JPS61144924A - Semiconductor device - Google Patents

Abstract

PURPOSE:To attain ultrahigh speed optical modulation by integrating a resistor connected in series with a drain electrode of a Schottky gate field effect transistor (TR) and a Schottky barrier diode whose anode is connected to the source of the said TR on a semiconductor substrate in monolithic way so as to turn on/off a light emitting element in high speed. CONSTITUTION:The anode of the Schottky barrier diode 22 is connected to the source of the Schottky gate field effect TR20 and the cathode of the diode 22 is connected to a terminal 24. On the other hand, a terminal of a resistor 26 is connected to the drain of the TR20 and the other terminal of the resistor is connected to a power supply terminal 28. When an input signal pulse to an input terminal 30 is at a low level, that is, at a common potential, the cathode of the diode 22 and the gate of the TR20 are of the same potential and the gate potential of the TR20 is lower than the source potential by a conductive potential difference of 0.7V of the diode 22.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of Industrial Application The present invention relates to a semiconductor device effective in driving a light emitting element that converts an electrical signal into an optical signal in the field of optical communication. If so, the present invention relates to a semiconductor device that can perform ultra-high-speed optical modulation operation on a light emitting element and can be realized as a monolithic integrated circuit.

Conventional Technology Today, there is a very urgent need for higher speeds and higher capacity optical communications, and for this reason, driver circuits for light emitting devices such as light emitting diodes and laser diodes are also required to be even faster. ing. This driver circuit is realized using a monolithic integrated circuit for the following reasons: (1) cost reduction by eliminating assembly steps, (2) miniaturization of the device, and (3) improvement of high-speed and high-frequency characteristics by eliminating parasitic elements. That is ideal. Further, it is desired that this monolithic integrated circuit for the driver circuit can be operated with a single power supply and that it can be easily driven with a normal positive pulse.

FIG. 3 is a circuit diagram showing an example of a driver circuit for a light emitting element such as a light emitting diode or a laser diode, which has been most commonly used in the past.

The circuit shown in FIG. 3 consists of two transistors 1 and 2 whose emitters are commonly coupled to each other, and constitutes a current switching type switch circuit. Briefly, the collector of one transistor 1 is connected to a power supply line via a light emitting element 3 such as a light emitting diode, the collector of the other transistor 2 is connected to the same power supply line, and the emitters connected in common are connected to the power supply line. is connected to the constant current source 4.

The paces of the two transistors are connected to complementary outputs of a complementary driver 7 such that driving pulse signals 5 and 6 having an inverse relation to each other are supplied, and an input signal pulse 8 is connected to an input of the complementary driver 7. applied.

In order to realize a high-speed, large-current switch, a high-speed switching bipolar transistor is used as the transistor 1.2, and this transistor is operated only in a non-saturation region.

Further, as the complementary driver 7, an emitter coupled logic (ECL) circuit that can operate at high speed is usually used.

If we consider driving a light emitting element using the circuit shown in Figure 3,
A semiconductor light emitting device such as a laser diode or a light emitting diode has a parasitic capacitance in parallel with itself. Therefore, when the light emitting device is turned on, charge is accumulated. Therefore, when the transistor connected to the light emitting element is turned off and the light emitting element enters a current cutoff state, the charge stored in the parasitic capacitance of the semiconductor light emitting element is
Discharge. However, since the charge is dissipated only by the self-discharge current path flowing through the light emitting device, the turn-off time cannot be made fast. Therefore, the optical output does not disappear quickly, and a phenomenon of the optical output trailing off occurs.

Further, the circuit shown in FIG. 3 has a differential switch configuration in order to operate the transistors 1.2 at high speed in a non-saturation region, and for this reason, the above-mentioned complementary driver is essential. As this high-speed complementary driver, in many cases, an ECL circuit, which is relatively easy to operate, is used.

However, since it is not possible to directly input the normally used positive pulse signal to the ECL circuit, in reality,
A level conversion circuit is required before the circuit shown in FIG.

