SEMICONDUCTOR DETECTOR FOR TRACKING AND DETECTION OF SMALL OBJECTS

Abstract

A semiconductor detector for tracking of point-like sources comprises a plurality of pixels. The pixels are arranged in a rectangular lattice. Each pixel has a surface with a photosensitive region for detecting light. The photosensitive region has a geometric layout adapted to reduce a signal variation if the point source moves from a first pixel to a second pixel, wherein the second pixel is located at an adjacent lattice position with respect to the first pixel.

Claims

1. A semiconductor detector for tracking a point source, comprising a plurality of pixels arranged in a rectangular lattice, wherein each pixel has an area with a photosensitive region for detecting light, and wherein the photosensitive region has a geometric layout adapted to reduce a signal variation if the point source moves from a first pixel to a second pixel located at an adjacent lattice position with respect to the first pixel.

2. The semiconductor detector according to claim 1, wherein the geometric layout is adapted to reduce a difference of a first signal variation, occurring if the second pixel is located at a nearest-neighbor lattice position with respect to the first pixel, and a second signal variation, occurring if the second pixel is located at a second-nearest neighbor lattice position with respect to the first pixel.

3. The semiconductor detector according to claim 1, wherein the photosensitive region comprises a component with at least one of the following shapes: a diamond shape, a triangular shape, a kite shape, a star shape, an annulus with or without a spared sector, a polygonal ring with or without a spared sector.

4. The semiconductor detector according to claim 1, wherein the photosensitive region comprises a plurality of rectangles arranged in a rectangular grid.

5. The semiconductor detector according to claim 1, wherein a surface of each pixel comprises an area which is non-sensitive to light and comprises electronics configured to perform a readout of a signal generated by an illumination of the photosensitive region.

6. A missile warning device comprising a semiconductor detector, the semiconductor detector comprising: a plurality of pixels arranged in a rectangular lattice, wherein each pixel has an area with a photosensitive region for detecting light, and wherein the photosensitive region has a geometric layout adapted to reduce a signal variation if a point source moves from a first pixel to a second pixel located at an adjacent lattice position with respect to the first pixel.

7. A method for manufacturing a semiconductor detector for tracking a point source, the semiconductor detector comprising a plurality of pixels arranged in a rectangular lattice, the method comprising: generating, in each pixel, a photosensitive region which has a geometric layout adapted to reduce a signal variation if a point source illumination moves from a first pixel to a second pixel which is located at an adjacent lattice position with respect to the first pixel.

Description

BRIEF DESCRIPTION OF THE FIGURES

[0056] Various embodiments of the present invention will be described in the following by way of examples only, and with respect to the accompanying drawings, in which:

[0057] FIG. 1 shows different shapes of photosensitive areas of pixels of a semiconductor detector with the same fill factor according to the present invention, and their effect on signal variations.

[0058] FIG. 2 illustrates another embodiment of the semiconductor detector having pixels with the same fill factor.

[0059] FIG. 3 illustrates further embodiments of the semiconductor detector having pixels with the same fill factor.

[0060] FIG. 4 shows further embodiments of the semiconductor detector where the photosensitive region is subdivided in a checkerboard layout having pixels with the same fill factor.

[0061] FIG. 5 illustrates an effect of the size of a point source illumination.

[0062] FIG. 6 shows pixels of further embodiments where a geometric layout of a photosensitive region has a rectangular ring shape.

[0063] FIG. 7 shows four pixels of a conventional semiconductor detector.

[0064] FIG. 8 illustrates a horizontal and a diagonal movement of a point object illumination.

[0065] FIG. 9 shows two examples of a signal variation in a conventional semiconductor detector.

[0066] FIG. 10 shows two further examples of a signal variation in a conventional semiconductor detector with a larger spot.

DETAILED DESCRIPTION

[0067] Various examples will now be described more fully with reference to the accompanying drawings in which some examples are illustrated. It should be understood that there is no intent to limit examples to the particular forms disclosed, but on the contrary, examples are to cover all modifications, equivalents, and alternatives falling within the scope of the disclosure as defined by the subsequent claims and the description.

