into an optical signal using a light emitting element, and converts the optical signal into an electrical signal using a photovoltaic diode array optically coupled to the light emitting element. The present invention relates to a solid state relay using optical coupling, which uses the electrical signal to drive an output metal oxide semiconductor field effect transistor (MOSFET) to obtain an output contact signal.

[Prior art] Figure 6 shows a conventional solid state relay (patent application No. 61-255022).
This is a circuit diagram of Between input terminals 6 and 6',
A light emitting diode 1 is connected. The photovoltaic diode array 2 is optically coupled to the light emitting diodes 1 . When an input current flows between the input terminals 6 and 6', the light emitting diode 1 generates an optical signal, which generates a photovoltaic force across the photovoltaic diode array 2.

The drain and source of an insulated gate field effect transistor 3 (hereinafter referred to as "MOSFET 3") are connected between the output terminals 7 and 7, respectively. The substrate of this MOSFET 3 is commonly connected to the source. The photovoltaic diode array 2
The photovoltaic force generated across the is applied between the gate and source of the output MOSFET 3 via the impedance element 4, and at the same time is applied to the normally-on static induction transistor (SIT) or field effect transistor. The signal flows through the driving transistor 5 made of (FET). Therefore,
A current that charges the gate capacitance of MOSFET 3 and a current that flows through drive transistor 5 flow through impedance element 4 . Therefore, due to the voltage drop across the impedance element 4, a bias voltage of the polarity shown is applied between the gate and source of the driving transistor 5. This bias voltage instantly puts the driving transistor 5 into a high impedance state. Therefore, due to the presence of the driving transistor 5, the gate of the output MOSFET 3
There is no delay in charging operations between sources. When the output MOSFET 3 is in the enhancement mode, the impedance state between the drain and source changes from a high impedance state to a low impedance state as the voltage between the gate and source increases. Therefore, when an input current flows between input terminals 6 and 6' of the relay, output terminal 7
-7' changes from the OFF state to the ON state, and has no mechanical moving parts and functions in the same way as an electromechanical relay.

When the input current between input terminals 6-6' is cut off,
The charge accumulated in the gate capacitance of the MOSFET 3 is discharged via the driving transistor 5.
At this time, since the bias voltage is not applied between the gate and source of the driving transistor 5, the driving transistor 5 is in an on state, and therefore, this discharging operation is completed in an extremely short time.

[Problems to be Solved by the Invention] In the above-mentioned prior art, when the input current is flowing steadily between the input terminals 6 and 6', a small amount of current flows through the drive transistor 5 and the impedance element 4. As a result, a bias voltage is applied between the gate and source of the driving transistor 5 to maintain a high impedance state. At this time, the voltage value V ₄ applied to the impedance element 4 is
It is determined depending on the cutoff characteristics of the driving transistor 5 and the value of the impedance element 4. If the cutoff characteristics of the driving transistor 5 are constant, the bypass loss of photovoltaic power (that is, the amount consumed via the driving transistor 5 without being supplied between the gate and source of the output MOSFET 3) can be reduced. teeth,
It is better to set the impedance element 4 to a value as large as possible. In other words, if the impedance element 4 has a large value, the relay can be operated impressively even if the input current between the input terminals 6 and 6' is small. However, if the resistance value of the impedance element 4 is too large, the current that charges the capacitance between the gate and source of the output MOSFET 3 (current for increasing the gate potential of the MOSFET 3) also flows through the impedance element 4. , which imposes a limit on this current value. In other words,
Output terminal 7-7' for input current rise
In order to increase the response speed of the impedance change between the two, the value of the impedance element 4 must be small.

In this way, in the above-mentioned conventional technology, in order to reduce the minimum input current required to operate the relay, that is, the impression current (I _F on),
It is necessary to set the value of impedance element 4 to a large value, and it is also necessary to set the value of impedance element 4 to a large value.
In order to shorten the response time Ton until -7' turns ON, it is necessary to set the value of impedance element 4 small.

The present invention has been made in view of these points, and its purpose is to provide a solid state relay with a simple structure that has a small impressed current and a fast response speed.

[Means for Solving the Problems] In the present invention, in order to solve the above problems, as shown in the attached drawings, a light emitting diode 1 such as a light emitting diode 1 that generates an optical signal in response to an input signal is used. a photovoltaic diode array 2 that receives the optical signal and generates photovoltaic force; an impedance element 4 connected in series with the photovoltaic diode array 2; 4 is applied between the gate and the substrate,
A pair of current-carrying electrodes are connected between the output MOSFET 3 that changes from the first impedance state to the second impedance state and the gate and substrate of the output MOSFET 3, and the connection between the impedance element 4 and the photovoltaic diode array 2. a normally-on drive transistor 5 which is biased into a high impedance state by the voltage generated across the impedance element 4 when the photovoltaic diode array 2 generates a photovoltaic force; In the solid-state relay comprising
The impurity semiconductor region 44 is made up of the resistance of the diffusion region 40 in which impurities of different conductivity types are diffused into the impurity semiconductor region 44 so that the PN junction formed between the impurity semiconductor region 44 and the diffusion region 40 is reverse biased when a photovoltaic force is generated. One end of the diffusion region 40 (aluminum electrode 4
2), the diffusion region 40 is formed in a meandering manner at a predetermined interval, and the meandering interval of the diffusion region 40 is such that the diffusion region 40 and The spacing is set such that the depletion layers formed between the impurity semiconductor regions 44 are connected, and the aluminum film 49 is deposited to cover the diffusion regions.

