WO2004059359A1

WO2004059359A1 - To-can package of high speed data communications

Info

Publication number: WO2004059359A1
Application number: PCT/KR2003/002263
Authority: WO
Inventors: Euy-Sik Yoon; Pil-Yeon Ju
Original assignee: Aligned Technologies Inc.
Priority date: 2002-12-27
Filing date: 2003-10-24
Publication date: 2004-07-15
Also published as: AU2003273109A1

Abstract

A to-can package for high speed data communications includes an optical element, a stem containing the optical element, and a transmission line inserted into the stem for electrical connection to the optical element. The stem is made of nonconductive dielectric material capable of metal film patterning.

Description

TO-CAN PACKAGE FOR HIGH SPEED DATA COMMUNICATIONS

TECHNICAL FIELD

The present invention relates to a to-can package, and more particularly to a to-can package having a broad bandwidth wherein Sll and S21 values in S parameters are improved by adopting a ceramic stem and a high frequency transmission line of pattern formed on the surface of the stem instead of adopting typical metal stems and leads.

BACKGROUND ART

A conventional to-can package is illustrated in FIGs. la and lb. As shown in

FIG. la, the to-can package for laser diode (LD) includes a laser diode (LD) 101, a photo diode (PD) 102, a submount 103, a cap 105, a heat sink 107, a metal stem 108, leads 110, a lens 111, a leads bonding pad 112, and wires 113. A reference numeral 104 denotes projection of beam radiated from the laser diode.

Also, as shown in FIG. lb, a conventional to-can package for photo diode (PD) includes a cap 105, a metal stem 108, leads 110, a lens 111, wires 113, a receiver PD 114, and a transimpedance amplifier (TIA) 115.

As shown in FIGs. la and lb, generally, a diode such as the laser diode 101 and the photo diode 102 has chip of a small size of 300 X 300 or 500 X 500 [pXp], and is so brittle since it is made of compound semiconductor composed of HI and V classes, or π and VI class. In addition, the diode is generally mounted in the to-can package and sealed up for the purpose of prevention of deterioration or malfunction due to exposure to moisture and atmosphere.

With the above configuration, an applied electrical data signal travels to the to-can package by the leads 110, to thereby operate the laser diode 101 through the wires 113. The electrical data signal is converted by the laser diode 101 into an optical data signal. The optical date signal emits through the lens 111 of the cap 105, and then enters optical transmission media located out of the to-can package.

To the contrary, in case of the to-can package for photo diode, an optical data signal transmitted by an optical fiber is incident on the to-can package through the lens 111 of the cap 105. The incident optical data signal is converted into an electrical data signal by the receiver PD 114, and then transmitted to an exterior data processing system through the leads 110 connected to the to-can package.

Since the to-can package using the metal stem and the leads as a transmission medium has a small stem bandwidth, it is not suitable for high speed data communications requiring high bandwidth over a level of GHz.

FIG. 2 is an enlarged view showing a metal stem and leads in a conventional to-can package. Here, a reference numeral 201 denotes a parasitic capacitance, 202 denotes a parasitic inductance, 203 denotes low-melting glass, 208 denotes a metal stem, and 210 denotes leads. Referring to FIG. 2, there exists a gap between the leads 210 and the metal stem

208 in the to-can package for electrical insulation, that is sealed by the low melting glass

203.

On the other hand, electrical signal transmission is affected by a parasitic capacitance 201 caused by the electric field between the metal stem 208 and the leads 210, and a parasitic inductance 202 due to the leads itself. As a result, the metal stem 208 acts as a low pass filter, which restricts bandwidth of signal transmission.

For more detail description, an enlarged view of the metal stem and the leads is shown in FIG. 3a. Here, a reference numeral 301 denotes the metal stem, 302 denotes the low melting glass, and 303 denotes the leads.

As shown in FIG. 3a, one side of the metal stem 301 may be defined as a port 1 and the other side thereof may be defined as a port 2. Here, a signal transmission matrix of the ports 1 and 2 may be represented as S parameter by a scattering matrix. Accordingly, the stem and the leads can be made modeling as a 2-port system by means of S parameter as shown in FIG. 3b. At this time, assuming that the system is symmetrical, a reflection coefficient Sll of a reflection signal to incident signal applied in the port 1 (or port 2) is represented as following equation 1.

Equation 1

Also, a transfer coefficient S12 representing a ratio of signal transmitted to the port 2 (or port 1) shall become equation 2. Equation 2

As shown in FIG. 3c, a parasitic capacitance generated in the low melting glass

302 for sealing the gap between the leads 305 and the stem 304 can be defined as

equation 3.

Equation 3

Here, b/a is ration of a radius of stem hall 304 to a radius of the leads 305.

