Laser diode arrangement and method for manufacturing a laser diode arrangement

Abstract

A laser diode arrangement (1) comprises a laser diode chip (2) and a thin-film sensor element (3) for measuring a temperature, wherein the laser diode chip (2) is mounted on the sensor element (3).

Description

[0001] Description

[0002] Laser diode arrangement and method for manufacturing a laser diode arrangement

[0003] The present invention is directed to a laser diode arrangement comprising a laser diode and a sensor element for measuring a temperature .

[0004] The transmission of data in the form of light is increasingly important for optical communication systems , e . g . 5g networks . The transmission is achieved with the help of laser diodes . The reliability of transmission is strongly dependent on an accurate temperature control . In particular, a constant temperature of the laser diode is necessary to facilitate wavelength stabili zation during transmission through an optical fiber .

[0005] Higher integration density and smaller packaging si zes make it challenging to achieve constant temperatures for laser diodes . A decisive factor is an accurate measurement of temperature .

[0006] In known laser diode arrangements , a laser diode chip is mounted on a chip carrier, which in turn is mounted on a larger base carrier, which also acts as a heat sink . A thermo-electric cooler is mounted on top of a TO ( transistor outline ) package header alongside a sensor element placed between the laser diode chip and the thermo-electric cooler . The sensor element can be placed directly on the thermoelectric cooler but can also be located on the base carrier . In both cases , the sensor element cannot measure the temperature of the laser diode chip directly but only the temperature in the vicinity .

[0007] Patent application DE 10 2020 122 923 Al , the content of which is part of this application by reference , describes a sensor element for temperature measurement with a thin- film NTC thermistor .

[0008] It is an obj ect of the present invention to provide an improved laser diode arrangement .

[0009] According to one aspect , a laser diode arrangement comprises a laser diode chip and a thin- film sensor element for measuring a temperature of the laser diode chip . The laser diode chip is mounted on the sensor element .

[0010] By mounting the laser diode chip on the sensor element , in particular directly on the sensor element , the accuracy of the temperature measurement can be improved compared to an arrangement where the sensor element is located next to or even at a distance from the laser diode chip .

[0011] The sensor element can have the double function of a temperature sensor and heat dissipation for the laser diode chip . The sensor element can be mounted on a carrier such that the sensor element is located between the laser diode chip and the carrier .

[0012] As an example , the sensor element may replace a conventional chip carrier . It is also possible that the sensor element is provided in addition to a conventional chip carrier . In this case , the sensor element is positioned between the laser diode chip and the chip carrier . In both cases , a larger base carrier can be provided . The contacts of the sensor element and / or the laser diode chip may be electrically connected to the base carrier by wire bonds .

[0013] The sensor element may have the same lateral dimensions as the laser diode chip . The sensor element may have a thickness of 500 pm or less . More speci fically, the sensor element may have thickness of 100 pm or less or even 50 pm or less .

[0014] The sensor element may comprise an electrically insulating substrate , a functional layer comprising a material with a temperature-dependent electrical resistance , wherein the functional layer is arranged on the substrate and at least two electrodes , wherein the electrodes are formed on top or below the functional layer . The electrodes may be formed at the same height of the sensor element . The electrodes interdigitate with each other . In particular, the electrodes may comprise electrode fingers interdigitating with each other .

[0015] The sensor element may comprise two contact pads . The contact pads may be directly connected to the electrodes . The contact pads may point in a direction towards the laser diode chip or in a direction towards a carrier . When the contact pads point in the direction of a carrier, the sensor element is denoted as being flip-chip mounted .

[0016] In general , the thin- film sensor element may comprise any features of the thin- film sensor element disclosed in DE 10

[0017] 2020 122 923 Al . The laser diode chip may be connected by a conductive path on the sensor element to one of the contact pads . The conductive path may comprise a landing pad on which the laser diode chip is placed and a connection path connecting the landing pad to one of the contact pads . In particular, the conductive path may connect a cathode of the laser diode chip to a cathode contact pad .

[0018] The laser diode chip may also be directly electrically connected to a base carrier by a wire bond . In this case , the respective contacts of the laser diode chip and the sensor element can be kept separate .

[0019] When the sensor element is mounted on a chip carrier, which in turn is mounted on a larger base carrier, longer wire bonds are required . As an alternative , the laser diode chip may be electrically connected to a chip carrier by a wire bond and the chip carrier may be electrically connected to a base carrier by a further wire bond . In this case , the chip carrier may have a larger lateral dimension than the sensor element to allow a connection by a wire bond .

