DE102017111802A1 - Radiation detector and method of making a radiation detector - Google Patents

Abstract

A radiation detector (1) for detecting a signal radiation (8) having a semiconductor component (2) and a housing (3) in which the semiconductor component is arranged is provided, wherein a gap (33) between the semiconductor component and the housing is provided with a Blocking layer (5) is filled.
Furthermore, a method for producing a radiation detector is specified.

Description

The present application relates to a radiation detector and to a method for producing a radiation detector.

For many optical sensor applications, a high signal-to-noise ratio is essential. For this purpose, the radiation detector provided for detection should generate a signal only as possible in response to the signal radiation to be detected. A significant contribution to the noise level is often provided by ambient light or so-called "optical noise".

An object is to provide a radiation detector, which is characterized by a high signal-to-noise ratio and at the same time is easy to produce. Furthermore, a method is to be specified with which a simple and reliable production of a radiation detector can be achieved.

These objects are achieved inter alia by a radiation detector or a method according to the independent patent claims. Further embodiments and expediencies are the subject of the dependent claims.

A radiation detector for detecting a signal radiation is specified. The signal radiation is, for example, in the visible spectral range. For example, the signal radiation is a partial region of the visible spectral range, for example with a full half-width of at most 100 nm or 150 nm, or the entire visible spectral range. Alternatively, the signal radiation may also be in the ultraviolet or infrared spectral range.

The radiation detector is, for example, a surface mounted device (smd).

In accordance with at least one embodiment of the radiation detector, the radiation detector has a semiconductor component. The semiconductor component is, for example, a photodiode or a phototransistor. In particular, the semiconductor component can be designed as an unhoused semiconductor component. The semiconductor component itself therefore has no housing. By way of example, the semiconductor component is a semiconductor chip which has emerged, for example, by singulation from a wafer composite.

The semiconductor component, in particular a photosensitive region of the semiconductor component, is based for example on a semiconductor material, for example silicon. Alternatively, it is also possible to use another semiconductor material, for example a III-V compound semiconductor material or a II-VI compound semiconductor material.

In accordance with at least one embodiment of the radiation detector, the radiation detector has a housing. The housing is for example a prefabricated housing. Such a housing is also referred to as a pre-mold housing. For example, the housing has at least two external contacts for the external electrical contacting of the radiation detector. The external contacts are formed, for example, by means of a lead frame, which is formed by a housing body of the housing. The housing body itself is expediently designed to be electrically insulated.

The semiconductor device is disposed in the housing, such as in a cavity of the housing.

In accordance with at least one embodiment of the radiation detector, a gap between the semiconductor component and the housing is filled with a blocking layer. In the lateral direction, the semiconductor component is surrounded at least in places by the blocking layer. For example, the blocking layer directly adjoins the semiconductor component in places, in particular on a side surface of the semiconductor component.

A lateral direction is in doubt a direction parallel to a mounting surface of the radiation detector.

The blocking layer is in particular completely impermeable to at least part of the electromagnetic spectrum. In particular, the blocking layer can be spectrally broadband radiopaque, at least in a range between 400 nm inclusive and including 1000 nm.

In at least one embodiment of the radiation detector, the radiation detector is provided for detecting a signal radiation and has a semiconductor component and a housing, wherein the semiconductor component is arranged in the housing and a gap between the semiconductor component and the housing is filled with a blocking layer.

By means of the blocking layer, the surface through which radiation can enter the semiconductor component and contribute to a signal can be essentially limited to a radiation entrance surface of the semiconductor component. The radiation entrance surface extends, for example, parallel to the mounting surface of the radiation detector. Radiation coupling through an oblique or perpendicular to the radiation entrance surface extending Side surface of the semiconductor device can be suppressed or at least reduced.

In accordance with at least one embodiment of the radiation detector, the blocking layer completely covers all side surfaces of the semiconductor component. At least for spectral components for which the blocking layer is impermeable, the radiation coupling can thus be reduced completely to the radiation entrance surface of the semiconductor component. It has been found that disproportionately much interference is coupled in conventional radiation detectors via the side surfaces of the semiconductor component. Therefore, the stronger the radiation coupling through the side surfaces of the semiconductor device is suppressed, the better the signal-to-noise ratio of the radiation detector can be.

In accordance with at least one embodiment of the radiation detector, the blocking layer is impermeable at least for radiation of between 700 nm and 1000 nm inclusive. It has been found that ambient radiation in this spectral range provides a significant contribution to the noise of the radiation detector, in particular when using a semiconductor component based on silicon.