[Operation] The operation of the present invention will be explained with reference to FIGS. 3a and 3b.
When a photovoltaic force is generated, a current due to the photovoltaic force flows through the impedance element 4, and the PN junction between the diffusion region 40 and the impurity semiconductor region 44 is placed in a reverse bias state. Since the impurity concentration of the impurity semiconductor region 44 is low, even if the applied voltage is low, the depletion layer is formed in the impurity semiconductor region 44 as shown by the broken line in FIG.
It expands greatly on the side of . Moreover, since the aluminum film 49 for the purpose of shielding light is present on the diffusion region 40, this aluminum film 49 acts as an electric field applying film and further expands the depletion layer. When the reverse bias voltage exceeds a predetermined value, as shown by the broken line in FIG. 3b, the impurity semiconductor region 4
4, the depletion layers become connected, resulting in a state in which electrons can flow, as shown by the arrows in the figure. Therefore, current flows through the meandering diffusion region 40 without meandering, and the resistance value of the impedance element 4 decreases. Therefore, in the present invention, the low resistance value of the impedance element 4 decreases during a transient period when an input signal is generated, and the gate-source capacitance of the output MOSFET 3 can be rapidly charged. Also, when the input signal is stable and steady, the third
As shown in Figure a, since the depletion layer does not reach a connected state, a high resistance is obtained by the meandering diffusion region 40, and a small input signal biases the normally-on drive transistor 5 to a high impedance state. It is something that can be done.

[Example] In the illustrated example, a photovoltaic diode array 2 is used in a solid state relay having the configuration shown in FIG.
The impedance element 4 and driving transistor 5 are formed on a single-chip dielectric isolation substrate. FIG. 1 is a perspective view of the impedance element 4 portion of this dielectric isolation substrate, and FIG. 2 is a sectional view taken along line A-A' in FIG. 1. The dielectric isolation substrate is a substrate in which a plurality of single crystal silicon regions exist like islands on a polycrystalline silicon substrate 46 surrounded by an insulating film 45 such as SiO ₂ . In this embodiment, impedance element 4
An impurity semiconductor region 44 is formed by doping an N-type impurity at a low concentration into a single crystal silicon region in which a single crystal silicon region is formed. Furthermore, a diffusion region 40 in which P-type impurities are diffused at a high concentration is formed on the surface. As shown in FIG. 1, this diffusion region 40 is formed in a meandering manner. Since the diffusion region 40 has a high impurity concentration, it is a low resistance layer and has a resistivity corresponding to the impurity concentration. The surfaces of the diffusion region 40 and the impurity semiconductor region 44 are covered with an insulating film 47 made of SiO ₂ . Aluminum electrodes 41 and 4 are connected to both ends of the diffusion region 40 in ohmic contact.
2 are connected. Aluminum electrodes 41, 42
The resistance value between them is approximately determined by the resistivity of the diffusion region 40 and the width and length of the diffusion region 40. The impurity concentration of the diffusion region 40 is higher near the surface, and the current density is higher near the surface. Therefore, the depth of the diffusion region 40 has little to do with the resistance value. In the example, the specific resistance of the N-type impurity semiconductor region 44 is 60Ω, the width of the P-type impurity diffusion region 40 is 3 m, the interval is 4 m, and B (boron) is used as the impurity, and the concentration is 2.5. ×
The dose was 10 ¹³ . One aluminum electrode 42
is also in ohmic contact with an impurity semiconductor region 44 in which N-type impurity is diffused at a low concentration. Therefore, the N-type impurity semiconductor region 44 is held at the same stable potential as the source of the driving transistor 5 and the output terminal 7'. Note that an electrode region 43 in which N-type impurities are diffused at a high concentration is formed in a portion where the aluminum electrode 42 and the impurity semiconductor region 44 are in ohmic contact. After forming aluminum electrodes 41 and 42 on the substrate,
A passivation film 48 of about 5000 Å made of SiO ₂ is deposited using the CVD method. In addition, a light-shielding aluminum film 49 is coated on parts other than the photovoltaic diode array 2 in order to prevent leakage current from occurring due to light. however,
In FIG. 1, an aluminum film 49 for light shielding is shown.
The figure shows the state before being coated.