[0068] FIG. 1 shows photosensitive areas 13 of pixels 10 and corresponding signal variations for a semiconductor detector configured for tracking a point source illumination 20 (not depicted). The semiconductor detectors comprise a plurality of pixels 10 arranged in a rectangular lattice, wherein each pixel 10 comprises a photosensitive region 13 for detecting light and a non sensitive region 15 which may e.g. contain passive and active electronic components.

[0069] Organized in three rows from top to bottom, the figure displays three geometric layouts of a photosensitive region 13 in a pixel 10 of the same fill factor.

[0070] The first row of the figure shows a geometric layout of the photosensitive region 13 of a pixel 10 in a conventional semiconductor detector. This row is displayed to facilitate comparison.

[0071] The second and the third row of the figure show a geometric layout of the photosensitive region 13 adapted to reduce the signal variation in an embodiment of the semiconductor detector according to the present invention.

[0072] In the second and the third row, the photosensitive region 13 comprises a geometric layout adapted to suppress a signal variation if the point source illumination 20 moves from a first pixel 10 to a second pixel 10 which is located at a horizontal or vertical adjacent lattice position (pixel 10b or 10c in FIG. 8) or at a diagonal position (pixel 10d in FIG. 8) with respect to the first pixel 10 (10a in FIG. 8).

[0073] On the right of each displayed pixel 10, 110, the figure shows two diagrams which show a variation of intensities I1, 12, 13, It, in relative units over a distance, when a point source passes from a first pixel 10 to a second pixel 10. The diagrams refer to embodiments where the geometric layout of the photosensitive region 13 is the same for the first pixel 10 and the second pixel 10. In each row, a left diagram illustrates the signal variation if the second pixel 10 is located at a nearest neighbor position of the first pixel 10 in the rectangular (here, square) lattice (cf. the “horizontal” movement B1 in FIG. 8). Furthermore, in each row, a right diagram illustrates the signal variation if the second pixel 10 is located at a second-nearest neighbor position of the first pixel 10 in the rectangular lattice (cf. the “diagonal” movement B2 in FIG. 8).

[0074] In each row, the pixel 10 has a fill factor (i.e., a ratio of an area of the photosensitive region to the total area of the surface of the pixel) of about 0.2. The point source illumination 20 corresponds to a point spread function which has a diameter (based on locations with an intensity of 1/e.sup.2 times the maximal intensity) corresponding to about 95% of a pixel pitch, wherein the pixel pitch is a distance between centers of two pixels 10 which are nearest neighbors in the lattice.

[0075] Each diagram shows a first intensity I1, measured in the first pixel 10, a second intensity 12, measured in the second pixel 10, and a total density It, which is a sum of the intensities of all pixels 10 in the semiconductor detector. In each row, the respective right-hand diagram further shows the intensity measured by the pixels 10 immediately to the right and immediately above the first pixel 10 (cf. pixel 10c and 10b in FIG. 8), which for the diagonal movement B2 can provide a significant contribution to the total intensity.

[0076] For the horizontal movement B1, the ratio of a maximal value over a minimal value of the total intensity It decreases from 2.631 in the top row over 1.507 in the middle row to 1.436 in the bottom row.

[0077] For the diagonal movement B2, the ratio of a maximal value over a minimal value of the total intensity It decreases from 6.920 in the top row over 2.252 in the middle row to 1.673 in the bottom row.

[0078] In all three cases the diagonal movement B2 leads to a higher signal variation than the horizontal movement B1. With decreasing signal variation, the signal approaches more and more the theoretical value corresponding to the fill factor (here 20%).

[0079] Furthermore, in the top row the signal variation is strongly dependent on the direction of the movement B1, B2, with a quotient of the two ratios being 2.63. The analogous quotient in the middle row is only 1.49, and the analogous quotient in the bottom row is merely 1.17. This means that the signal variation becomes more and more independent from the direction of the spot movement from top to bottom row in FIG. 1.

