JP2000216485A - Semiconductor device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To form a semiconductor device which is proper for laser diode driving by a harmonic superposition method. SOLUTION: After an output signal from an oscillator is amplified by an output amplifier, it is applied to a laser diode. A transistor element and a passive element for constituting an oscillator and an output amplifier are integrated on the same silicon semiconductor substrate. The semiconductor chip 50 is fixed on an island 51 and is connected to each lead by a bonding wire 64. An extension part 58 which is continuous to the island 51 is provided and is extended between lead terminals 60, 61. A ground potential GND is given to the extension part 58.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a semiconductor device in which an oscillation circuit for driving a laser element by a high frequency superposition method is integrated.

[0002]

2. Description of the Related Art In recent years, optical disk technology has been remarkably developed. An optical disc can be read out of a recording medium in a non-contact manner by using a laser beam. The CD as a representative is now widely accepted in the market because of its small size and high-speed accessibility. Under such circumstances, DVD (digital video disc) has appeared. DVD technology has many parts in common with CD technology, such as the use of laser light and the same disk size.

On the other hand, DVDs have a storage capacity (4.
7 GB) has an advantage that the storage capacity of CD audio is approximately six times (740 MB), and by utilizing this advantage, for example, an application for storing compressed image data corresponding to one movie on one disc Is attracting attention. Further, taking advantage of the large capacity, the use as an external storage device in a personal computer has been developed.

[0004] One of the factors for achieving such a large capacity of DVD is that the track pitch of a disk is made narrower than that of a CD. Reducing the track pitch means reducing the size of each pit itself, and at the same time, narrowing down the spot of the laser beam to be applied to the pits.

Therefore, a DVD player is configured so that the laser beam has a shorter wavelength than that of a CD, so that the focal point of the laser beam on the disk surface becomes smaller. Note that D
The wavelength of the laser light for VD is 635/650 nm and that for CD is 780 nm.

FIG. 5 shows a conventional AP for driving a laser element.
This is a C (auto power control) circuit, and the laser light output from the laser diode LD is not only irradiated onto the DVD but also received by the photodiode PD. Light is converted into an electric signal by the photodiode PD, and at this time, an electric signal corresponding to the amount of laser light is obtained. The APC circuit is controlled in accordance with the electric signal so that the light amount of the emitted laser light becomes constant.

There are two types of laser diode light emission modes: a single mode that emits light at a single wavelength as shown in FIG. 6A, and a multimode that emits light at a plurality of wavelengths as shown in FIG. 6B. Therefore, a multi-mode laser diode is used for various reasons. 780 nm
For CD applications using a wavelength of 650 nm, a corresponding laser diode has been developed and supplied stably.
For / 650 nm DVD applications, a laser diode that emits light in multi-mode still has disadvantages such as low reliability and high cost.

Therefore, conventionally, a multi-mode laser beam has been obtained by driving a single-mode laser diode by a high-frequency superposition method. In the high frequency superposition method, FIG.
(A) A laser diode capable of emitting short-wavelength laser light (single mode) emits light in a multi-mode at the start of operation. In particular, if the laser diode is a self-pulsation type, it tends to be in a multi-mode at the time of rising. As a circuit for achieving the harmonic superposition method, an oscillator OSC for applying a high-frequency signal to the laser diode LD is provided as shown in FIG. A rising state is continued by applying a high-frequency signal to the laser diode from the outside, and laser light including a plurality of wavelengths is emitted. Thus, by using the harmonic superposition method, it is possible to use a single-mode laser diode and look as if using a multi-mode laser diode. A laser diode that emits 650 nm laser light in a single mode is widely available on the market as a general-purpose product, and the harmonic superposition method is one of the effective means at present.

[0009]

However, conventionally, since the output signal of the oscillator is directly applied to the laser diode, the oscillation frequency and the transmission output tend to change depending on the load impedance of the diode. That is,
For example, when a filter circuit is provided on the user side to remove a harmonic component of the oscillator, there is a disadvantage that the oscillation frequency and the oscillation output are easily changed by the influence of the filter circuit.

