Image sensor

Abstract

An image sensor for an electronic camera has a plurality of pixels for generating exposure-related signals, wherein each pixel includes at least: a photosensitive element for generating charge from incident light; a readout node; a transfer gate for selectively coupling the photosensitive element to the readout node; a conversion transistor for converting charge present at the readout node into a voltage signal at a signal output terminal; and a selection switch connected to the signal output terminal of the conversion transistor for selectively coupling the signal output terminal of the conversion transistor to an assigned readout conductor of the image sensor. Each pixel has an electrically conductive shielding structure that at least partially surrounds the readout node and is set or can be set to a potential related to the voltage signal at the signal output terminal of the conversion transistor.

Description

Technical Field

[0001] The present invention relates to image sensors for electronic cameras, and more particularly to CMOS image sensors having a plurality of pixels for generating exposure-related signals. Background Art

[0002] Electronic cameras can be used, for example, as motion picture cameras to capture moving image sequences that are later shown in theaters. High image quality is crucial for these cameras. In particular, during post-processing, the brightness, contrast, and color of these captured images are modified. The final product (the processed moving image sequence or film) is then projected onto a large screen in a theater.

[0003] Electronic cameras typically use silicon image sensors using CMOS or CCD technology. When using this type of image sensor, pixels form the image area, and these pixels are arranged in rows and columns. These pixels can be provided with a color filter array (CFA) to have different spectral sensitivities. Each pixel includes at least: a photosensitive element for generating charge from incident light; a readout node; a transfer gate for selectively coupling the photosensitive element to the readout node and transferring the generated charge from the photosensitive element to the readout node; a wandler transistor for converting the charge present on the readout node into a voltage signal at a signal output; and a selector switch connected to the signal output of the wand transistor via an output conductor to selectively couple the signal output of the wand transistor to a designated readout conductor (e.g., a column conductor) of the image sensor. Therefore, the readout node of a pixel is generally formed by the connection between the output of the transfer gate and the input of the wand transistor (e.g., a gate contact).

[0004] The corresponding pixel may also include a reset switch to selectively couple the readout node to a reset potential. Such an image sensor may also include a control device for generating control signals for the corresponding transfer gate, the corresponding selection switch, and possibly the corresponding reset switch of the pixel to selectively read out the image signal (or the image signal and the reference signal) from the readout node. The conversion transistor may form an impedance converter that generates a voltage signal at its signal output terminal according to the amount of charge present at its input terminal. The readout conductors of the image sensor may be connected to corresponding readout amplifiers (e.g., column amplifiers, row amplifiers) to amplify the voltage signals of the pixels that are connected to the assigned readout conductors in turn. The multiple readout conductors of the image sensor may also be connected to a signal bus that leads to one or more output amplifiers to amplify the (possibly pre-amplified) voltage signals of the multiple readout conductors.

[0005] The pixels of the image sensor can be addressed, for example, row by row, and the signals of the pixels are directed to readout amplifiers at the edge of the image area and from there to an output, where they are digitized and optionally combined with correction data.

[0006] In order to be able to capture moving image sequences also under low light conditions and to keep the costs of artificial lighting means for film sets low, it is desirable for the image sensors of electronic cameras to have a high light sensitivity. Summary of the Invention

[0007] An object of the present invention is to provide an image sensor with better photosensitivity.

[0008] The present invention is based on the following considerations.

[0009] Photosensitivity is primarily determined by image sensor noise. Image sensor noise primarily consists of the noise of the corresponding pixels and the noise of the readout path. With appropriate design, the readout path noise can be reduced to, for example, 80 μV, making it only a minor influence compared to the pixel noise of, for example, 180 μV.

[0010] The noise voltage in a pixel is primarily determined by the switching transistor (e.g., source follower (SF)). Pixel noise is the ratio between the signal voltage caused by electrons and the noise voltage of the switching transistor (SF). Therefore, to reduce this noise, either the noise voltage of the switching transistor must be reduced or the signal voltage caused by electrons must be increased.

[0011] When a photon is absorbed in a photosensitive element (such as a PIN diode), an electron is generated there. The electron is transferred (wherein, during the readout process, a plurality of electrons generated by a photoelectric method are generally transferred) to a readout node (for example, a floating diffusion (FD)) by instantaneous control of the transfer gate of the pixel. The charge of the corresponding electron acts on the capacitance of the readout node (FD) and causes a voltage change there. The capacitance of the readout node mainly refers to the parasitic capacitance. The voltage change caused by the corresponding electron is inversely proportional to the capacitance of the readout node. In order to increase the signal voltage caused by the electron and thereby reduce the noise of the pixel, it is also possible to try to reduce the capacitance of the readout node (FD).

[0012] In a typical image sensor, the readout node of a corresponding pixel may have a capacitance of, for example, 1.6 fF (microfarads), thereby achieving a voltage change of 100 μV per electron. The capacitance of the readout node (FD) mainly consists of three components:

[0013] a) Capacitance of the FD-region;

[0014] b) the capacitance of the input (gate) of the switching transistor (SF); and

[0015] c) The capacitance of the connection from the readout node (FD) to the input (gate) of the switching transistor.