In accordance with at least one embodiment of the radiation detector, the blocking layer is impermeable to the signal radiation. Contrary to the usual endeavor, therefore, a reduction of the signal due to the reduced radiation coupling in of the signal radiation via the side surface of the semiconductor component is accepted. It has been found that proportions of the detector signal generated by the signal radiation drop less in percentage than signal components which are caused by scattered radiation. This increases the overall signal-to-noise ratio of the radiation detector.

In accordance with at least one embodiment of the radiation detector, the blocking layer is impermeable to at least a part of radiation in the ultraviolet, for radiation in the visible and for a part of radiation in the infrared spectral range. The blocking layer is thus spectrally broadband radiopaque. For example, the blocking layer is impermeable to radiation having wavelengths between 400 nm inclusive and 1100 nm inclusive.

According to at least one embodiment of the radiation detector, the blocking layer contains black pigments embedded in a matrix material, such as soot. For example, additives, such as those sold under the name "Printex 300" by Degussa additives or equivalent products from other manufacturers are suitable. As a matrix material, for example, a polymer material, such as a silicone or an epoxy is suitable.

According to at least one embodiment of the radiation detector, the blocking layer contains carbon black. Carbon black is characterized by a spectrally broadband and efficient radiation absorption, so that a blocking layer can be produced easily and reliably.

In accordance with at least one embodiment of the radiation detector, a radiation entrance surface of the semiconductor component is at least locally free of the blocking layer. For example, the semiconductor device or at least its photosensitive region is at least 90% or at least 95% of its footprint free of blocking layer material in plan view of the radiation detector. The blocking layer thus does not hinder or at least not substantially hinder radiation coupling in through the radiation entrance surface of the semiconductor component.

In accordance with at least one embodiment of the radiation detector, a filter is arranged on the radiation entrance surface of the semiconductor component. The filter is intended in particular for adapting the spectral sensitivity of the semiconductor component to a spectral sensitivity distribution predetermined for the radiation detector. For example, the filter is a dielectric filter having a plurality of dielectric layers, such as a Bragg reflector. By way of the layer thicknesses and the refractive indices of the individual dielectric layers, the spectral transmission can be adapted within wide limits to a predetermined spectral transmission. The filter can be attached to the semiconductor component as a prefabricated element, for example by means of a connection layer, or integrated into the semiconductor component, for example in the form of a coating of the semiconductor component. The values given below for the transmission of the filter relate in each case to radiation incident perpendicular to the radiation entrance surface.

In particular, the blocking layer adjoins a side surface of the filter. The blocking layer thus also prevents lateral coupling into the filter.

In accordance with at least one embodiment of the radiation detector, the filter is a bandpass filter which transmits radiation in the visible spectral range. For example, a transmission of the filter between 450 nm and 600 nm including inclusive at least 50% of the maximum transmission of the filter. Radiation with a wavelength above 650 nm up to to a cut-off wavelength of the radiation detector, for example at a wavelength of about 1100 for a silicon-based photosensitive area, is blocked or at least attenuated by means of the filter.

In accordance with at least one embodiment of the radiation detector, a gap between the semiconductor component and the housing and a viscosity of the material of the blocking layer in the liquid state are matched to one another such that capillary forces promote filling of the gap along at least three side surfaces of the semiconductor component. The production of the radiation detector in which all four side surfaces of the semiconductor device are covered in places, preferably completely, with the blocking layer is thus simplified.

In accordance with at least one embodiment of the radiation detector, a lateral distance between the semiconductor component and the housing at three side surfaces of the semiconductor component is between 50 μm and 200 μm inclusive. It has been shown that a gap in this area can be filled particularly easily and reliably by material of the blocking layer, in particular by utilizing capillary forces.

Furthermore, a method for producing a radiation detector is specified.

In accordance with at least one embodiment of the method, a housing is provided. A semiconductor device is disposed in the housing. A gap between the housing and the semiconductor device is filled with a blocking layer.

The filling of the intermediate space takes place, for example, by means of a dispenser or a jetting ("ink-jet") method.

The blocking layer is thus formed only after the semiconductor device has already been arranged in the housing. It has been found that such a method is more cost-effective than a method in which semiconductor components for forming housings with a molding compound which forms the housing body, are transformed. In addition, the finite positioning accuracy in the positioning of the semiconductor devices and also in the casting methods used would cause a reduction in the useful radiation-sensitive area, thereby reducing the overall signal.