[0080] Thus the geometric layout of the photosensitive region in the second and the third row is adapted to reduce a signal variation if the point source moves from a first pixel to a second pixel which is located at an adjacent lattice position with respect to the first pixel, while at the same time reducing a difference between a first signal variation, occurring for a movement B1 between two nearest neighbor pixels 10, and a second signal variation, occurring for a movement B2 between two second-nearest neighbor pixels 10.

[0081] FIG. 2 illustrates another embodiment of the semiconductor detector with a different geometry of the photosensitive region 13. In a top row, the figure shows again data for a conventional pixel 10 with a comparable fill factor for comparison. The bottom row shows an embodiment with a star-shaped photosensitive area 13. In both cases the fill factor has a value of about 0.3. The point source illumination diameter (measured as a maximal distance between two locations where the point spread function has dropped to 1/e.sup.2 times of the maximal value) covers about 65% of the pixel pitch. There are two diagrams in each row; a left diagram shows intensities for the horizontal movement B1 of the point source illumination, and a right diagram shows intensities for the diagonal movement B2 of the point source illumination 20.

[0082] In the top row, a ratio between a maximal and a minimal value of the total intensity It is 5.208 for the horizontal movement B1, and 27.127 for the diagonal movement B2. In the bottom row, the corresponding ratios are 5.266 and 6.900. Again, a measure for the difference between the signal variations for movements in the horizontal direction and in the diagonal direction is the quotient of these ratios. In the top row, this quotient is 5.2. In the bottom row, the quotient is 1.3, i.e., the difference in signal variations along the two different directions is reduced for the embodiment in the bottom row.

[0083] FIG. 3 illustrates further embodiments of the semiconductor detector with a different geometry of the photosensitive region 13. In a top row, the figure shows again data for a conventional pixel 10 with an equal fill factor for comparison. The middle row shows an embodiment with a photosensitive area 13 composed of four triangles. The bottom row shows an embodiment with a quadratic ring with four spared sectors. In all cases the fill factor is roughly 0.2. The point source illumination diameter (measured as a maximal distance between two loci where the point spread function has dropped to 1/e.sup.2 times a maximal value) covers about 80% of the pixel pitch.

[0084] In the top row, the horizontal movement B1 leads to a ratio between a maximal and a minimal value of the total intensity of 4.523. The diagonal movement B2 has an analogous ratio of 20.453. The quotient of these ratios is about 4.52.

[0085] In the middle row, the horizontal movement B1 leads to a ratio between a maximal and a minimal value of the total intensity of 2.595. The diagonal movement B2 has an analogous ratio of 6.558. Therefore, the quotient of these ratios is merely 2.53.

[0086] In the bottom row, the horizontal movement B1 leads to a ratio between a maximal and a minimal value of the total intensity of 1.162. The diagonal movement B2 has an analogous ratio of 1.489. The quotient of these ratios is about 1.28. In this row, the diagram corresponding to the diagonal movement B2 shows a difference between the intensity I5 measured by the pixel 10 directly above the first pixel 10 and the intensity I4 measured by the pixel 10 directly to the right of the first pixel 10.

[0087] For the diagonal movement B2, the minimum value of the total intensity is increased from less than 3% of the corresponding maximal value of the total intensity in the conventional geometry to a value of almost 15% in the embodiment depicted in the bottom row.

[0088] FIG. 4 shows a sequence of embodiments in which the photosensitive region 13 is subdivided into an increasingly small-scale checkerboard pattern. The fill factor is 0.5 in each case. For the diagrams on the right of each displayed pixel 10, the diameter of the point source illumination 20, again determined by a drop to 1/e.sup.2 times a maximal value of the corresponding point spread function, covers about 50% of the pixel pitch.

[0089] In this figure there are three diagrams in each row, i.e. for each embodiment. Of these diagrams, the diagram on the left illustrates the intensities I1, 12, It for the horizontal movement B1. The other two diagrams show intensities for a diagonal movement B2. Due to the asymmetry of the photosensitive region 13 in each of the pixels 10, a diagonal movement B1 in a bottom right direction (with respect to the respective pixel 10) generates a different intensity signal than a diagonal movement B2 in a top right direction. Thus, in the middle diagram, the point source 20 moves in the bottom right direction from the depicted pixel 10, while in the right diagram, the point source illumination 20 moves in the top right direction.