Conventionally, an oscillation circuit is conventionally composed of a GaAs discrete product, and there has been an increasing demand for making such a circuit an MMIC (monolithic / microwave integrated circuit) in order to reduce the cost of the product. .

[0011]

SUMMARY OF THE INVENTION The present invention has been made in view of the above-mentioned problems, and is a semiconductor device having a built-in oscillation circuit for driving a laser element by a high-frequency superposition method, comprising an oscillator and an output of the oscillator. An output amplifier for outputting an oscillation signal to a laser element and an output terminal of the amplifier are integrated on the same semiconductor chip, the semiconductor chip is mounted on an island of a lead frame, and the external terminal and the first power supply terminal are provided. And the output terminals are electrically connected to corresponding lead terminals, respectively, and an electrode to which a ground potential is applied is extended between the external terminal and the output terminal, including the semiconductor chip. The main part of the lead frame is sealed.

[0012]

Embodiments of the present invention will be described below.

FIG. 1 is a diagram showing an embodiment of the present invention. Reference numeral 1 denotes an oscillator that oscillates at an oscillation frequency corresponding to the resonance frequency of a resonance element LC and outputs an oscillation signal. Output amplifier. The oscillator 1 and the output amplifier 2 are configured to be integrated on the same semiconductor substrate.

In FIG. 1, an oscillator 1 includes a resonance element LC
Oscillates at several hundred MHz according to the resonance frequency of An oscillation signal from the oscillator 1 is amplified by the output amplifier circuit 2. The output amplified signal of the output amplifier circuit 2 is subjected to DC removal by the coupling capacitor C. The output signal after DC removal is
After being superimposed on the bias from the APC circuit, it is applied to the laser diode LD. The relationship between the laser diode LD and the oscillation amplification signal is as shown in FIG. 7, and the bias coincides with the oscillation start current of the self-oscillation type single mode laser diode LD. The laser diode LD oscillates by the oscillation signal on which the bias is superimposed. When the amplitude is positive, the laser diode LD is turned on, and when the amplitude is negative, the laser diode LD is turned off. Therefore, laser light is emitted from the laser diode LD every unit time.

As described above, the laser diode LD rises every unit time, so that the single mode type laser diode LD emits laser light in a multi-mode, that is, including a plurality of wavelengths. Since the laser diode LD is turned on at a high frequency of several hundred MHz, it looks as if the laser diode LD emits light continuously. Therefore, it appears that the laser diode LD oscillates in multi-mode.

FIG. 2 shows the oscillator 1 and the output amplifier circuit 2 of FIG.
3 is a diagram showing a specific circuit example of FIG. The oscillator 1 is a Colpitts type oscillator, and includes a transistor Tr1 having an external terminal LC connected to a base, and two transistors Tr1 connected in series between the base of the transistor Tr1 and a grounded ground terminal (second power supply terminal GND). It comprises capacitors C1 and C2, and the connection point between the capacitors C1 and C2 is connected to the transistor Tr1
1 base. Since the Colpitts oscillator is a well-known circuit, the description of its operation is omitted.

The output amplifier 2 includes a transistor Tr2 to which an oscillation signal is applied to a base, and a transistor Tr2.
The resistors R2 and R3 set the base bias of R2. Note that the resistor R2 also serves as a feedback resistor. The oscillation signal from the oscillator 1 is applied to the base of the transistor Tr2 and is amplified by the current amplification factor β2. The amplified signal is generated at the collector of the transistor Tr2,
The collector current of r2 is supplied to the laser diode LD (not shown) via the output terminal OUT. These oscillator 1 and output amplifier circuit 2 have a first power supply terminal VCC.
And a power supply potential such as + 5V.