[0020] The laser diode chip may be mounted on the sensor element by a conductive paste . As an alternative , the laser diode chip may be mounted on the sensor element by a sintering material . It is also possible to mount the laser diode chip by soldering, e . g . by using AuSn solder . Also other means for mounting are possible as long as the temperature of mounting is not too high such that the laser diode chip and the sensitive area of the sensor element are not damaged . The sensor element , in turn, may be mounted on the carrier by a conductive paste , by a solder material or by a sintering material .

[0021] The sensor element may be flip-chip mounted on the carrier . In this case , contact pads of the sensor element point towards the carrier . The contact pads may be connected to metalli zations on the carrier by solder bumps or by sintering, for example . It is also possible that the laser diode chip is flip-chip mounted on the sensor element . In this case , two contacts of the laser diode chip point to the sensor element .

[0022] According to a further aspect , a method of manufacturing a laser diode arrangement comprises providing a laser diode chip and a thin- film sensor element for measuring a temperature . The laser diode chip is mounted on the sensor element . The laser diode arrangement may comprise any structural and functional characteristics of the laser diode arrangement as described in the foregoing .

[0023] In a further method step, the thin- film sensor element may be mounted on a carrier, wherein this method step can be carried out before or after mounting the laser diode chip on the thin- film sensor element .

[0024] The present disclosure comprises several aspects of an invention . Every feature described with respect to one of the aspects is also disclosed herein with respect to the other aspect , even i f the respective feature is not explicitly mentioned in the context of the speci fic aspect . Further features , refinements and expediencies become apparent from the following description of the exemplary embodiments in connection with the figures .

[0025] Figure 1A shows an embodiment of a laser diode arrangement in a schematic cross-sectional view,

[0026] Figure IB shows the laser diode arrangement of Fig . 1A in a schematic view on the top,

[0027] Figure 2A shows a thin- film sensor element in a schematic cross-sectional view,

[0028] Figure 2B shows the thin- film sensor element of Fig . 2A in a perspective exploded view,

[0029] Figure 3A shows a further embodiment of a laser diode arrangement in a schematic cross-sectional view,

[0030] Figure 3B shows the laser diode arrangement of Fig . 3A in a schematic view on the top,

[0031] Figure 4A shows a further embodiment of a laser diode arrangement in a schematic cross-sectional view,

[0032] Figure 4B shows the laser diode arrangement of Fig . 4A in a schematic view on the top,

[0033] Figure 5 shows a further embodiment of a laser diode arrangement in a schematic cross-sectional view,

[0034] Figure 6 shows a further embodiment of a laser diode arrangement in a schematic cross-sectional view . In the figures , elements of the same structure and / or functionality may be referenced by the same reference numerals . It is to be understood that the embodiments shown in the figures are illustrative representations and are not necessarily drawn to scale .

[0035] Figure 1A shows a laser diode arrangement 1 comprising a laser diode chip 2 in a schematic cross-sectional view . Figure IB shows the laser diode arrangement 1 on a view on the top .

[0036] The type of the laser diode chip 2 can depend on the speci fic application . As an example , it may be a Vertical Cavity Surface Emitting Laser (VCSEL ) , which is mostly used for short-distance multi-mode applications , a Fabry Perot ( FB ) laser, which is suitable for applications of short to medium reach below 10 Gbps transmission or a Distributed Feedback ( DFB ) Laser and Electro-Absorption Modulation (EM) Laser which are ideal for high-speed data rate on medium to long reach e . g . , 50 Gbps and above applications .

[0037] The laser diode chip 2 is mounted on a sensor element 3 for measuring a temperature of the laser diode chip 2 . The sensor element 3 is a thin- film NTC thermistor element ( TF-NTC ) . A general layout of a thin- film sensor element 3 is shown in Figs . 2A and 2B ( see detailed description further below) .

[0038] The laser diode chip 2 is in direct contact with the sensor element 3 , enabling an accurate detection of temperature changes with a short response time . In addition to that , the sensor element 3 acts also as a carrier and a heat sink for the laser diode chip 2 . The sensor element 3 is mounted on top of a larger base carrier 4 . The connections from the laser diode chip 2 and the sensor element 3 to the base carrier 4 are provided by wire bonds 5a, 5b, 5c . As an example , the wire bonds 5a, 5b, 5c are gold wire bonds .

[0039] The first contact pad 6a is connected by a first wire bond 5a to a first metalli zation 27a on the base carrier 4 . The second contact pad 6b is connected by a second wire bond 5b to a second metalli zation 27b on the base carrier 4 . The first contact pad 6a may be the cathode and the second contact pad 6b may be the anode of the sensor element 3 . An upper contact 32 of the laser diode chip 2 is connected by a third wire bond 5c to a third metalli zation 27c on the base carrier 4 . The upper contact may be the anode of the laser diode chip 2 .