Furthermore, it is difficult to operate this type of circuit with a single power supply, as shown in the circuit configuration of FIG.

Problems to be Solved by the Invention As described above, the conventional light emitting device drive circuit with a differential switch structure (1) cannot turn off the light emitting device at a high speed; (2) cannot provide a high speed complementary driver; Further, there were problems such as (3) the inability to directly input a positive pulse signal manually, and (3) the inability to operate with a single power supply. This has been an obstacle to achieving higher performance, smaller size, and lighter weight of transmitter circuits for optical communications, and improvements have been awaited.

In recent years, Schottky gate field effect transistors capable of high-speed operation and large current drive have been put into practical use.
By using the Schottky gate field effect transistor, it is possible to overcome the drawbacks of the circuit of FIG.

FIG. 4 shows an example of a driver circuit using the Schottky gate field effect transistor. A light emitting element 3 such as a light emitting diode or a laser diode is connected in parallel to the drain electrode and source electrode of the Schottky gate field effect transistor 10, and further, the drain electrode is connected to a power supply line via a resistor 12,
The source electrode is grounded. Further, a human signal pulse is applied to the gate electrode of the Schottky gate field effect transistor 10 via a bias circuit including a capacitor 14 and an inductor 16.

As is clear from the circuit configuration of FIG. 4, the circuit is a shunt drive circuit configuration in which a Schottky gate field effect transistor 10 is connected in parallel with the light emitting element 3.

Therefore, Schottky gate field effect transistor 10
When the light emitting element is placed in a conductive state, both ends of the light emitting element are shorted, so that the light emitting element is not driven. On the other hand, when the Schottky gate field effect transistor IO is placed in a non-conducting state, a voltage difference is generated across the light emitting element, and as a result, the light emitting element is driven.

As described above, when a driver circuit for a light emitting device is configured using a Schottky gate field effect transistor, the Schottky gate field effect transistor is a majority carrier device and carrier accumulation does not occur even during large amplitude operation. There is no need to make the switch a differential circuit.

Furthermore, in the shunt drive circuit, when the current of the light emitting element 3 is cut off, the charge accumulated in the light emitting element 3 is discharged through the Schottky gate field effect transistor 10, so the turn-off time can be significantly improved, and ultra-high speed operation can be achieved. optical modulation becomes possible.

However, Schottky gate field effect transistors capable of driving large currents are usually normally on type, that is, depletion type, and it is necessary to apply a negative potential to the gate electrode in order to cut off the drain current.

For this reason, in a driver circuit using a Schottky gate field effect transistor, it is necessary to input a signal through a bias circuit that provides a gate bias, such as a capacitor 14 and an inductor 16.

Therefore, it can be said that the circuit of FIG. 4 normally requires two power supplies.

Furthermore, in a wideband optical communication system, in order to satisfy low-pass characteristics, the actance element of the bias circuit described above becomes large in size, and this often causes deterioration of high-pass characteristics.

Furthermore, it is practically impossible to realize the circuit of FIG. 4 as a monolithic integrated circuit because the additional circuitry called the bias circuit requires a large amount of current.

In this way, even if a Schottky gate field effect transistor is used, (1) it cannot be driven by directly inputting a positive pulse, and (2) an additional circuit called a bias circuit that requires a large value of reactance is required. Therefore, there were problems such as the inability to form a monolithic integrated circuit and (3) inability to operate with a single power supply. Therefore, in this case as well, it has not been possible to achieve higher performance, smaller size, and lighter weight of the transmitting circuit for optical communication.

Therefore, the present invention solves the above-mentioned problems and (1) can drive the positive pulse directly by hand, (2) has a simple configuration without requiring any additional circuits, and (3) has a single It is an object of the present invention to provide a monolithic integrated circuit semiconductor device that can be operated using a power source and can be applied to high-speed driving of light emitting elements.