[0016] In the past few years, the capacitance a) of the FD region has been further reduced by lower implantation doses and therefore only accounts for a minor proportion of, for example, 0.12 fF (corresponding to 7.5%) in the capacitance of the read node (FD).

[0017] In a source follower transistor, the capacitance b) at the input of the conversion transistor consists of a gate-drain capacitance and a gate-source capacitance. The gate-drain capacitance is mainly caused by the overlap of the gate and drain contacts and can reach 0.24 fF in the case of a source follower transistor of a given size of 0.8 μm x 1.1 μm. The gate-source capacitance is composed of the sum of the capacitance of the gate area and the capacitance overlapping with the source contact and can nominally reach, for example, 3.1 fF in the case of a source follower transistor of a given size. Since the source contact of the source follower transistor is connected to the readout conductor (e.g., column conductor) when reading out the pixel, and the readout conductor follows the charge or corresponding voltage on the readout node (FD), only a part of the source capacitance is effective. In the case of a voltage gain (Gain) of the source follower transistor of, for example, 92.3%, only 7.7% of the source capacitance is effective, which corresponds to an effective gate-source capacitance of 0.24 fF. In this example, the total effective capacitance b) of the input (gate) of the switching transistor (SF) therefore amounts to 0.48 fF, which corresponds to 30% of the total capacitance of the readout node (FD).

[0018] The capacitance c) of the connection from the readout node (FD) to the input (gate) of the transfer transistor can generally be given a value of 1 fF and therefore dominates the typical capacitance of the readout node (FD) (1.6 fF) with a contribution of 62.5%.

[0019] Therefore, in order to significantly improve the sensitivity of the image sensor, the capacitance of the connection from the readout node (FD) to the input terminal (gate) of the conversion transistor must be reduced because this capacitance has the largest contribution to the capacitance of the readout node (FD).

[0020] This object is achieved by an image sensor having the features of the claims.

[0021] According to the present invention, in an image sensor of the type described, it is provided that the corresponding pixel has an electrically conductive shielding structure, which at least partially surrounds the readout node of the pixel and is set or can be set to a potential related to the voltage signal of the conversion transistor.

[0022] On the one hand, the shielding structure is continuously or at least temporarily at a potential that varies in accordance with the potential at the signal output terminal of the conversion transistor of the corresponding pixel. On the other hand, the shielding structure is arranged close to the readout node of the pixel. In particular, during the period when the selection switch is closed, and in particular, also before the selection switch is closed, while the readout node is being filled with charge from the photosensitive element, the shielding structure can be set to a potential corresponding to the voltage signal of the conversion transistor.

[0023] In particular, with reference to a top view of the corresponding pixel, the shielding structure at least partially surrounds the readout node of the pixel. The shielding structure may be at least partially disposed in a plane in which the readout node is located, so as to partially or completely surround the readout node (or a portion of the readout node). Alternatively or additionally, the shielding structure may be at least partially disposed in a plane offset relative to the plane of the readout node and proximate to the readout node, so as to partially or completely surround the readout node (or a portion of the readout node).

[0024] Thus, the shielding structure can cause the potential around the readout node (particularly around the connection from the output of the transfer gate to the input (gate) of the transfer transistor) to follow the potential of the signal output of the transfer transistor, which is related to the charge in the readout node. As a result, the base point (Fuβpunkt) of the capacitor formed by the capacitance of the readout node is raised in response to the charge present in the readout node. This reduces the potential difference and the effective capacitance of the readout node (FD). Consequently, the signal voltage caused by the electrons in the readout node is increased.

[0025] In other words, due to the shielding structure, the potential around the readout node at least temporarily follows the voltage generated at the signal output of the transfer transistor, which in turn is related to the charge accumulation in the readout node. As a result, the vast majority of the (parasitic) capacitance of the readout node is ineffective. With reference to the aforementioned exemplary values, in the case of a gain (Gain) of, for example, 92.3% of the transfer transistor or source follower transistor, this means that when the capacitance of the connection from the readout node (FD) to the input terminal (gate) of the transfer transistor is 1 fF, only 0.077 fF is effective.

[0026] By embedding the connection from the readout node to the input of the transfer transistor in the shield structure, the nominal capacitance is increased from 1 fF to 2 fF, due to the small distance to the surrounding shield structure. However, taking this effect into account, the effective capacitance is also significantly reduced, due to the connection of the shield structure to the potential of the signal output of the transfer transistor, which reaches, for example, 0.144 fF (= 2 x 0.077 fF).

[0027] As a result, the total effective capacitance of the readout node of a pixel with a shielded structure can be reduced from 1.6 fF to 0.744 fF (= 0.12 fF + 0.48 fF + 0.144 fF), or 46.5% of the output value, in the example given above. The signal voltage caused by electrons can thus be increased from 100 μV to 215 μV. As a result, the noise is effectively reduced by more than half, from 1.6 electrons (160 μV noise at 100 μV / e-) to 0.75 electrons. This significant reduction in noise leads to a significant improvement in light sensitivity.