[0040] The cathodes of the thin- film sensor element 3 and the laser diode chip 2 are shared, thereby reducing the need for an additional contact pad in the package . The shared cathode , i . e . , first contact pad 6a to which lower contact 31 of laser diode chip 2 is connected, is wire-bonded to the first metalli zation 27a on the base carrier 4 . However, the anodes of the sensor element 3 and the laser diode chip 2 are kept separate . Thereby, di f ferent electric current and voltage requirements of the laser diode chip 2 and the sensor element 3 can be complied with .

[0041] The sensor element 3 may replace a conventional carrier and heat sink . The sensor element 3 may have the same dimensions as a conventional carrier in a laser diode arrangement . The sensor element 3 may have similar dimensions as the laser diode chip 2 , with the lateral dimension being larger due to contact pads 6a, 6b at an upper side 22 of the sensor element 3.

[0042] As an example, the length and width of the contact pads 6a, 6b are in the range of 400 x 1000 pm2down to 20 x 50 pm2, whereas the thickness is between 1 pm and 0.01 pm. More specifically, length and width of the contact pads 6a, 6b may be in the range of 250 x 700 pm2down to 50 x 150 pm2, whereas the thickness may be 0.5 pm or less. In an embodiment length, width and thickness are 125 pm, 500 pm and 0.25 pm. The contact pads 6a, 6b may comprise a first layer of Ti and a second layer of Au on top. The first layer may have a thickness of 0.05 pm and the second layer may have a thickness of 0.2 pm. The thickness of each contact pad 6a, 6b is the portion of the contact pad 6a, 6b which protrudes out of the through-hole 23 of the protective layer 21.

[0043] A connection between the laser diode chip 2 and the sensor element 3 establishes an electrical and thermal contact. The sensor element 3 has a centered temperature sensitive area on which the laser diode chip 2 is placed.

[0044] The cathode of the laser diode chip 2 and the cathode (first contact pad 6a) of the underlying sensor element 3 are electrically connected by a conductive path 7. The material forming the conductive path 7 is deposited on top of a protective layer 21 of the sensor element 3. The conductive path 7 comprises one or more electrically conductive layers.

[0045] Materials such as Au, Ag, Pt, Cu, Ni, Cr, Ti, Ta, W, Al, Pd or other metals or compositions of these can be used for the conductive path 7. The conductive path 7 may comprise a first layer of Ti with 0.05 pm and a second layer of Au with 0.2 pm on top . The thickness of the conductive path 7 may be between 1 pm down to 0 . 01 pm and preferentially, 0 . 5 pm or less , for example . As a speci fic example , the conductive path 7 may have a thickness of 0 . 25 pm, for example .

[0046] The conductive path 7 comprises two sections . A first section 8 acts as a landing pad for the laser diode chip 2 . The first section 8 may have dimensions of 260 pm x 200 pm, for example . The lateral dimensions of the first section 8 and the laser diode chip 2 may be the same . The second section 9 is a connecting path connecting the first section 8 with the first contact pad 6a . The connecting path may have a width and length of 50 pm x 50 pm . One dimension may be substantially smaller than the other dimension .

[0047] The maximum width of the conductive path 7 is the same as the si ze of the sensor element 3 , whereas the maximum length is less than the distance between the two contact pads 6a, 6b so that the conductive path 7 is separated from the second contact pad 6b to prevent a short circuit . The free space between the conductive path 7 and the second contact pad 6b may be of at least 5 pm in length and extends along the entire width of the second contact pad 6b .

[0048] The minimum width of the conductive path 7 is 5 pm and the minimum length is the distance between the contact pads 6a, 6b and the closest edge of the sensitive area of the sensor element 3 . Other dimensions and geometries of the conductive path 7 between the largest and smallest si ze as described are also possible .

[0049] The laser diode chip 2 is connected to the conductive path 7 by a conductive material 24 , which may be a conductive paste . It is preferable to keep a spacing of at least l / 3rd of the height of the laser diode chip 2 between the first section 8 ( landing pad) and either side of the contact pads 6a, 6b to prevent the spillover of the conductive material 24 while mounting the laser diode chip 2 . For example , for a laser diode chip 2 having a height of 100 pm, a spacing of 100 pm is kept between the first section 8 ( landing pad) and the two contact pads 6a, 6b of the sensor element 3 on either side . The laser diode chip 2 may also have a distance of about 100 pm from the lateral edges of the sensor element 3 in the width direction .