Also, the parasitic inductance due to the leads is proportional to the length of the

leads. Thus, in case of short leads, the parasitic inductance is so small compared to the

parasitic capacitance as to be ignored. Accordingly, a bandwidth of the stem is g determined just by the parasitic capacitance. Especially, since ^rof the low melting

glass 302 is generally determined to be 5.5, the stem hall radius/leads radius should be

increased in order to obtain maximum bandwidth of the stem. However, the radius of

leads 305 is commonly restricted by the thickness of the leads, and the radius of stem hall 304 is restricted by the size of the stem and the number of the leads connected to the

stem.

Accordingly, a diameter of the stem hall is restricted within the range of about 400 to 450μm in general to-can package adopting three or four leads having a diameter of 300 to 350 m. As a result, a stem bandwidth of the to-can package having the conventional metal stem structure becomes narrower.

Various methods are recently proposed for overcoming the restriction of bandwidth. The first method is to ground a stem. However a bandwidth of the stem is actually restricted in about 2.5GHz even in this method.

The second method is to making the stem electrically floated. In this case, the parasitic capacitance becomes smaller than that in the case of grounding a stem, since the grounding becomes another leads and the stem becomes one equipotential surface. Accordingly, a bandwidth is improved above 7.8GHz.

The third method is to apply signals through two coupled lines. In this method, a bandwidth may be about 10GHz, however the reflection coefficient Sll disadvantageously increases rapidly at 7GHz.

Values of S parameter calculated by the above methods are illustrated in FIG. 3d. The values represented in the graph are calculated by HFSS (High Frequency Structure Simulator). Here, a reference numeral 306 denotes a Sll characteristic curve, 307 denotes a S21 characteristic curve, and 308 denotes 3dB line.

As shown in FIG. 3d, though a stem bandwidth is more or less improved by using the above methods, the conventional methods still give no solutions for overcoming the restriction of the bandwidth according to the structure of the stem and the leads.

DISCLOSURE OF INVENTION

The present invention is designed on the consideration of the above problems. Therefore, one object of the present invention is to provide a to-can package having a broad bandwidth by replacing the conventional metal stem with a nonconductive dielectric substance such as a ceramic stem and forming a high frequency transmission line such as microstrip or coplanar wave guide (CPW) on a surface of the stem instead of the leads to thereby obtain relatively small parasitic capacitance and parasitic inductance.

Another object of the present invention is to provide a to-can package having an improved reflectance ratio according to impedance matching, since the use of transmission lines made of a thin film such as a microstrip or a coplanar wave guide (CPW) enables to produce an impedance having various characteristics.

. In order to accomplish the above object, the present invention provides a to-can package for high speed data communications, which includes an optical element, a stem for mounting the optical element, and a transmission line installed in the stem for electrical connection with the optical element. Here, the stem is made of nonconductive dielectric substance enabling process of metal film patterning. Preferably, the stem may be made of ceramic.

In addition, the transmission line is a high frequency transmission line of a microstrip, a CPW (coplanar waveguide), and a micro-coupled line, and the transmission line is preferably formed on a surface of the ceramic stem in a pattern. Furthermore, an impedance value of the high frequency transmission line is preferably designed for realizing impedance matching.

Moreover, the to-can package further includes a cap combined with the stem for covering the optical element, and a seam seal metal line protruding toward the cap for connection with the stem. Here, the seam seal metal line may radiate conductive heat of the optical element by being in contact with the optical element.

In another aspect of the present invention, a to-can package includes an optical element, a stem for mounting the optical element and made of nonconductive dielectric substance enabling a process of metal film patterning, a first transmission line of a microstrip, a CPW (coplanar waveguide), or a micro-coupled line formed on a surface of the stem in a pattern, a protrusion provided on one side of the stem and made of the same material as the stem and a second transmission line formed on the protrusion. At this time, the first transmission line is electrically connected with the second transmission line, and the second transmission line is electrically connected with the optical element.

BRIEF DESCRIPTION OF THE DRAWINGS

These and other features, aspects, and advantages of preferred embodiments of the present invention will be more fully described in the following detailed description, taken accompanying drawings. In the drawings:

FIG. la is a perspective view showing a to-can package for laser diode using a conventional metal stem;

FIG. lb is a perspective view showing a to-can package for photo diode using a conventional metal stem; FIG. 2 is an enlarged view showing a stem and a leads in a to-can package using a conventional metal stem;

FIG. 3a is a perspective view showing a stem and a leads in a to-can package using a conventional metal stem;

FIG. 3b is a diagram modeling a stem and a leads into a 2 port microwave system;

FIG. 3c is a side view showing a stem and a leads in a to-can package using a conventional metal stem;

FIG. 3d is a graph showing S parameter characteristic of a to-can package using a conventional metal stem;

FIGs. 4a and 4b are perspective views showing a to-can package for laser diode according to one preferred embodiment of the present invention;

FIGs. 4c and 4d are perspective views showing a to-can package for photo diode according to one preferred embodiment of the present invention; FIG. 5 is a graph showing S parameter characteristic of a to-can package according to one preferred embodiment of the present invention; and

FIGs. 6a to 6e are perspective views showing to-can packages according to various embodiments of the present invention.