[0028] It should be understood that the above values ​​are exemplary only and the effect achieved by the shielding structure may be stronger or weaker.

[0029] The present invention can also be used with more complex pixel architectures and / or readout architectures than those mentioned above. For example, in the corresponding pixel, the overflow capacitor Additional transfer gates may be provided, which will be further described below. In some embodiments, the corresponding pixel may have a unique photosensitive element; in some other embodiments, the corresponding pixel may also have multiple photosensitive elements, which are coupled to a common readout node (FD) via corresponding transfer gates (so-called "sharing") and / or the multiple photosensitive elements are assigned (temporally alternating) to a common conversion transistor. Furthermore, the image sensor for each column or row of pixels may have multiple readout conductors (for example, multiple column conductors for each column of pixels), or multiple channels for each pixel. There are different gain factors set.

[0030] When considering voltage or potential in conjunction with the present invention, it should be noted that voltage is defined as the difference between a first potential (e.g., a generated or observed potential) and a second potential (e.g., a reference potential). In this regard, the two terms can ultimately have the same meaning or be used synonymously, as long as the corresponding reference potential is given.

[0031] When referring to conductive lines in an image sensor in conjunction with the present invention, an electrically conductive connection is to be understood as meaning that the electrically conductive connection can be formed in particular on or in the substrate (for example by metallization or doping).

[0032] Other embodiments of the present invention will be described below.

[0033] In some embodiments, the shielding structure can be permanently connected to the signal output (e.g., source terminal) of the transfer transistor. In other embodiments, the shielding structure can only be temporarily coupled to the signal output of the transfer transistor (in particular, by temporarily closing an associated switch). In this case, the shielding structure can be selectively coupled to the signal output of the transfer transistor at least during the closing of the select switch of the corresponding pixel, and in particular also before the select switch is closed, i.e., during the filling of the readout node with charge from the photosensitive element via the transfer gate. A control device of the image sensor (e.g., an internal or external microcontroller) can be configured to control the switches of the image sensor in a corresponding sequence.

[0034] In the above case, the shielding structure can be connected or coupled directly or indirectly to the signal output of the switching transistor. The direct connection or coupling can be formed in particular by a continuous electrical conductor within the corresponding pixel. The indirect connection or coupling to the signal output of the switching transistor can be realized, for example, by a distributed impedance transformer and / or by other (in particular active) electronic components, which will be explained further below.

[0035] For example, the shielding structure can be connected directly (in particular via a connecting line) to the signal output of the switching transistor, wherein such a connecting line extends completely within the respective pixel or also partially outside the respective pixel.

[0036] In some embodiments, the selection switch of the corresponding pixel can be connected to the signal output of the conversion transistor via an output conductor, wherein the shielding structure can be connected to the signal output of the conversion transistor via the output conductor (and optionally also via a connecting conductor leading to the output conductor), in particular only via a portion of the output conductor. As a result, a direct connection with a shorter conductor path is achieved to set the shielding structure to the potential of the signal output. In particular, a continuous connection is provided in these embodiments, but a switchable coupling is also generally possible. Preferred embodiments of compact pixel architectures will be further described below, in which embodiments, the connecting conductor between the shielding structure and the signal output of the conversion transistor extends completely within the corresponding pixel, and the readout node includes a bridge portion, which is surrounded by the shielding structure. In other embodiments, the shielding structure can be connected to or coupled to the signal output of the conversion transistor via a total output conductor (extending between the signal output of the conversion transistor and the selection switch), as will be explained below.

[0037] In some embodiments, the shielding structure can be coupled to the signal output of the conversion transistor at least via an assigned readout conductor (e.g. a column conductor or a row conductor) of the image sensor and a selection switch of the corresponding pixel. It is therefore also possible that the potential of the shielding structure follows the potential at the signal output of the conversion transistor via a connection extending outside the corresponding pixel. When the selection switch of the corresponding pixel is closed, the shielding structure can then be coupled to the signal output of the conversion transistor, in particular via the readout conductor. In particular, it can be provided that at this moment (i.e. when the selection switch of the corresponding pixel is closed to couple the signal output of the conversion transistor to the assigned readout conductor), the switches of the other pixels assigned to this readout conductor are not closed. Mutual influencing of the pixels can thereby be prevented, in particular when no further decoupling is provided between the shielding structure of the pixel and the assigned readout conductor.

[0038] In such embodiments, i.e., when the shielding structure is couplable to the signal output of the corresponding switching transistor via an associated readout line of the image sensor, the coupling can be achieved indirectly via an impedance transformer. This prevents the shielding structure from unintentionally increasing the capacitance of the readout line (e.g., column line) due to the connection of the associated pixel and from influencing the corresponding voltage signal of the switching transistor or its temporal behavior (e.g., oscillation duration).