[0050] The sensor element 3 provides the function of a conventional NTC-element which usually is mounted at a lateral distance from the laser diode chip 2 , e . g . on the base carrier 4 or a thermo-electric cooler (not depicted) . In such a conventional arrangement , the sensor element 3 cannot measure the temperature of the laser diode chip 2 directly but measures only the temperature changes in its vicinity . Due to the direct measurement enabled with the shown arrangement , the temperature control is improved, and a constant temperature can be maintained more accurately .

[0051] The laser diode arrangement 1 may be packaged using di f ferent techniques . The most common packages are the TO ( Transistor Outline ) package and 14-pin butterfly . For a TO package , the number of pins indicates the components inside the package . The laser diode arrangement 1 may comprise a thermo-electric cooler . The thermo-electric cooler can be placed on top of the TO package and the base carrier and other mountings are done on top of the thermo-electric cooler . The shown laser diode arrangement 1 may be a 5-pin arrangement , wherein two pins are for the anodes of the laser diode chip 2 and the sensor element 3 , one pin is for the combined cathode of the laser diode chip 2 and the sensor element 3 and two pins are for the thermo-electric cooler . Without a thermos-electric cooler, the arrangement 1 is a 3- pin arrangement .

[0052] Figure 2A shows a thin- film NTC sensor element 3 which can be used in the laser diode arrangement 1 of Figs . 1A and IB . Figure 2B shows the thin- film NTC sensor element 3 in an exploded view .

[0053] The sensor element 3 comprises an insulating substrate 10 . The substrate 10 comprises a main substrate body 11 having a good thermal conductivity and, thereby, acting as a heat sink for the laser diode chip 2 . The main substrate body 11 comprises AIN, S13N4 , A12O3 or other ceramics , for example .

[0054] The main substrate body 11 has an upper side 12 and a lower side 13 . On the upper side 12 an insulating layer 14 is provided, for example comprising SiO2 . The insulating layer 14 is a protective layer for the main substrate body 11 .

[0055] The sensor element 3 comprises two electrodes 15a, 15b . The electrodes 15a, 15b are arranged directly on the insulating layer 14 of the substrate 10 . The electrodes 15a, 15b are formed from thin metal films .

[0056] The electrodes 15a, 15b are designed as interdigital thin- film electrodes . In particular, the electrodes 15a, 15b each have an extended end section 16 and a section with electrode fingers 17 . The section of the electrode fingers 17 is formed in a center area of the substrate 10 . The electrode fingers 17 extend from the flat end section 16 . The two electrodes 15a, 15b interlock in the area of the electrode fingers 17 in the center area of the substrate 10 and form an interdigital structure there . The electrodes 15a, 15b are located at the same height in the sensor element 3 . The sensor element 3 may comprise only electrodes 15a, 15b at this height but no further electrode layers .

[0057] The sensor element 3 comprises a functional layer 18 with a top side 19 and a bottom side 20 . The functional layer 18 is an NTC thin film . The functional layer 18 only partially covers the insulating layer 14 on the upper side 12 of the main substrate body 11 . The functional layer 18 is at least partially applied on the electrodes 15a, 15b . The electrodes 15a, 15b are formed between the substrate 10 and the functional layer 18 , in particular the bottom side 20 of the functional layer 18 . The functional layer 18 is arranged directly on the electrode fingers 17 .

[0058] Each of the contact pads 6a, 6b of the sensor element 3 is connected to one of the electrodes 15a, 15b . The contact pads 6a, 6b are arranged on the respective end section 16 of the electrodes 15a, 15b .

[0059] The sensor element 3 comprises a protective layer 21 . The protective layer 21 completely covers an upper side 22 of the sensor element 3 with the exception of through-holes 23 for the contact pads 6a, 6b . The contact pads 6a, 6b protrude beyond an upper side 22 of the protective layer 21 for electrical contacting of the sensor element 3 . As an example , the total length 1 and width b of the thin- film sensor element 3 may be in the range of 1000 x 1000 pm2to 50 x 50 pm2. The thickness d may be 500 pm or less , for example . In particular, the thickness may be 150 pm or less . The thickness d may be measured without a part of the contact pads 6a, 6b protruding out of a protective layer of the sensor element 3 . More speci fically, the sensor element 3 may have a length and width of 700 x 700 pm2to 150 x 150 pm2with a thickness d of 300 pm or less . One example is a length 1 of 650 pm, a width b of 550 pm and a thickness d of 280 pm .

[0060] The sensor element 3 may be manufactured by the following method . The main substrate body 11 is formed . A material of the main substrate body 11 may comprises Si , SiC or glass . Alternatively, the material may comprise AIN or A12O3 . The main substrate body 11 has an upper side 12 and a lower side 13 . The electrically insulating layer 14 is formed on the upper side 12 of the main substrate body 11 .