The collector current of the transistor Tr2 is fed back via the resistor R2. Since the base current and the collector current of the transistor Tr2 are in opposite phase relation to each other, a negative feedback loop is performed. The input impedance of the output amplifier 2 increases due to the negative feedback loop. In general,
Although the input impedance of the BIP transistor is low,
The input impedance of the output amplifier 2 is increased by applying negative feedback.

The output impedance of the oscillator 1 is as high as several hundred Ω, and the load of the laser diode LD is as low as several Ω. In general, the input / output impedance of the output amplifier 2 used in a high frequency band of several hundred MHz is set low. However, by setting the input / output impedance of the output amplifier 2 of the present invention to several hundreds Ω and several tens Ω, respectively. The impedance of the oscillator 1 and the laser diode LD can be matched.

FIG. 3 is a cross-sectional view showing an integrated circuit device embodying the above circuit configuration, in which a transistor element TR, a capacitance element C, and a resistance element R are formed on the same substrate. In the figure, reference numeral 11 denotes a P-type silicon semiconductor substrate. 13 is an N + type buried layer, 14 is a P + type isolation region, 18 is an N + type collector low resistance region of the transistor element TR, and 19 is an N + type lower electrode area of the capacitor element C.
Reference numeral 20 denotes a LOCOS oxide film for element isolation. Substrate 11
An N-type epitaxial layer formed thereon by a vapor deposition method is separated by a P + isolation region 14 and a LOCOS oxide film 20, and the transistor element TR is formed in the isolated region.
And the capacitor C are formed.

The resistance element R is formed by forming a polysilicon resistor 25 on the LOCOS oxide film 20 by a technique of forming a polysilicon layer, doping impurities (phosphorus), and photoetching. The polysilicon resistor 25 is formed with a constant line width and a length at which a desired resistance value is obtained. The upper portion of the polysilicon resistor 25 is covered with an insulating layer 28, and electrodes 44 and 45 are formed. This polysilicon resistor 25 constitutes the resistors R1 to R6 of FIG. 2 in the circuit diagram.

In the transistor element C, a P-type base region 23 is formed in the element-isolated region, emitter and base contact holes are formed, and a phosphorus-doped polysilicon layer is deposited on the emitter contact hole. The diffusion source film 31 is formed by selectively ion-implanting boron into the base contact hole and performing emitter diffusion. Since the emitter diffusion is solid-phase diffusion from the polysilicon layer, an extremely shallow junction can be formed on the surface of the base region 23, whereby a transistor element TR for high frequency use can be configured. The electrode 32 is a polysilicon layer and the electrodes 38, 39, 4
0 and 41 are aluminum layers. This transistor element TR is equivalent to the transistors TR1 and TR in FIG.
Constituting No. 2.

In the capacitive element C, a lower electrode region 19 is provided in a region where the element is isolated, a part of the surface is opened, a dielectric thin film 27 such as a silicon nitride film is formed, and an upper electrode is formed thereon. This is one in which electrodes 34 and 43 are formed. The lower electrode region 19 is taken out by the electrodes 33 and 42.
The electrodes 33 and 34 are a polysilicon layer, the electrodes 42 and 4
3 is an aluminum layer. This capacitance element constitutes the capacitances C1 to C4 in FIG. 2 in the circuit diagram.

These electrodes 38 to 45 extend on the surface of the semiconductor chip and electrically connect each circuit element to form a circuit network. Further, the polysilicon layers 32, 33 and 34 can be formed simultaneously with the diffusion source film 31. Further, when the upper portion of the polysilicon resistor 25 is covered with the silicon nitride film of the dielectric thin film 27, the polysilicon resistor 25
Resistance value fluctuation can be prevented.