[0039] Such a common impedance converter can be provided for each readout conductor (e.g., column conductor). The impedance converter can, for example, be provided at the edge of a pixel area. Thus, a corresponding impedance converter can be provided in particular for a plurality of or all pixels of a column. The input of the impedance converter can be connected to the readout conductor. Thus, the input of the impedance converter can further be connected to the input of a column readout circuit (e.g., a column amplifier circuit) or a row readout circuit. At least a portion of the connection line from the output of the impedance converter to the corresponding shielding structure can extend approximately parallel to, and in particular close to, the assigned readout conductor (e.g., column conductor), and can therefore also be used to decouple a plurality of adjacent readout conductors from each other during inactive times.

[0040] In some embodiments, the impedance converter may be configured as a voltage follower.

[0041] In some embodiments, the impedance converter can be configured to amplify the corresponding input signal (in particular the received voltage signal of the corresponding switching transistor) to increase the dependency of the potential of the shielding structure on the voltage signal of the switching transistor or on the amount of charge in the readout node (FD). Thus, the impedance converter can be used as a feedback amplifier. A particularly effective shielding effect can thereby be achieved. The impedance converter can comprise, for example, an amplification of approximately 108%, thereby resulting in a total amplification of approximately 100% in combination with, for example, an amplification of 92% of the switching transistor (SF). The amplification of the impedance converter or the feedback amplifier can also be optionally larger to compensate for the contribution of the additional capacitance of the readout node; however, the amplification cannot be too large so that the system does not become unstable and, for example, does not start to oscillate.

[0042] In some embodiments with an impedance converter, this type of amplification of the voltage signal of the corresponding switching transistor can be switchable, and / or the impedance converter can be configured to amplify the voltage signal of the switching transistor with a decaying amplification characteristic (i.e., with a decreasing ratio between the input signal and the output signal of the impedance converter). This allows better consideration of different exposure conditions or different charge levels in the readout node of the corresponding pixel, such that, for example, the potential of the shielding structure is increased to a greater extent in the case of a small charge level in the readout node (stronger correlation with the voltage signal at the output of the switching transistor, smaller capacitance of the readout node) than in the case of a larger charge level in the readout node.

[0043] In such embodiments having an impedance converter (particularly configured as an amplifier), connecting conductors can be provided between the output of the impedance converter and the corresponding shielding structure. Such connecting conductors can be switchable. In particular, it can be provided that the shielding structure is coupleable to the output of the impedance converter via a coupling switch, so that the shielding structure is selectively coupled to the output of the impedance converter. In this case, a first section of the connecting conductors for multiple pixels (e.g., multiple or all pixels in a column) can be shared, while a corresponding second section of the connecting conductors (between the corresponding coupling switch and the corresponding shielding structure) can be assigned to the corresponding pixel.

[0044] Generally, the shielding structure can be coupled directly or indirectly to the signal output of the corresponding conversion transistor via a coupling switch, so that the potential of the shielding structure only follows the voltage signal of the conversion transistor at appropriate or necessary times. In some embodiments, such a coupling switch can be controlled together with the selection switch of the corresponding pixel to selectively couple the shielding structure to the signal output. In particular, the coupling switch and the selection switch of the corresponding pixel can be connected to a common control line. Thus, in the case of simple control, it is possible that the shielding structure is connected only to the output of the impedance converter and acts as the desired shield, but also acts as a capacitive load when the voltage signal of the corresponding pixel is actually read out. Optionally, a separate control line for independent control can also be provided for the coupling switch. In all of the above cases, the control of the coupling switch can be achieved by the control device of the image sensor mentioned above, which also generates the necessary control signals for the corresponding transfer gate of the pixel, the corresponding selection switch, and possibly the corresponding reset switch.

[0045] In some embodiments, particularly when the shielding structure is directly or indirectly couplable to the signal output of the corresponding switching transistor via a coupling switch, the shielding structure can be couplable to a reference potential via an additional coupling switch. This allows the shielding structure to be at a predetermined, fixed potential when the additional coupling switch is closed, thereby preventing unintended effects on the pixel, and in particular, the readout node, due to undefined or floating potentials. In particular, the reference potential can be related to ground potential or the supply voltage of the image sensor.

[0046] In some embodiments, the image sensor and in particular the control device of the image sensor are configured such that the coupling switch and the additional coupling switch are only closed alternately with each other, so that the corresponding shielding structure is either only coupled (directly or indirectly) to the voltage signal of the conversion transistor or only coupled to the reference potential.

[0047] In some embodiments, the shield structure may surround the readout node on at least three sides. This can significantly reduce the effective capacitance of the readout node. The shield structure may surround the readout node on at least three sides within the arrangement plane where the readout node is located. In some embodiments, the shield structure may surround the readout node on four sides within the arrangement plane where the readout node is located. In some embodiments, the shield structure may surround the readout node on five or six sides, i.e., within the arrangement plane where the readout node is located, as well as on the upper side and / or lower side of the arrangement plane.

[0048] In some embodiments, the shield structure may be circumferentially closed to achieve a significant reduction in the effective capacitance to the readout node.