[0061] Two electrodes 15a, 15b are deposited on the substrate 10 . The deposition can be carried out by a PVD ( "physical vapour deposition" ) process , a CVD ( " chemical vapour deposition" ) process or galvanically . The electrodes 15a, 15b can be structured in a further process step . The electrodes 15a, 15b interlock in the form of interdigital structures . The electrodes 15a, 15b can be formed in such a way that they are spaced from an edge area of the substrate 10 .

[0062] The functional layer 18 is applied, e . g . by sputtering a functional material , to a partial area of the electrodes 15a, 15b . In particular, the functional layer 18 is formed in such a way that it is spaced from the edge area of the insulating substrate 10 and is formed on the area of the finger interdigital structures of the electrodes 15a, 15b . The functional layer 18 can be deposited as a full-surface thin film and structured in a further process step, e . g . by means of lithography .

[0063] The functional material may comprise an NTC ceramic based on an oxidic material in the perovskite or spinel structure type . Alternatively, the functional material may be based on a carbide or nitride material or on vanadium oxide or SiC .

[0064] After deposition, the functional layer 18 is not yet crystalli zed . The functional layer 18 is then sintered to obtain the NTC properties . The sintering process may be carried out at temperatures of up to 1000 ° C .

[0065] It is also possible that the functional layer 18 is first formed on a partial area of the substrate 10 and the electrodes 15a, 15b are then formed on an upper side of the functional layer 18 .

[0066] The protective layer 21 is applied to the top side 19 of the functional layer 18 . The protective layer 21 completely covers the upper side 22 except for two through-holes 23 . The partial areas are arranged over the extended end sections 16 of the electrodes 15a, 15b to which the contact pads 6a, 6b can be deposited in a subsequent process step . For structuring, the protective layer 21 can be either applied over the entire surface and the free partial areas produced by a subsequent process such as lithography or laser structuring or directly structured by using a mask during the deposition process . The contact pads 6a, 6b are formed through the protective layer 21 for electrical contacting of the sensor element 3 . Each of the contact pads 6a, 6b contacts an extended end section 16 . The contact pads 6a, 6b can protrude beyond the functional layer 18 .

[0067] The contact pads 6a, 6b may comprise Cu, Au, Ni , Cr, Ag, Ti , W, Pd or Pt as a material . As a speci fic example , the contact pads 6a, 6b are made of Cu . Preferably, the contact pads 6a, 6b have a thickness of > 5 pm . As an alternative to the contact pads 6a, 6b, bumps or thin electrodes can be provided .

[0068] The sensor element 3 may be manufactured from a larger component which is then separated into single , discrete sensor elements 3 . A separation in a length and width direction may be carried out by plasma etching or sawing and notching . A grinding process may be carried out from the lower side 13 to remove material of the insulating substrate 10 up to a defined final component thickness .

[0069] Figures 3A and 3B show a further embodiment of a laser diode arrangement 1 in a cross-sectional view and a view on the top . As in Figs . 1A and IB, a laser diode chip 2 is mounted directly on a thin- film sensor element 3 . The thin- film sensor element 3 can be in accordance with the sensor element 3 of Figs . 2A and 2B .

[0070] The di f ference to Figs . 1A and IB is that a conventional chip carrier 26 is provided, wherein the sensor element 3 is arranged between the laser diode chip 2 and the chip carrier 26 . Accordingly, both the sensor element 3 and the chip carrier 26 act as carriers for the laser diode chip 2 . The sensor element 3 may be mounted on the chip carrier 26 by a conductive paste . As examples , Ag screen printing or other means such as AuSn solder can be used .

[0071] The sensor element 3 may have a smaller thickness d than the sensor element 3 of Figs . 1A and IB, as the function of a heat sink is also provided by the chip carrier 26 . As an example , the thickness d of the sensor element 3 may be 50 pm or less .

[0072] The length and width may be the same as described for the sensor element 3 in the foregoing example . As an example , the sensor element 3 may have a length and width of 700 x 700 pm2to 150 x 150 pm2and a thickness d of 50 pm or less . A speci fic example is a length 1 of 650 pm ± 10 pm, a width b of 550 pm ± 10 pm and a thickness d of 50 pm ± 10 pm .

[0073] The thickness of the chip carrier 26 may be greater than the thickness of the sensor element 3 . The thickness of the chip carrier 26 may be at least three times the thickness of the sensor element 3 . As an example , the thickness of the chip carrier 26 may be 280 pm and the thickness of the sensor element 3 may be 50 pm .

[0074] As in the embodiment of Figs . 2A and 2B, the cathode of the laser diode chip 2 and the cathode ( first contact pad 6a ) of the underlying sensor element 3 are electrically connected by a conductive path 7 comprising a first section 8 and a second section 9 .