In accordance with at least one embodiment of the method, a material of the blocking layer is metered with respect to its quantity during filling of the intermediate space such that the intermediate space is completely filled and a radiation entrance surface of the semiconductor component remains free at least in places. In particular, the material of the blocking layer can be introduced in a cavity of the housing in plan view on exactly one side of the semiconductor component, wherein the material thereof, in particular, completely distributed around the semiconductor device around. For example, the filling takes place on one side of the semiconductor component, on which the housing has at least one connection surface for the electrical contacting of the semiconductor component, for example via a wire bond connection. In particular, a filling point in the production is laterally offset from the wire bond connection.

According to at least one embodiment of the method, the gap is filled along three side surfaces of the semiconductor device due to capillary forces. Thus, a radiation detector can be produced, which is characterized on the one hand by a compact design and on the other hand in a simple and reliable way suppresses a lateral radiation injection into the semiconductor device or at least reduced.

The method described is particularly suitable for the production of a radiation detector described above. In the context of the radiation detector mentioned features can therefore be used for the process and vice versa.

• 1 ein Ausführungsbeispiel für einen Strahlungsdetektor in schematischer Schnittansicht;
• 2 eine schematische Darstellung eines Referenzdetektors;
• 3A, 3B und 3C ein Ausführungsbeispiel für einen Strahlungsdetektor in schematischer Schnittansicht (3A) entlang der in der Draufsicht der 3B gezeigten Linie AA‘ und in perspektivischer Darstellung in 3C;
• 4 Messungen eines normierten Photostroms I_N in Abhängigkeit von der Wellenlänge A der auftreffenden Strahlung für einen Strahlungsdetektor und einen Referenzdetektor; und
• 5A, 5B, 5C und 5D ein Ausführungsbeispiel für ein Verfahren zur Herstellung eines Strahlungsdetektors anhand von schematisch in Schnittansicht dargestellten Zwischenschritten.

Further embodiments and expediencies will become apparent from the following description of the embodiments in conjunction with the figures.
Show it:

• 1 an embodiment of a radiation detector in a schematic sectional view;
• 2 a schematic representation of a reference detector;
• 3A . 3B and 3C An embodiment of a radiation detector in a schematic sectional view ( 3A ) along the in plan view of 3B shown line AA 'and in perspective in 3C ;
• 4 Measurements of a normalized photocurrent I _N as a function of the wavelength A of the incident radiation for a radiation detector and a reference detector; and
• 5A . 5B . 5C and 5D An embodiment of a method for producing a radiation detector based on intermediate steps schematically shown in sectional view.

The same, similar or equivalent elements are provided in the figures with the same reference numerals.

The figures are each schematic representations and therefore not necessarily to scale. Rather, comparatively small elements and in particular layer thicknesses may be exaggerated for clarity.

In 1 an embodiment for a radiation detector is shown in a schematic sectional view.

The radiation detector 1 has a semiconductor device 2 on. By way of example, the semiconductor component is an unhoused semiconductor chip, for example in the form of a photodiode or a phototransistor. A photosensitive region of the semiconductor device is based on a semiconductor material, such as silicon, or another semiconductor material, such as a III-V compound semiconductor material or a II-VI compound semiconductor material.

The semiconductor device 2 has a radiation entrance surface 20 on. In the lateral direction is the semiconductor device 2 through side surfaces 21 limited.

The semiconductor device 2 is in a cavity 35 a housing 3 arranged. A gap 33 between the case 3 and the semiconductor device 2 is with a blocking layer 5 filled. In particular, the blocking layer covers 5 the side surfaces 21 of the semiconductor device 2 Completely.

The housing 3 For example, is a prefabricated housing, wherein the radiation detector 1 is designed as a surface mountable device. Details of a possible embodiment of the housing 3 are in the 3A to 3C shown.

The radiation entrance surface 20 is completely or at least substantially completely free of material of the blocking layer 5 , Radiation coupling via the radiation entrance surface 20 is not or not substantially suppressed by the blocking layer.

The radiation detector is for detecting a signal radiation 8th provided, for example in the visible, infrared or ultraviolet spectral range.

On the radiation entrance surface 20 incident radiation, represented by arrows 80 , may enter the semiconductor device and provide a contribution to the signal there. For the adaptation of the spectral sensitivity of the semiconductor device 2 is on the radiation entrance surface 20 optionally a filter 4 arranged, for example in the form of a dielectric filter.

Signal radiation, the side of the radiation entrance surface 20 passing by and through a side surface 21 of the semiconductor device 2 could be coupled by an arrow 81 illustrated.

This radiation component is due to the blocking layer 5 prevented from radiation. Furthermore, a scattered radiation 9 shown by arrows, with an arrow 90 one on the radiation entrance surface 20 incident stray radiation shows. arrows 91 show a scattered radiation, at least partially over the side surfaces 21 of the semiconductor device 2 could be coupled if no blocking layer 5 would be provided.