[0049] In some embodiments, the shielding structure may have an O-shape. In particular, the shielding structure may form a shielding ring.

[0050] In some embodiments, the shielding structure may be open in the circumferential direction (eg, by a slit or a specific opening), for example, to enable another electrical connection within the pixel by passing through the opening.

[0051] In particular, the shielding structure may have a C-shape or a U-shape.

[0052] In some embodiments, the shielding structure may extend in a plane, in particular, in the arrangement plane in which the readout nodes are also located. However, the shielding structure may also extend in a plane extending slightly above or below the arrangement plane in which the readout nodes are also located.

[0053] The shielding structure can be connected or coupled directly or indirectly to the signal output of the switching transistor via a connecting line, wherein at least a portion of the connecting line adjacent to the shielding structure extends approximately perpendicular to the extension plane of the shielding structure. This allows for a compact and efficient arrangement of the shielding structure.

[0054] In some embodiments, the shielding structure can be formed from metal strips. The shielding structure's electrical connection to the pixel's output conductor, which connects the signal output of the switching transistor to the associated selector switch, can also be formed from metal strips. Such metal strips can be formed using appropriate metallization during pixel fabrication.

[0055] In some embodiments, the shielding structure can consist of a trench ("active ground"), which is located, in particular, in the plane of the silicon surface or the plane of the semiconductor substrate used and can be permanently electrically conductive. The trench can, in particular, be directly connected to the signal output (e.g., source terminal) of the switching transistor.

[0056] In some embodiments, the respective pixel may have an additional electrically conductive shielding structure, which also at least partially surrounds the readout node and is set or can be set to a potential that is related to the voltage signal of the conversion transistor. Thus, the readout node of the respective pixel can be partially surrounded by a first shielding structure and partially surrounded by a second shielding structure, in particular in a mutually complementary arrangement, wherein the potential of the first shielding structure and the potential of the second shielding structure can be related to the voltage signal of the conversion transistor in different ways. As a result, a particularly robust shielding or a robust reduction in the capacitance of the readout node can be achieved. For example, the first shielding structure can be directly connected to the signal output of the conversion transistor, while the second shielding structure can be indirectly connected to the signal output of the conversion transistor, for example via the described impedance converter (in particular configured as an amplifier).

[0057] The shielding structure may be implemented in a compact pixel architecture in which the connection between the shielding structure and the signal output of the switching transistor is formed entirely within the respective pixel.

[0058] In some embodiments, the readout node may include a bridge portion connecting an output of a transfer gate to a gate terminal of a transfer transistor, wherein the transfer gate and the transfer transistor are located in a first plane of the pixel (particularly a substrate plane or a doping plane), and the bridge portion of the readout node is located in a second plane (particularly a metallization plane) that is offset parallel to the first plane, wherein the shielding structure includes a shield portion that is located in the second plane of the pixel and that at least partially surrounds the bridge portion of the readout node. In such an embodiment, when the shielding structure and thus the shield portion are set to a potential related to the voltage signal of the transfer transistor, a very effective shielding of the readout node and a reduction in the effective capacitance of the readout node can thereby be achieved in a sealed arrangement of the essential elements of the pixel.

[0059] In such an embodiment with a shielded, vertically offset bridge portion of the readout node, the bridge portion can be connected to the output end of the transfer gate via a first through-hole (Durchkontaktierung) extending perpendicularly to the first plane of the pixel, wherein the bridge portion can be connected to the gate connection of the conversion transistor via a second through-hole extending perpendicularly to the first plane of the pixel.

[0060] In such embodiments with a bridge portion of the readout node, the bridge portion may cross the signal output terminal of the switching transistor to further improve the shielding effect.

[0061] The bridge portion of the readout node can be formed by a metal strip on the semiconductor substrate, while the transfer gate and the conversion transistor of the pixel can be formed by a conductive channel in the semiconductor substrate (especially the transfer gate and the access channel of the conversion transistor, i.e., the source-drain connection).

[0062] In such embodiments with a bridge of the readout node, the shield may form a circumferentially closed ring which laterally encloses the bridge in the second plane of the pixel.

[0063] The shielding portion of the shielding structure extending in the second plane of the pixel may at least partially cover the output terminal of the transfer gate and the signal output terminal of the conversion transistor, so as to further improve the shielding effect.

[0064] The shielding portion of the shielding structure extending in the second plane of the pixel can be electrically connected to the signal output terminal of the conversion transistor through a through hole extending perpendicular to the first plane of the pixel.

[0065] In such an embodiment having a bridge portion of the readout node, in addition to the shielding portion extending in the second plane of the pixel, the shielding structure further includes at least one additional shielding portion extending in the first plane of the pixel and disposed proximate to the transfer gate and / or the conversion transistor. This can further enhance the shielding effect.

[0066] Such additional shielding parts may be formed as long fingers with free ends.

[0067] The additional shielding portion of the shielding structure may extend parallel to the pass channel of the switching transistor.Alternatively or additionally, the additional shielding portion is offset in parallel and extends in the same direction relative to a portion of the shielding portion located in the second plane of the pixel.