[0075] The first contact pad 6a is connected by a first wire bond 5a to a first metalli zation 27a on the base carrier 4 . The second contact 6b is connected by a second wire bond 5b to a second metalli zation 27b on the base carrier 4 . The anode of the laser diode chip 2 is connected by a third wire bond 5c to a third metalli zation 27c on the base carrier 4 . Due to the increased total thickness of sensor element 3 and chip carrier 26 , longer wire bonds 5b, 5c are required .

[0076] Figures 4A and 4B show a further embodiment of a laser diode arrangement 1 in a cross-sectional view and a view on the top . The arrangement 1 di f fers from the arrangement 1 of Figs . 3A and 3B only in the electrical connection of the anode of the laser diode chip 2 to the third metalli zation 27c on the base carrier 4 .

[0077] In this embodiment , the anode of the laser diode chip 2 is not directly connected to the third metalli zation 27c on the base carrier 4 by a wire bond but connected by a wire bond 5c to a metalli zation 28 on the chip carrier 26 . The metalli zation 28 is connected by a wire bond 5d to the third metalli zation 27c on the base carrier 4 . In this case , two shorter wire bods 5c, 5d can be used .

[0078] The chip carrier 26 is larger in a lateral dimension than the sensor element 3 such that space is provided for the metalli zation 28 . The length and width of the sensor element 3 can be in the range of 1000 x 800 pm2down to 50 x 30 pm2'forexample . The thickness can be 150 pm or less . As an example , the length and width of the sensor element 3 is 700 x 500 down to 150 x 100 pm2with a thickness of 50 pm or less . As a speci fic example , the sensor element 3 has dimensions of 650 pm ± 10 pm, a width b of 300 pm ± 10 pm and a thickness d of 50 pm ± 10 pm . As an example, the length and width of the contact pads 6a, 6b are in the range of 400 x 800 pm2down to 20 x 50 pm2, whereas the thickness is between 1 pm and 0.01 pm. More specifically, length and width of the contact pads 6a, 6b may be in the range of 250 x 500 pm2down to 50 x 150 pm2or 50 x 100 pm2, whereas the thickness may be 0.5 pm or less. As a specific example, a sensor element 3 has dimensions 1, b, d of 125 pm, 300 pm and 0.25 pm.

[0079] The chip carrier 26 may have the same length as the sensor element 3 and a larger width than the sensor element 3. As an example, the chip carrier 26 has a width of 550 pm, while the sensor element 3 has a width of 300 pm.

[0080] A sufficient distance is required between the contact paths of the sensor element 3 and the metallization 28 on the chip carrier 26 to prevent short-circuiting by a spillover of the conductive paste while mounting. As an example, a lateral distance in the range of 700 pm down to 10 pm is sufficient. As a specific example, the distance is 125 pm.

[0081] According to a further embodiment, also the cathode contacts for the sensor element 3 and the laser diode chip 2 are separate. In this case, the cathode of the laser diode chip 2 can be directly connected by a wire bond to a metallization on the base carrier 4 as is shown for the anode in Figs. 3A and 3B. In this case, the laser diode arrangement 1 can be 6- pin arrangement. It is also possible that the cathode of the laser diode chip 2 is connected to a metallization on the chip carrier 26 by a wire bond and the metallization is connected to a metallization on the base carrier 4 by a further wire bond as shown for the anode in Figs. 4A and 4B. Figure 5 shows a further embodiment of a laser diode arrangement 1 in a cross-sectional view . In this embodiment , the sensor element 3 is flip-chip mounted .

[0082] Also here , the laser diode chip 2 is directly mounted on the thin- film sensor element 3 . The sensor element 3 can be mounted on a chip carrier 26 , which in turn can be mounted on a larger base carrier 4 . It is also possible that the sensor element 3 is directly mounted on a larger base carrier 4 . The sensor element 3 , chip carrier 26 and base carrier 4 can be as in the foregoing embodiments .

[0083] In the shown embodiment , the contact pads 6a, 6b are implemented for a connection by solder bumps 29 for a soldering process . The contact pads 6a, 6b are soldered to metalli zations 28a, 28b on the chip carrier 26 .

[0084] The design and material of the contact pads 6a, 6b is configured for a soldering process . The minimum si ze of the contact pads 6a, 6b is the si ze of one solder bump 29 which typically has a diameter of 400 down to 1 pm . As an example , a solder bump 29 has a diameter of 150 pm or smaller . The maximum si ze for the contact pads 6a, 6b is the same as described in the foregoing embodiments .

[0085] It is also possible to arrange bumps in the form of an array on the contact pads 6a, 6b . In case of more than one solder bump 29 , a pitch of 150 pm or smaller has to be kept between each bump 29 in the array .