The scattered radiation 9 typically hits the radiation detector in a larger angular distribution 1 on as the signal radiation, so that through the side surfaces 21 coupled radiation component for the scattered radiation is greater than the signal radiation. In addition, this laterally entering radiation portion of the filter 4 pass laterally, so that the radiation would also contain more unwanted spectral components for which the filter has no or only a small transmission.

The blocking layer 5 thus prevents lateral radiation entry into the semiconductor device 2 ,

The blocking layer 5 continues to border on a side surface 41 of the filter. A lateral radiation entry into the filter and a possible associated beam path into the semiconductor component can thus be avoided.

Thus, the unwanted radiation coupling of infrared radiation is essentially confined to radiation incident at large angles to the normal of the filter and due to the angular dependence of the filter can pass the filter.

For comparison purposes is in 2 a reference detector is shown which does not have such a blocking layer 5 having. In this reference detector, an increased radiation coupling can take place via the side surfaces of the semiconductor component. A lateral radiation coupling could be reduced by an increase in the vertical extent of the housing and / or the smallest possible distance between the semiconductor device and the housing. However, perpendicularly incident and reflected or scattered radiation within the housing could still enter through the side surfaces of the semiconductor device.

In 4 are shown measurement results of a normalized photocurrent I _{N of} the radiation detector, wherein a measurement curve 71 a measurement on a radiation detector and a reference curve 72 a measurement on a reference detector without a blocking layer 5 demonstrate. The measurement curves thus illustrate the respective spectral sensitivities of the detectors.

In the embodiment shown, the signal radiation is in a wavelength range having a peak wavelength of about 550 nm and a full half width of 35 nm. Such signal radiation is suitable, for example, for a pulse measurement, as for example in so-called fitness trackers on a wrist can be done.

Of course, the signal radiation 8th also have a different peak wavelength, in particular in the visible spectral range. Furthermore, the signal radiation can also be spectrally broadband, for example in the entire visible spectral range. For example, in this case the radiation detector is designed as an ambient light sensor.

The filter 4 is formed in the embodiment shown as a bandpass filter, which transmits radiation in the visible spectral range. For wavelengths above the cut-off wavelength of the bandpass filter at about 650 nm, the normalized photocurrent I _{N of} the measurement curve drops 71 significantly stronger than the normalized photocurrent I _{N of} the reference curve 72 , The over the wavelength range above 650 nm to the cut-off wavelength of the semiconductor device 2 lying integrated signal component is at the radiation detector by a factor 8th smaller than the corresponding signal component for the reference detector.

The measurements thus prove that unwanted signal components can be suppressed particularly efficiently by means of the described blocking layer, which is spectrally broadband-absorbing for the present measurement, in particular radiation components due to infrared radiation from the environment. With a fitness tracker, this radiation results, for example, from the wrist on which the fitness tracker is worn. The optical noise, in particular in the infrared spectral range, is thus efficiently suppressed without the need to reduce the photosensitive area of the radiation receiver for this purpose. This results in a better signal-to-noise ratio. Furthermore, it can be avoided with the blocking layer that metal layers arranged on the side of the semiconductor component, for example for electrical contacting, are visible from the outside.

In the 3A to 3C an embodiment of a radiation detector is shown, in particular details of a housing 3 are shown. Incidentally, the statements in connection with the exemplary embodiment in 1 , The housing 3 has a housing body 30 and external contacts 31 on. The external contacts 31 are formed, for example, by a lead frame, which is from the housing body 3 is formed, for example by an injection molding or transfer molding process.

The radiation detector 1 is formed as a surface mountable device, wherein the external contacts 31 on a mounting surface 10 of the radiation detector are available.

The semiconductor device 2 is from its the radiation entrance surface opposite back with her one of the external contacts 31 connected. Via a connecting line 39 represented in 3C , the semiconductor device is from its front side with another external contact 31 connected in an electrically conductive manner, for example with a connection surface of the further external contact arranged in the housing. Of course, the specific configuration of the housing and the type of electrical contacting of the semiconductor device within the housing and the electrical contact of the radiation detector per se can be varied within wide limits.

The cavity 35 is still with a casting 6 filled, such as a polymeric material such as a silicone or an epoxy. The casting 6 is formed in particular radiation-permeable to the signal radiation. The potting completely covers the blocking layer. The blocking layer and the casting border directly on each other. The potting immediately adjoins the filter 4 at. Seen in the vertical direction, the blocking layer runs in places between the potting 6 and the housing 3 , The connection line 39 runs at least in places within the casting 6 , Furthermore, the potting covers 6 the semiconductor device 6 Completely.