FIG. 4 is a view showing a state in which the semiconductor chip 50 on which such a circuit / element is formed is mounted on a lead frame. The semiconductor chip 50 is fixed on the island 51 of the lead frame so as to be electrically connected to the semiconductor substrate 11. On the surface of the semiconductor chip 50, the external terminal LC and the output terminal of the circuit diagram of FIG. OUT,
Electrode pads 52, 53, 54, and 55 respectively corresponding to the first power supply terminal VCC and the second power supply terminal GND are provided. From the island 51, two lead terminals 56, 57 and two extending portions 58, 59 are continuous in a cross shape, and furthermore, four independent lead terminals 60, 6
1, 62 and 63 are arranged.

The lead terminals 60, 61, and 62 are connected to the electrode pads 52, 53, and 54 by bonding wires 64, and are connected to an external terminal LC, an output terminal OUT, a first power supply terminal VCC, and a second power supply terminal GND. And the external connection lead terminal corresponding to. Lead terminal 63 is not connected NC
And Further, a bonding wire 64 is struck from the electrode pad 55 to the extending portion 58. This allows
The extension portion 58 is provided with a shielding function, and the external connection terminal LC is provided.
Lead terminal 60 for output and lead terminal 6 for output terminal OUT
1 is separated from the capacitive coupling. The lead terminal 56 also has a function of separating the capacitive coupling between the lead terminal 61 and the lead terminal 62.

Then, the main part is transfer-molded with the thermosetting resin 65 so that the leading ends of the lead terminals 57, 58, 60 to 63 including the semiconductor chip are led out.

[0028]

As described above, according to the present invention, the provision of the oscillator 1 and the output amplifier circuit 2 enables
This has the advantage that a stable transmission circuit can be provided regardless of the connected load.

Further, since the oscillator 1, the output amplifier circuit 2, and each passive element are integrated on a silicon substrate, it is possible to greatly reduce the cost.

Further, by providing the extending portion 58 between the connection terminal LC of the resonance circuit and the output terminal OUT, the capacitive coupling between the two can be separated.

[Brief description of the drawings]

FIG. 1 is a circuit diagram for explaining the present invention.

FIG. 2 is a circuit diagram for explaining the present invention.

FIG. 3 is a cross-sectional view for explaining the present invention.

FIG. 4 is a plan view for explaining the present invention.

FIG. 5 is a circuit diagram for explaining a conventional example.

FIG. 6 is a diagram for explaining a laser emission mode.

FIG. 7 is a circuit diagram for explaining a harmonic superposition method.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Oscillator 2 Output amplifier circuit 50 Semiconductor chip 51 Island 58 Extension part

 ──────────────────────────────────────────────────続 き Continuing on the front page (72) Inventor Masaaki Nakatani 2-5-5 Keihanhondori, Moriguchi-shi, Osaka Sanyo Electric Co., Ltd. (72) Inventor Yoshiaki Matsumiya 2-chome, Keihanhondori, Moriguchi-shi, Osaka No. 5 Sanyo Electric Co., Ltd. (72) Inventor Shigeo Kimura 2-5-5 Keihanhondori, Moriguchi-shi, Osaka F-term in Sanyo Electric Co., Ltd. 5F073 AB14 BA06 FA28 FA29 GA12 5F082 AA40 BA04 BC03 BC13 BC18 EA04 FA13 FA18 5J081 AA03 BB02 CC06 CC10 CC43 DD03 EE02 EE03 FF17 FF23 JJ12 MM01 MM07

Claims (2)

[Claims] 1. A semiconductor device having a built-in oscillation circuit for driving a laser element by a high frequency superposition method, comprising: an oscillator; an output amplifier for outputting an output oscillation signal of the oscillator to the laser element; and an output of the amplifier. Terminals are integrated on the same semiconductor chip, the semiconductor chip is mounted on an island of a lead frame, and the external terminal, the first power supply terminal, and the output terminal are electrically connected to corresponding lead terminals. Connecting, extending an electrode to which a ground potential is applied between the external terminal and the output terminal, and sealing a main part of the lead frame including the semiconductor chip. , Semiconductor devices. 2. The semiconductor device according to claim 1, wherein the electrode to which the ground potential is applied extends from the island.