[0068] In some embodiments, the shielding structure may surround more than half of the shortest path extending from the output terminal of the transfer gate to the input terminal (gate contact) of the conversion transistor.

[0069] In some embodiments, the transfer transistor may be configured and coupled to the readout node such that a voltage signal generated at a signal output terminal (eg, a source terminal) of the transfer transistor is related to the charge present in the readout node.

[0070] In some embodiments, as described above, the image sensor may include a control device connected to at least the transfer gate and the selection switch of the corresponding pixel and configured to generate control signals for the transfer gate and the selection switch.

[0071] In some embodiments, the corresponding pixel may further include a reset switch to selectively couple the readout node to a reset potential. The control device is configured to further generate a control signal for the reset switch.

[0072] In some embodiments, the corresponding pixel may further include an overflow capacitor and an additional transfer gate to selectively couple the readout node to the overflow capacitor. This allows the capacitance of the readout node to be selectively temporarily increased to enable it to receive a large amount of charge from the photosensitive element during intense exposure. The control device may be configured to generate a control signal for the additional transfer gate.

[0073] In some embodiments, the assigned sense conductors may be connected or coupleable to sense amplifiers and / or to a signal bus leading to an output amplifier. BRIEF DESCRIPTION OF THE DRAWINGS

[0074] The present invention will be described below with reference to the accompanying drawings according to embodiments, wherein the same or similar elements are represented by the same reference numerals.

[0075] Figure 1A prior art four-transistor CMOS image sensor is shown, wherein only a pixel in the image sensor and a column readout circuit assigned to a column conductor of the pixel are shown;

[0076] Figure 2 To correspond to Figure 1 Schematic diagram showing an image sensor according to the present invention;

[0077] Figure 3 Shown according to Figure 2 an alternative embodiment of a corresponding pixel of an image sensor;

[0078] Figure 4 shows an equivalent circuit diagram with a capacitor according to Figure 2 an alternative embodiment of a corresponding pixel of an image sensor;

[0079] Figures 5 to 10 Shown according to Figure 2 Alternative embodiments of image sensors;

[0080] Figure 11 a top view showing a first plane of pixels of an image sensor; and

[0081] Figure 12 Shown according to Figure 11 A top view of a second plane of pixels.

[0082] Reference Signs List

[0083] 11 pixels

[0084] 15, 15a, 15b Photosensitive element

[0085] 17 columns of wires

[0086] 31 Power Supply

[0087] 33 Circuit Breaker

[0088] 39 transfer gate

[0089] 41 Readout Node

[0090] 42 Read out the parasitic capacitance of the node

[0091] 43 switching transistors

[0092] 44 Signal output terminal of conversion transistor

[0093] 45 Reset switch

[0094] 47 Selector switch

[0095] 51 Power supply voltage

[0096] 61, 61' shielding structure

[0097] 62 Capacitance of shielded structure

[0098] 63, 63' connecting wire

[0099] 66 Isolation distance

[0100] 71 Overflow Capacitor

[0101] 73 Additional transfer gate

[0102] 113 column readout circuit

[0103] 115 Precharge Circuit

[0104] 127 Reference value capacitor

[0105] 131 Amplifier

[0106] 133 Signal Value Capacitor

[0107] 135 positive input terminal

[0108] 137 Negative input terminal

[0109] 144 output wire

[0110] 147 Coupling switch

[0111] 149D, 149E switches

[0112] 153 Control Device

[0113] 160 Decoupling Circuit

[0114] 162 Impedance Converter

[0115] 163 connecting wires

[0116] 165 Ground potential

[0117] 166 Switch

[0118] 167 capacitors

[0119] 168 capacitors

[0120] 171 Additional coupling switch

[0121] 239 Transfer Gate Pass Channel

[0122] 240 Gate contact of transfer gate

[0123] 243 Pass channel of the switching transistor

[0124] 244 Gate connection of the switching transistor

[0125] 245 Reset switch gate connector

[0126] 247 Selector switch gate connector

[0127] 261 Additional shielding portion of shielding structure

[0128] 273 Additional gate contact for transfer gate

[0129] 317 Contact area for column conductors

[0130] 340 Contact area for transfer gate

[0131] 341 Reading the bridge portion of the node

[0132] 345 Contact area for reset switch

[0133] 347 Contact area for selector switch

[0134] 351 Contact wire for supply voltage

[0135] 352 Contact area for ground wire

[0136] 361 shielding part of shielding structure

[0137] 371 Overflow capacitor metallization

[0138] 373 Contact area for additional transfer gate DETAILED DESCRIPTION

[0139] The following will be combined Figure 1 The basic operating mode of an exemplary conventional four-transistor image sensor (active pixel sensor) of the APS type is described, wherein individual components of this image sensor may also be present in the image sensor of the present invention. In principle, the present invention is not limited to active four-transistor image sensors, but can also employ image sensors having fewer or more than four transistors per pixel, as will be explained further below.