According to the invention, a Schottky gate field effect transistor, a resistor connected in series with the drain electrode of the Schottky gate field effect transistor, and a Schottky gate field effect transistor are provided. A semiconductor device is provided, characterized in that a Schottky barrier diode whose anode is connected to a source electrode of a transistor is monolithically integrated and formed on a semiconductor substrate.

In a semiconductor device such as the above, the anode of the Schottky barrier diode is connected to the source electrode of the Schottky gate field effect transistor, so the cathode of the Schottky barrier diode and the gate electrode of the Schottky gate field effect transistor are connected to each other. When both are set to the same potential, the gate electrode of the Schottky gate field effect transistor becomes more negative in potential than the source electrode by the forward potential difference of the Schottky barrier diode. Therefore, the Schottky gate field effect transistor can be placed in a reliable non-conducting state in both depletion mode and enhancement mode. On the other hand, simply applying a positive pulse to the gate electrode of a Schottky gate field effect transistor turns the Schottky gate field effect transistor into a conductive state. Therefore, it can be operated with a single power supply.

Thus, when both ends of the light emitting element are connected between the drain electrode and the source electrode of the Schottky gate field effect transistor and the light emitting element is driven in a shunt driver circuit format, a positive voltage is applied to the gate electrode of the Schottky gate field effect transistor. By simply applying a pulse, the light emitting element can be turned on and off reliably and at high speed.

As a characteristic of the Schottky gate field effect transistor, the charge accumulated in the light emitting element can be discharged through the Schottky gate field effect transistor, making it possible to significantly improve the turn-off time and enable ultra-high-speed optical modulation. can be realized.

Hereinafter, one example of a semiconductor device according to the present invention will be explained with reference to the accompanying drawings.
An example will be explained.

FIG. 1 is a schematic diagram of a semiconductor device of the present invention, in which all of the circuit elements shown are integrated on the same semiconductor substrate to form a monolithic integrated circuit.

In FIG. 1, reference number 20 is a Schottky gate field effect transistor, the source electrode of which is connected to the anode of a Schottky barrier diode 22, and the cathode of the Schottky barrier diode 22 connected to a terminal 24. has been done.

On the other hand, one end of a resistor 26 is connected to the drain electrode of the Schottky gate field effect transistor 20, and the other end of the resistor is connected to a power supply terminal 28.

A gate electrode of the Schottky gate field effect transistor is connected to an input terminal 30, and a drain electrode and a source electrode are connected to load terminals 32 and 34, respectively.

FIG. 2 is a circuit diagram showing an example in which the semiconductor device shown in FIG. 3 described above is used as a driver circuit for a light emitting element. Both ends of a light emitting device 36, such as a light emitting diode or LED diode, are connected to load terminals 32 and 34, power terminal 28 is connected to a positive power source 38, and terminal 24 is grounded. The positive pulse signal is then applied to the input terminal 30.

The forward conduction potential difference of a Schottky barrier diode is
Usually, it is around 0.7■. Therefore, the threshold voltage v of the Schottky gate field effect transistor 20
It is created so that th is about -0.5■. Therefore, a depletion type Schottky gate field effect transistor that can be driven with a large current can be obtained.

In the above configuration, when the human input signal pulse to the input terminal 30 is at a low level, that is, at ground potential, the cathode of the Schottky barrier diode 220 and the gate electrode of the Schottky gate field effect transistor 20 are at the same potential, and the Schottky gate field effect transistor 20 has the same potential. The gate electrode potential of the Schottky gate field effect transistor 20 is lower than the source electrode potential by the conduction potential difference of the key barrier diode of 0.7 . Therefore, the potential of the gate electrode of the Schottky gate field effect transistor 20 with respect to the source electrode is 10,7■ which is even lower than the threshold voltage -0,5■ of the Schottky gate field effect transistor 20, and the Schottky gate electric field The effect transistor is placed in a positive non-conducting state. As a result, the light emitting element 30 is driven and emits light.