BEST MODES FOR CARRYING OUT THE INVENTION

Hereinafter, preferred embodiments of the present invention will be described in detail with reference to the accompanying drawings.

FIGs. 4a and 4b are perspective views showing a to-can package for laser diode according to one preferred embodiment of the present invention. Referring to FIGs. 4a and 4b, the to-can package for laser diode includes a laser diode (LD) 401, a photo diode (PD) 402, a submount 403, a cap 405, a seam seal metal line 406, a heat sink 407, a ceramic stem 408, leads 409, a micro strip 410 for a transmission line, a lens 411, a microstrip 412 for leads bonding, a wire 413, a PD die bonding site 416, and a ceramic guide 417. The stem 408 adopts a ceramic in this embodiment, however, any nonconductive dielectric substance enabling a process of patterning metal film can be used for the stem.

In addition, the microstrip 410 and the microstrip 412 for leads bonding may be replaced with a CPW (coplanar waveguide) or micro-coupled line. Reference numeral 404 denotes projection of beam radiated from the laser diode

401.

As shown in FIGs. 4a and 4b, the laser diode 401 is mounted in the to-can package, and the photo diode 402 for monitor is mounted to the PD die bonding site 416.

In addition, the microstrip 410 is formed on the ceramic stem 408 in a metal film pattern.

As to the signal transmission, a high frequency electrical signal applied to the leads 409 travels to the to-can package through the microstrip 410 having a broad bandwidth, and then the signal is applied to the laser diode 401 through the wire 413 electrically comiected to the laser diode 401. The applied electrical signal is converted into an optical signal, and then radiated to an external system through the lens 411 located on the upper portion of the cap 405.

On the other hand, a light radiated to a rear facet of the laser diode chip 401 is detected by the photo diode 402 for monitoring the optical signal.

For wire-bonding, the ceramic guide 417 is protruded from the ceramic stem 408 toward the cap 405, and a pattern of the microstrip 412 for leads bonding is formed on the surface of the ceramic guide 417 so that the microstrip 410 for transmission line in the to-can package may be comiected to the wire 413 electrically connected with the laser diode.

Since the microstrips 410 may be individually designed to have particular characteristic impedance values, a reflection coefficient Sll according to impedance mismatching may be improved.

In addition, the seam seal metal line 406 is formed to protrude toward the cap

405 on the ceramic stem 408 to facilitate assembling the cap 405 and the stem 408. The heat sink 407 on which the submount 403 is mounted is positioned at the rear side of the ceramic guide 417. The heat sink 407 is connected to the seam seal metal line 406 so as to effectively radiate heat generated from the laser diode 401.

FIGs. 4c and 4d are perspective views showing a to-can package for photo diode according to one preferred embodiment of the present invention. Referring to FIGs. 4c and 4d, the to-can package for photo diode includes a cap

405, a ceramic stem 408, a seam seal metal line 406, leads 409, a microstrip 410, a lens

411, a microstrip 412 for lead bonding, a wire 413, a receiver photo diode 414, a wire bonding pad 418, and a photo diode bonding site 419.

The stem 408 adopts a ceramic in this embodiment, however, any nonconductive dielectric substance enabling metal film patterning process may be used as the step.

The receiver photo diode 414 is mounted in the photo diode boding site 419 in the to-can package for photo diode, as shown in FIGs.4c and 4d.

In signal transmission, an optical signal incident on the lens 411 is collected to the receiver photo diode 414 via the cap 405, and converted into an electrical signal. This converted electrical signal is transmitted to a transmission line of the microstrip

410 through the wire 413 and the wire bonding pad 418, and then connected to an external system through the leads 409 connected with the microstrip 412 for lead bonding. At this time, the microstrip 410 and the microstrip 412 for lead bonding are preferably formed on the surface of the ceramic stem 408 in a pattern. Since each of the microstrips 410 may be also designed to have particular characteristic impedance values in this embodiment, a reflection coefficient Sll according to impedance mismatching may be improved.

In addition, the seam seal metal line 406 protruding toward the cap 405 on the ceramic stem 408 facilitates assembling the cap 405 to the stem 408.