[0140] exist Figure 1 , only a single pixel 11 is shown by way of example, comprising a single photosensitive element 15 in the form of a photodiode, in particular a so-called PIN diode. The photosensitive element 15 can be selectively charge-coupled via a switch in the form of a transfer gate 39 to a readout node 41, which is in particular designed as a so-called floating diffusion (FD).

[0141] The readout node 41 is connected to the gate terminal of a switching transistor 43 designed as a source follower, which is formed by a field effect transistor (FET) and represents a charge-voltage conversion circuit. Furthermore, the readout node 41 is connected to a (for example, positive) voltage source 51 via an additional switching device in the form of a reset switch 45. One of the two channel terminals of the switching transistor 43 (the drain terminal) is also connected to the positive voltage source 51, while the other of the two channel terminals of the switching transistor 43 (the source terminal) forms a signal output 44 at which a voltage signal is output and which is connected via an output line to a selection switch 47. The selection switch 47 functions as a row selection switch, wherein by activating or closing the selection switch 47, the signal output 44 of the switching transistor 43 can be selectively coupled to a readout line in the form of a column line 17, which is assigned to the pixel 11 shown.

[0142] Column conductors 17 are provided to connect pixels 11 of the same type arranged in an associated column to a common column readout circuit 113 , such as a column amplifier circuit. This is achieved by alternately temporarily closing the corresponding select switches 47 of the pixels 11 .

[0143] Column readout circuit 113 includes a first capacitor or reference value capacitor 127, which is connected to ground via one terminal and is selectively coupleable to column conductor 17 via switch 149E via another terminal. Column readout circuit 113 further includes a second capacitor or signal value capacitor 133, which is also connected to ground via one terminal and is selectively coupleable to column conductor 17 via an additional switch 149D via another terminal. Column readout circuit 113 further includes an amplifier 131, to which the voltage across first capacitor 127 is applied, at a negative input 137, and to which the voltage across second capacitor 133 is applied, at a positive input 135.

[0144] The transfer gate 39 of the corresponding pixel 11 can be controlled by the control wire TRF of the common control device 153 of the image sensor, the reset switch 45 can be controlled by the control wire RES of the common control device 153 of the image sensor, the selection switch 47 can be controlled by the control wire SEL of the common control device 153 of the image sensor, the switch 149E can be controlled by the control wire S1 of the common control device 153 of the image sensor, and the switch 149D can be controlled by the control wire S2 of the common control device 153 of the image sensor.

[0145] Furthermore, outside the pixel area of ​​the image sensor ( Figure 1The column conductor 17 is assigned a pre-charging circuit 115, which comprises a power supply 31 that can be selectively coupled to the column conductor 17 by means of a circuit breaker 33. The circuit breaker 33 is controlled by a common control device 153 via a control line S3.

[0146] The operating principle of such pixels 11 will be described below by way of example based on 3.3V CMOS technology. This method is also known as "Correlated Double Sampling" (CDS). Generally, all pixels 11 in a row can be read in the same manner, and in particular in parallel, so that it is sufficient to describe the readout process by focusing only on those pixels connected to the same column conductor 17.

[0147] First, during exposure, incident light is converted into charges by the photosensitive element 15, thereby filling the photosensitive element 15 with electrons. During exposure, the control lines TRF, RES and SEL are respectively kept at 0V, ie the switches 39, 45, 47 controlled thereby are open.

[0148] Before actual readout, circuit breaker 33 is closed in a pre-charge step (Pre-Charge). Then, after column conductor 17 is set to a given reference voltage (here, ground potential), circuit breaker 33 is opened. In parallel, a voltage of 3.3 V is momentarily applied to control line RES to remove charge from readout node 41 caused by leakage current and / or stray light, i.e., to clear readout node 41. As a result, readout node 41 is set to the reference value defined by voltage source 51. Consequently, a voltage corresponding to the cleared charge at readout node 41 appears at signal output 44 of transfer transistor 43.

[0149] In the next step (reading the reference value), a voltage of 3.3 V is applied to the control line SEL, closing the selector switch 47. First, the switch 149E is closed. As a result, the voltage value of the transfer transistor 43 corresponding to the charge at the readout node 41 is connected to the column line 17 via the selector switch 47 and, thus, is transferred to the capacitor 127. After the system oscillates, the selector switch 47 is reopened by a corresponding control signal, and the capacitor 127 is simultaneously disconnected from the column line 17 again due to the opening of the switch 149E.

[0150] Then, in the next precharging step, the column conductor 17 is re-precharged to a given reference potential by momentarily closing the circuit breaker 33. In parallel, a voltage of 3.3 V is momentarily applied to the control conductor TRF to momentarily open the transfer gate 39 or close the switch formed thereby, so that the electrons generated in connection with the exposure of the photosensitive element 15 can flow to the readout node 41.