On the other hand, the input signal pulse to the input terminal 30 becomes high level, and the Schottky gate field effect transistor 20
When the gate electrode potential becomes a positive potential or a negative potential whose absolute value is less than 0.5 .mu.m with respect to the source electrode potential, the Schottky gate field effect transistor becomes conductive. As a result, the voltage between the terminals of the light emitting element 36 becomes zero,
Further, the charge accumulated in the light emitting element 36 is quickly discharged via the Schottky barrier diode 20, and the charge accumulated in the light emitting element 36 is quickly discharged through the Schottky barrier diode 20.
quenches rapidly.

Thus, by simply applying a positive pulse to the input 30, the Schottky gate field effect transistor 20 can be turned on and off, and the light emitting device 36 can be turned on and off reliably and at high speed. Since the positive pulse applied to the input 30 is only concerned with the potential with respect to the ground terminal 24, the above circuit can be used normally without requiring an additional circuit for the input of the circuit. It can be operated from a single power supply by matching the pulse signal that is available. Furthermore, since elements with high reactance are not required, it is easy to form a monolithic integrated circuit, and the circuit can be made smaller and lighter.

Note that when the threshold voltage vth of the Schottky gate field effect transistor 20 is less than -0.7■, there is only one Schottky barrier diode 22, and when the human power 30 is at ground potential, the Schottky gate electric field The effect transistor 20 can be reliably placed in a non-conductive state. However, if the threshold voltage vth of the Schottky gate field effect transistor 20 is deeper than -0.7mm, two or more Schottky barrier diodes 22 are connected to the same transistor so that a larger bias can be realized by the threshold voltage. Connect in series in the direction.

Furthermore, when current drive capability is required, two or more Schottky barrier diodes 22 are connected in series,
This can be achieved by making the threshold voltage vth of the Schottky gate field effect transistor 20 even more negative.

Note that instead of the Schottky barrier diode 22,
Although it is possible to use a junction diode, in consideration of the junction capacitance of the diode, a Schottky barrier diode is preferable in order to quickly turn on and off the Schottky gate field effect transistor.

Effects of the Invention As is clear from the above description, the semiconductor device according to the present invention is capable of ultra-high-speed optical modulation operation by turning on and off light-emitting elements such as light-emitting diodes and laser diodes at high speed.

Furthermore, the semiconductor device of the present invention operates with a single power supply, can be matched with normally used positive pulse signals without any additional circuitry, and does not require elements with large actance, so it can easily be used as a monolithic integrated circuit. It can be made smaller and lighter. The monolithic integrated circuit realizing the semiconductor device according to the present invention does not have any special elements and is composed only of a Schottky gate field effect transistor, a Schottky barrier diode, and a resistor.
It can be easily produced with good yield in a normal manufacturing process.

[Brief explanation of drawings]

FIG. 1 is a circuit diagram of one embodiment of a semiconductor device according to the present invention. FIG. 2 is a circuit diagram showing an example in which the semiconductor device according to the invention shown in FIG. 1 is used as a light emitting element driver circuit. FIG. 3 is a circuit diagram showing an example of a conventional light emitting element drive circuit. FIG. 4 is a circuit diagram showing an example of a light emitting device driving circuit using a Schottky gate field effect transistor. [Main reference numbers] 1.2...transistor, 3...light emitting element, 4...constant current source, 7...complementary driver, 10...Schottky gate field effect transistor, 1
2...Resistor, 14...Capacitor, 16...Inductor,

Claims (2)

[Claims] (1) A Schottky gate field effect transistor, a resistor connected in series to the drain electrode of the Schottky gate field effect transistor, and a Schottky barrier diode whose anode is connected to the source electrode of the Schottky gate field effect transistor. What is claimed is: 1. A semiconductor device characterized in that these are monolithically integrated and formed on a semiconductor substrate. (2) The semiconductor device according to claim (1), wherein the Schottky gate field effect transistor is a depression type. (3) The Schottky barrier diode is one or more Schottky barrier diodes connected in series in the same direction.
The semiconductor device according to item 1) or item (2).