[0086] The height of the solder bumps 29 can be in the range of 250 pm down to 1 pm, preferentially, 50 pm or smaller . Materials such as Cu, Au, Ni , Sn, Co , SAC ( SnAgCu) or other bumping materials or compositions of these can be used . To ensure a good adhesion of the solder bumps , an under-bump- metalli zation (UBM) can also be used . Materials such as Ni , Cr, Ti , Ta, Pt , Pd, W, Cu, Al , Au or other metals or compositions of these are used for the UBM . The dimensions of the UBM could cover the entire contact pad 6a, 6b of the sensor element 3 or be at least the dimensions of the base of the solder bumps 29 .

[0087] Optionally, an epoxy based or Si02 based or other polymer based underfill is deposited throughout the contact pads 6a, 6b and then cured for better reliability of the solder bumps .

[0088] To ensure contactability of the laser diode chip 2 , a back side metalli zation 30 is applied to the sensor element 3 . The material of the back side metalli zation 30 can be the same as for the contact pads 6a, 6b described above in the foregoing embodiments .

[0089] The insulating substrate 10 of the sensor element 3 is located between the laser diode chip 2 and the functional layer 18 of the sensor element 3 . The further components of the sensor element 3 like protective layer 21 and electrodes 15a, 15b are not depicted here . The sensor element 3 can be as shown in Figs . 2A and 2B .

[0090] The sensor element 3 can have the same geometrical dimensions as in the foregoing embodiments .

[0091] The laser diode chip 2 comprises a first ( lower ) contact 31 and a second (upper ) contact 32 . The first contact 31 is directly connected to the back-side metalli zation 30 . The back-side metalli zation 30 can be connected by a wire-bond to a metallization on a base carrier. The upper contact 32 of the laser diode chip 2 can be connected to a further metallization on the base carrier.

[0092] Also here, one of the contacts of the laser diode chip 2 and the sensor element 3 can be shared and the other contact can be separate. As an example, the back-side metallization 30 can be connected by a wire bond to the second metallization 28b on the chip carrier 26. The second metallization can be connected by a wire bond to the base carrier. It is also possible that the back-side metallization 30 is connected by a wire bond to a metallization on the base carrier, wherein the sensor element 3 is connected to the same metallization. The back-side metallization 30 may be connected to the cathode of the laser diode chip 2.

[0093] It is also possible to keep both the positive and negative contacts separate. Accordingly, either a 5-pin or 6-pin layout comprising a thermo-electric cooler or a 3-pin or 4- pin layout without a thermos-electric cooler is possible.

[0094] In an alternative embodiment, the laser diode chip 2 can be flip-chip mounted on the sensor element 3 instead of screen printing. In that case, two lower contacts are provided on the laser diode chip 2. The back-side metallization 30 may then be replaced by two metallizations 30 which are not electrically connected to each other. As an example, the metallizations may be separated by 50 - 250 pm. One of the contacts of the laser diode chip 2 is connected to one of the metallizations and the other one of the contacts is connected to the other metallization. Each of the metallizations can then be connected by a wire bond to the base carrier. Figure 6 shows a further embodiment of a laser diode arrangement 1 in a cross-sectional view . Also here , the sensor element 3 is flip-chip mounted .

[0095] The di f ference to the foregoing embodiment is that the sensor element 3 is fixed by a sintering process to metalli zations 28a, 28b on the chip carrier 26 . The contact pads 6a, 6b of the sensor element 3 are designed for a sintering process , in particular for a silver (pressure ) sintering process . The material of the contact pads 6a, 6b is Ag- or Au-based .

[0096] The thickness of the contact pads 6a, 6b has to suf ficiently exceed the thickness of the functional layer 18 . The thickness of the contact pads 6a, 6b is 100 nm or thicker, for example .

[0097] To ensure a contactability of the laser diode chip 2 , a backside metalli zation 30 is applied to the sensor element 3 . The material of this back-side metalli zation 30 can be the same as for the contact pads 6a, 6b so that the laser diode chip 2 can be mounted by silver (pressure ) sintering as well .

[0098] Alternatively, the back-side metalli zation 30 is the same as for the contact pads 6a, 6b described above for conventional mounting of the laser diode chip 2 .