As mentioned above, when a photovoltaic force is generated, a current due to the photovoltaic force flows through the impedance element 4,
Since one aluminum electrode 42 has a higher potential than the other aluminum electrode 41, the diffusion region 4
The PN junction between 0 and the impurity semiconductor region 44 is in a reverse bias state. Since the impurity concentration of the impurity semiconductor region 44 is low, even if the applied voltage is low, the depletion layer largely expands toward the impurity semiconductor region 44 as shown by the broken line in FIG. 3a. Furthermore, the diffusion region 4
By connecting the aluminum film 49 for light shielding purpose existing on the electrode 41 to the electrode 41 on the low voltage side, the field plate effect is strengthened, and it becomes possible to expand the depletion layer at a low applied voltage. When the reverse bias voltage exceeds a predetermined value, the depletion layer is connected in the impurity semiconductor region 44 as shown by the broken line in FIG. 3b, and electrons flow as shown by the arrow in the same figure. You will be in a state where you can get it. Therefore, current flows bypassing the meandering resistance pattern of the diffusion region 40 in the direction of the line A-A', and the resistance value of the impedance element 4 decreases.

FIG. 4 shows the relationship between the voltage applied to the impedance element 4 and the current supplied. In the figure, the relationship between the applied voltage and the conducting current when photovoltaic force is generated is as shown in the first quadrant. increases rapidly. Therefore, if the voltage applied to the impedance element 4 is larger than the predetermined value when the input signal rises and the gate-source capacitance of the output MOSFET 3 is charged,
The current flowing through the impedance element 4 increases significantly, and the gate-source capacitance is rapidly charged.

FIG. 5 shows the change in the voltage applied to the impedance element 4 when the input signal rises. As shown in Figure a, when the input signal rises, the photovoltaic diode array generates photovoltaic force, but until the charging voltage of the gate-source capacitance of output MOSFET 3 rises, the photovoltaic force is not generated. Since most of the voltage is shared by impedance element 4, the voltage applied to impedance element 4 is high. While this applied voltage exceeds the predetermined value, the resistance value of the impedance element 4 decreases and the gate-source capacitance is rapidly charged. For output
When the charging voltage of the gate-source capacitance of MOSFET 3 increases, the voltage shared by impedance element 4 decreases, so the resistance value of impedance element 4 increases, making it possible to generate a large bias voltage with a small current. It becomes like this.

In addition, in the example, output MOSFET 3
Although the example is shown in which the mode is the enhancement mode, the mode may also be the depletion mode.

[Effects of the Invention] As described above, the present invention allows a charging current to flow between the gate and source capacitance of the output MOSFET when the input signal is transient, and when the input signal is stable and steady, the charging current flows between the gate and source of the output MOSFET. As an impedance element that applies a bias voltage to a normally-on drive transistor connected to The impurity semiconductor region is connected to one end of the diffusion region so that the PN junction formed between the regions is biased when a photovoltaic force is generated, and the diffusion region is formed in a meandering manner at a predetermined interval. Spacing is for photovoltaic output
The spacing was set so that the depletion layer generated between the diffusion region and the impurity semiconductor region when charging the MOSFET gate-to-substrate capacitance was connected, and the aluminum film covered the diffusion region, so the configuration of the impedance element was simply changed. With just some ingenuity, a large current can bypass the meandering diffusion region when the input signal is transient, allowing the output signal to flow.
The capacitance between the gate and source of the MOSFET can be rapidly charged, and when the input signal is stable and steady, the meandering diffusion region can provide high resistance. Therefore, it is possible to realize a solid-state relay with high sensitivity and high-speed response.

[Brief explanation of the drawing]

Fig. 1 is a perspective view of an impedance element used in an embodiment of the present invention, Fig. 2 is a sectional view taken along the line A-A' of the same, Fig. 3 a and b are explanatory diagrams of the same, and Fig. 4 5 is a diagram showing voltage-current characteristics same as above, FIG. 5 is an operation waveform diagram of same as above, and FIG. 6 is a circuit diagram of a conventional example. 1 is a light emitting diode, 2 is a photovoltaic diode array, 3 is an output MOSFET, 4 is an impedance element, 5 is a driving transistor, 40 is a diffusion region, 41 and 42 are aluminum electrodes, 44 is an impurity semiconductor region, 49 is a It is an aluminum film.

Claims (1)

[Claims] 1. A light emitting element that generates an optical signal in response to an input signal, a photovoltaic diode array that receives the optical signal and generates a photovoltaic force, and an impedance element connected in series with the photovoltaic diode array. an output MOSFET that changes from a first impedance state to a second impedance state by applying the photovoltaic force between the gate and the substrate via the impedance element;
A pair of current-carrying electrodes are connected between the gate and substrate of
A control electrode is connected to a connection point between the impedance element and the photovoltaic diode array, and is biased into a high impedance state by a voltage generated across the impedance element when the photovoltaic diode array generates a photovoltaic force. Normally
In a solid-state relay comprising an on-type driving transistor, the impedance element is composed of a resistance of a diffusion region in which impurities of different conductivity types are diffused into a low concentration impurity semiconductor region, and a resistance between the impurity semiconductor region and the diffusion region. The impurity semiconductor region is connected to one end of the diffusion region so that the PN junction formed therebetween is reverse biased when photovoltaic force is generated, and the diffusion region is formed to meander at a predetermined interval, and the meandering interval of the diffusion region is for photovoltaic output
The spacing is set so that a depletion layer generated between the diffusion region and the impurity semiconductor region is connected when charging the gate-to-substrate capacitance of the MOSFET, and the aluminum film is deposited to cover the diffusion region. solid state relay.