The present invention adopts a ceramic stem instead of a metal stem, and a high frequency signal is transmitted by a transmission line such as microstrip or CPW having a broad bandwidth rather than leads, which makes it possible to overcome restriction of bandwidth generated by the leads. FIG. 5 is a graph showing S parameter varying with frequency change in a preferred embodiment of the present invention in which characteristics of Sll and S21 are simulated by using HFSS (high frequency structure simulator). In the graph, reference numeral 507 denotes a characteristic curve of Sll, and 508 denotes that of S21. In this simulation, CPW is used as a transmission line of the to-can package, and outside is maintained in vacuum. In addition, each CPW is designed to have characteristic impedance of 50 Ω, and the bottom of the simulation field is kept to be grounded.

Referring to FIG. 5, a frequency band in which S21 parameter characteristic reaches -3dB is assumed above several tens GHz, and Sll characteristic at -lOdB value is increased up to about 20GHz. Accordingly, the bandwidth conventionally restricted by the leads may be broadened up to about 20 GHz.

FIGs. 6a to 6e illustrate various embodiments according to the present invention.

Here, a reference numeral 605 denotes a cap, 606 denotes a seam seal metal line, 608 denotes a ceramic stem, 609 denotes leads, 610 denotes a microstrip, 611 denotes a lens, and 613 denotes a wire.

In the to-can package of FIG. 6a, leads is not adopted so that influence of parasitic inductance generated from the leads may be completely removed. In the to-can packages of FIGs. 6b and 6c, the leads 609 is combined to the package so as to make it easy to solder on a PCB board.

In the to-can package of FIG. 6d, microstrip is formed in a certain pattern on a large ceramic stem 608 so that an IC chip 615 may be mounted to the microstrip 610.

In the to-can package of FIG. 6e, the stub pad 614 matched to 50 Ω is attached to the microstrip 610 to configure an impedance matching circuit. By using this impedance matching, a value of the reflection coefficient Sll is sufficiently decreased.

Heretobefore, the to-can package for high speed data communications according to the present invention is described in detail with reference to the drawings. However, it should be understood that the detailed description and specific examples, while indicating preferred embodiments of the invention, are given by way of illustration only, since various changes and modifications within the spirit and scope of the invention will become apparent to those skilled in the art from this detailed description. For example, the stem may be made of any nonconductive dielectric substance enabling process of metal film patterning as well as ceramic. In addition, the transmission line may adopt a micro-coupled line or CPW (coplanar waveguide) in addition to microstrip.

INDUSTRIAL APPUCABILTTY

To-can package for high speed data communications according to the present invention make it possible to manufacture various kind of packages depending on the pattern of transmission lines. In addition, the value of reflection coefficient Sll in accordance with impedance matching can be sufficiently decreased by having impedance of the transmission line with a characteristic impedance.

Moreover, the to-can package according to the present invention can broaden stem bandwidth above 20GHz as compared with the conventional to-can package, so it is possible to realize high speed data transmission. Furthermore, it is possible to make the to-can package more compact by elaborately designing transmission lines compactly without using a leads which is essentially used in the conventional to-can package.

Claims

What is claimed is;

1. A to-can package for high speed data communications comprising: an optical element; a stem for mounting the optical element; and a transmission line installed in the stem for electrical connection with the optical element, wherein the stem is made of nonconductive dielectric substance enabling process of metal film patterning.

2. The to-can package according to claim 1, wherein the stem is made of ceramic.

3. The to-can package according to claim 2, wherein the transmission line is a high frequency transmission line of a microstrip, a CPW (coplanar waveguide) or a micro-coupled line, and the transmission line is formed on a surface of the ceramic stem in a pattern.

4. The to-can package according to claim 3, wherein a impedance value of the high frequency transmission line is designed for realizing impedance matching.

5. The to-can package according to claim 1, further comprising: a cap combined with the stem for covering the optical element; and a seam seal metal line protruding toward the cap on the cap for connection with the stem, wherein the seam seal metal line radiates conductive heat of the optical element by being in contact with the optical element.

6. A to-can package for high speed data communications comprising: an optical element; a stem for mounting the optical element and made of nonconductive dielectric substance enabling a process of metal film patterning; a first transmission line of a microstrip, a CPW (coplanar waveguide) or a micro-coupled line formed on a surface of the stem in a pattern; a protrusion provided on one side of the stem and made of the same material as the stem; and a second transmission line formed on the protrusion, wherein the first transmission line is electrically connected with the second transmission line, and the second transmission line is electrically connected with the optical element.

7. The to-can package according to claim 6, wherein the stem is made of ceramic.

8. The to-can package according to claim 6, further comprising: a cap combined with the stem for covering the optical element; and a seam seal metal line protruding toward the cap on the cap for connection with the stem, wherein the seam seal metal line radiates conductive heat of the optical elementg in contact with the optical element.