[0099] The connection to a base carrier can be as described for the embodiment of Figure 5 . Reference numerals

[0100] 1 laser diode arrangement

[0101] 2 laser diode chip

[0102] 3 sensor element

[0103] 4 base carrier

[0104] 5a wire bond

[0105] 5b wire bond

[0106] 5c wire bond

[0107] 5d wire bond

[0108] 6a first contact pad

[0109] 6b second contact pad

[0110] 7 conductive path

[0111] 8 first section ( landing pad)

[0112] 9 second section ( connecting path)

[0113] 10 insulating substrate

[0114] 11 main substrate body

[0115] 12 upper side

[0116] 13 lower side

[0117] 14 insulating layer

[0118] 15a first electrode

[0119] 15b second electrode

[0120] 16 end section

[0121] 17 electrode finger

[0122] 18 functional layer

[0123] 19 top side

[0124] 20 bottom side

[0125] 21 protective layer

[0126] 22 upper side

[0127] 23 through-hole

[0128] 24 conductive material

[0129] 25 spillover

[0130] 26 chip carrier 27a first metallization (on base carrier)

[0131] 27b second metallization (on base carrier)

[0132] 27c third metallization (on base carrier)

[0133] 28 metallization (on chip carrier) 28a first metallization (on chip carrier)

[0134] 28b second metallization (on chip carrier)

[0135] 29 solder bump

[0136] 30 back-side metallization

[0137] 31 first contact (of laser diode chip) 32 second contact (of laser diode chip)

[0138] 1 length b width d thickness

Claims

Claims1. A laser diode arrangement (1) , comprising a laser diode chip (2) and a thin-film sensor element (3) for measuring a temperature, wherein the laser diode chip (2) is mounted on the sensor element (3) .

2. The laser diode arrangement (1) of claim 1, wherein the sensor element (3) comprises a functional layer (18) comprising a material with a temperature-dependent electrical resistance, an insulating substrate (10) and two electrodes (15a, 15b) , wherein the electrodes (15a, 15b) are formed on top or below the functional layer (18) , and wherein the electrodes (15a, 15b) are formed on the same height and interdigitate with each other.

3. The laser diode arrangement (1) of any of the preceding claims, wherein a thickness of the sensor element (3) is 500 pm or less.

4. The laser diode arrangement (1) of any of the preceding claims, wherein the sensor element (3) is mounted on a carrier (4, 26) such that the sensor element (3) is located between the laser diode chip (2) and the carrier (4, 26) .

5. The laser diode arrangement (1) of claim 4, wherein the sensor element (3) and / or the laser diode chip(2) is electrically connected to the carrier (4, 26) by wire bonds (5a, 5b, 5c, 5d) .

6. The laser diode arrangement (1) of any of the preceding claims, wherein the sensor element (3) comprises two contactpads (6a, 6b) for electrical connection of the sensor element (3) .

7. The laser diode arrangement (1) of claim 6, wherein the laser diode chip (2) is connected by a conductive path (7) on the sensor element (3) to one of the contact pads (6a, 6b) .

8. The laser diode arrangement (1) of any of claims 6 or 7, wherein the contact pads (6a, 6b) are electrically connected to a base carrier (4) by wire bonds (5a, 5b) .

9. The laser diode arrangement (1) of any of the preceding claims, wherein the laser diode chip (2) is directly electrically connected to a base carrier (4) by a wire bond (5d) .

10. The laser diode arrangement (1) of any of the preceding claims, comprising a chip carrier (26) on which the sensor element (3) is mounted and a base carrier (4) on which the chip carrier (26) is mounted, wherein the laser diode chip (2) is electrically connected to the chip carrier (26) by a wire bond (5c) and the chip carrier (26) is electrically connected to the base carrier (4) by a further wire bond (5d) .

11. The laser diode arrangement (1) of any of the preceding claims, wherein the laser diode chip (2) is mounted on the sensor element (3) by a conductive paste, by a sintering material or by solder material.

12. The laser diode arrangement (1) of any of the preceding claims, wherein the sensor element (3) is mounted on acarrier (4, 26) by a conductive paste, by a solder material or by a sintering material.

13. The laser diode arrangement (1) of any of the preceding claims, wherein the sensor element (3) is flip-chip mounted.

14. The laser diode arrangement (1) of claim 13, wherein the sensor element (3) comprises an electrically insulating substrate (10) on which a functional layer (18) comprising a material with a temperature-dependent electrical resistance is arranged, wherein the insulating substrate (10) is located between the laser diode chip (2) and the functional layer (18) , and at least two contact pads (6a, 6b) pointing in the direction of a carrier (4, 26) on which the sensor element (3) is mounted.

15. The laser diode arrangement (1) of any of the preceding claims, wherein one contact of the sensor element (3) and the laser diode chip (2) is shared and another contact is separate .

16. A method of manufacturing the laser diode arrangement (1) of any of the preceding claims, comprising the steps ofA) providing the laser diode chip (2) and the thin-film sensor element (3) andB) mounting the laser diode chip (2) on the thin-film sensor element (3) .

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