A lateral distance between the semiconductor device 2 and the housing 3 is at three side surfaces of the semiconductor device between 50 microns inclusive and including 200 microns. With such a dimensioning of the lateral distance, in the production of the radiation detector, the material for the blocking layer can be in only one place in the cavity 35 be introduced, wherein capillary forces cause the spaces between the semiconductor device 2 and the housing 3 can be completely filled.

In the 5A to 5D is an embodiment of a method for producing a radiation detector shown by intermediate steps shown schematically in sectional view.

A housing 3 with a cavity 35 will be provided ( 5A ). A semiconductor device 2 , optionally with a filter 4 is placed in the housing ( 5B ). The semiconductor device is connected to external contacts of the housing 3 electrically connected (in 5B not explicitly shown).

A gap 33 between the housing and the semiconductor device is provided with a blocking layer 5 filled. Preferably, a material of the blocking layer is metered in its amount so that the gap 33 is completely filled and a radiation entrance surface 20 the semiconductor device remains free at least in places. For example, the filling takes place by means of a dispenser or by means of a jetting method. A jetting process is particularly suitable since small quantities of material in droplet form can be metered with high accuracy.

When filling the gap, the gap may be filled along three side surfaces of the semiconductor device due to capillary forces. The filling is simplified. Below, as in 5D shown a potting 6 be formed.

With the described method, a radiation detector can be produced in a simple and reliable manner, which is characterized by a particularly high signal-to-noise ratio and at the same time is easy to produce.

The invention is not limited by the description with reference to the embodiments. Rather, the invention encompasses any novel feature as well as any combination of features, which in particular includes any combination of features in the patent claims, even if this feature or combination itself is not explicitly stated in the patent claims or the exemplary embodiments.

LIST OF REFERENCE NUMBERS

1

radiation detector

10

mounting surface

2

Semiconductor device

20

Radiation entrance area

21

side surface

3

casing

30

housing body

31

external contact

33

gap

35

cavity

39

connecting line

4

filter

41

side surface

5

blocking layer

6

grouting

71

measured curve

72

reference curve

8th

signal radiation

80

arrow

81

arrow

9

scattered radiation

90

arrow

91

arrow

Claims (15)

A radiation detector (1) for detecting a signal radiation (8) comprising a semiconductor component (2) and a housing (3) in which the semiconductor component is arranged, wherein a gap (33) between the semiconductor component and the housing is filled with a blocking layer (5) is. Radiation detector after Claim 1 wherein the blocking layer completely covers all side surfaces (21) of the semiconductor device. Radiation detector after Claim 1 or 2 wherein the blocking layer is impermeable at least to radiation between 700 nm and 1000 nm inclusive. A radiation detector according to any one of the preceding claims, wherein the blocking layer is opaque to the signal radiation. Radiation detector according to one of the preceding claims, wherein the blocking layer is impermeable to at least a part of radiation in the ultraviolet, for radiation in the visible and for a part of radiation in the infrared spectral region. A radiation detector according to any one of the preceding claims, wherein the blocking layer contains black pigments embedded in a matrix material. A radiation detector according to any one of the preceding claims, wherein the blocking layer contains carbon black. Radiation detector according to one of the preceding claims, wherein a radiation entrance surface (20) of the semiconductor device is at least locally free of the blocking layer. Radiation detector according to one of the preceding claims, wherein on the radiation entrance surface of the semiconductor device, a filter (4) is arranged and wherein the blocking layer adjacent to a side surface (41) of the filter. Radiation detector after Claim 9 wherein the filter is a bandpass filter that transmits radiation in the visible spectral range. Radiation detector according to one of the preceding claims, wherein a lateral distance between the semiconductor device and the housing at three side surfaces of the semiconductor device between 50 microns inclusive and including 200 microns. Method for producing a radiation detector with the steps: a) providing a housing (3); b) arranging a semiconductor device (2) in the housing; c) filling a gap (33) between the housing and the semiconductor device with a blocking layer (5). Method according to Claim 12 , wherein a material of the blocking layer in step c) is metered in terms of its amount so that the gap is completely filled and a radiation entrance surface (20) of the semiconductor device remains free at least in places. Method according to Claim 12 or 13 wherein the gap is filled along three side surfaces of the semiconductor device due to capillary forces. Method according to one of Claims 12 to 14 in which a radiation detector according to one of Claims 1 to 11 will be produced.

Images