[0090] While this sequence shows that a mere increase of resolution within each pixel 10 theoretically leads to a stabilization of the total intensity It, various constraints to this approach must be kept in mind. The non-sensitive area 15 may comprise electronic components, in particular for memory capacity and for driving the pixel 10, which require a minimal space and an appropriate connection to each other. Depending on a pixel size and on the application, this puts a lower bound on the achievable subdivision. However, depending on the diameter of the point source illumination 20, the subdivision may be too coarse, in the sense that it will lead to undesired artifacts in the total intensity It for particular movements of the point source illumination 20.

[0091] Such a case may in particular be observed in the top row, where upon moving upwards and to the right (rightmost diagram in the top row), the point source illumination covers mainly the non-sensitive area 15, and the total intensity It artificially decreases to 10%. In contrast, when moving down and to the right (middle diagram), the point source illumination 20 crosses the tiles of the photosensitive region 13, and the signal increases by over 90%.

[0092] The finer the subdivision is chosen, the lower the amplitude of this effect becomes. In the third row from the top, a 6x6 subdivision causes the signal variation to disappear almost completely (the amplitude of the total intensity fluctuation is in a range of approximately 0.6% of a mean value). With an 8x8 subdivision (bottom row), no signal fluctuation can be detected anymore. However, depending on the physical size of the pixel 10, this subdivision may not be achievable.

[0093] FIG. 5 illustrates an effect of a size of the point source illumination 20 in an embodiment. The figure shows a pixel 10 with a photosensitive region 13 in the same geometric layout as in the top row of FIG. 4. The diagrams to the right of the pixel 10, arranged in the same way as in FIG. 4, show intensities for a point source illumination 20 covering 100% of the pixel pitch (as opposed to 50% in FIG. 4). In the diagonal movements B2, the total intensity It displays a variation of only about 16%.

[0094] From FIGS. 4 and 5, the person skilled in the art will readily observe that depending on a physical size of the pixels (and on the fill factor), on a pixel pitch, and on a size of expected illuminations, an optimal choice for the checkerboard photosensitive region may be achieved.

[0095] FIG. 6 shows pixels 10 of three further embodiments. In the pixel 10 on the left-hand side, the photosensitive region 13 has a shape of a rectangular ring. In the middle and on the right-hand side, the shape is interrupted by one and two spared regions, respectively. These spared regions may be utilized for charge carrier lines to and from electronic components, which may be located within the rectangular ring.

[0096] The description and drawings merely illustrate the principles of the disclosure. It will thus be appreciated that those skilled in the art will be able to devise various arrangements that, although not explicitly described or shown herein, embody the principles of the disclosure and are included within its scope.

[0097] Furthermore, while each embodiment may stand on its own as a separate example, it is to be noted that in other embodiments the defined features can be combined differently, i.e. a particular feature descripted in one embodiment may also be realized in other embodiments. Such combinations are covered by the disclosure herein unless it is stated that a specific combination is not intended.

[0098] Although the invention has been illustrated and described in detail by way of preferred embodiments, the invention is not limited by the examples disclosed, and other variations can be derived from these by the person skilled in the art without leaving the scope of the invention. It is therefore clear that there is a plurality of possible variations. It is also clear that embodiments stated by way of example are only really examples that are not to be seen as limiting the scope, application possibilities or configuration of the invention in any way. In fact, the preceding description and the description of the figures enable the person skilled in the art to implement the exemplary embodiments in a concrete manner, wherein, with the knowledge of the disclosed inventive concept, the person skilled in the art is able to undertake various changes, for example, with regard to the functioning or arrangement of individual elements stated in an exemplary embodiment without leaving the scope of the invention, which is defined by the claims and their legal equivalents, such as further explanations in the description.

TABLE-US-00001 LIST OF REFERENCE SIGNS 10, 10a, ... pixels 13 photosensitive region 15 non-sensitive area 20 point source B1 horizontal movement (between nearest neighbor pixels) B2 diagonal movement (between second-nearest neighbor pixels) I1, I2, ... intensities (measured by individual pixels) It total intensity