[0151] In the next step (reading the signal value), the selection switch 47 and the switch 149D are closed. As a result, the voltage value of the conversion transistor 43 corresponding to the charge of the readout node 41 is connected to the column conductor 17 through the selection switch 47 and is thus transferred to the capacitor 133. After the system oscillates, the capacitor 133 is disconnected from the column conductor 17 again by opening the switch 149D. By applying 0V to the control line SEL, the selection switch 47 is also opened, and the pixel 11 is disconnected from the column conductor 17.

[0152] At this time, a voltage is applied to the output terminal of the amplifier 131 , which voltage corresponds to the difference between the voltage values ​​stored in the capacitors 127 , 133 and the amount of charge generated in the photosensitive element 15 as a result.

[0153] Finally, in a further next step, a voltage of 3.3 V is momentarily applied to the control conductor RES to remove the charge from the readout node 41 and ultimately remove the residual charge from the photosensitive element 15, so that the next exposure process can start again from a completely "empty" pixel 11.

[0154] These steps may also be performed on other pixels 11 connected to corresponding column conductors 17 .

[0155] Figure 2 A portion of an image sensor according to the present invention is shown, wherein a four-transistor image sensor is again schematically illustrated and only a single pixel 11 is schematically shown, although the image sensor has a plurality of pixels 11 arranged in rows and columns.

[0156] and Figure 1 The main difference is that the corresponding pixel 11 has an electrically conductive shielding structure 61 surrounding the readout node 41, wherein the shielding structure 61 is set to a potential related to the voltage signal of the conversion transistor 43. Figure 2 In the illustrated embodiment of the pixel 11 , the shielding structure 61 is connected via an electrically conductive connecting line 63 to the signal output 44 of the switching transistor 43 or to an output line that connects the signal output 44 of the switching transistor 43 to the selection switch 47 .

[0157] Therefore, shield structure 61 is disposed proximate to readout node 41 on multiple sides thereof, and particularly proximate to the connection from readout node 41 to the input terminal of transfer transistor 43. Shield structure 61 is not at a fixed potential. Because shield structure 61 is connected to transfer transistor 43 or signal output terminal 44 of pixel 11, the potential applied to shield structure 61 is in fact dictated by the potential or voltage signal at signal output terminal 44 of transfer transistor 43, which in turn is related to the charge accumulated in readout node 41.

[0158] This reduces the potential difference between the capacitors formed by the parasitic capacitance of readout node 41 and the capacitance of the shield structure surrounding readout node 41. Consequently, the effective capacitance of readout node 41 is also reduced. Consequently, the signal voltage caused by electrons generated by photosensitive element 15 in readout node 41 is increased. Consequently, the ratio between the signal voltage caused by the electrons and the noise voltage of conversion transistor 43 is improved. This reduces the noise of pixel 11 and improves photosensitivity.

[0159] like Figure 2 As shown in FIG, the shielding structure 61 can be circumferentially closed, in particular annular. The shielding structure 61 can be substantially O-shaped or designed as a polygon, for example.

[0160] Figure 3 An alternative embodiment is shown in which shield structure 61 is circumferentially open and surrounds sense node 41 on three sides. Shield structure 61 is generally U-shaped and is disposed around the connection from sense node 41 to the input of transfer transistor 43. However, shield structure 61 may also be generally C-shaped, for example. The U-shape or C-shape shown may also be oriented in other ways, such as with the open side of shield structure 61 facing toward transfer transistor 43 or toward reset switch 45.

[0161] In accordance with Figure 2 and Figure 3 In the embodiment of the present invention, the shielding structure 61 may be provided in a manner corresponding to Figure 2 and Figure 3 extends in the extension plane of, or parallel to Figure 2 and Figure 3 The extension plane of the shielding structure 61 may correspond to the arrangement plane in which the readout node 41 is also arranged. Alternatively, the extension plane of the shielding structure 61 may also extend slightly above or below the arrangement plane in which the readout node 41 is located.

[0162] In all of the above cases, the connecting conductor 63 or at least a portion of the connecting conductor 63 that is adjacent to the shielding structure 61 ( Figure 2 and Figure 3Schematic diagram is different), substantially perpendicular to the extension plane of the shielding structure 61 or perpendicular to Figure 2 3, so that the connecting line 63 can be kept short and the connecting line 63 can be better integrated into the existing structure of the pixel 11.

[0163] The shielding structure 61 and the connecting line 63 can be easily produced by metallization or by continuous-conducting trenches in the substrate used. Thus, the formation of the shielding structure 61 and the connecting line 63 can be easily integrated into the conventional manufacturing process of the pixel 11 .

[0164] Figure 4 The diagram shows that a shielding structure 61 may also be provided, for example in the case of a five-transistor image sensor. Figure 4 The corresponding pixel 11 additionally comprises an overflow capacitor 71 and an additional transfer gate 73. The additional transfer gate 73 can be controlled by the control device 153 (see Figure 2 ) is selectively controlled via control conductor TG2 so that readout node 41 is coupled to overflow capacitor 71. Thus, the capacitance of readout node 41 can be selectively and temporarily increased to be able to receive a large amount of charge generated in photosensitive element 15 under high exposure conditions for the pixel. As long as a high signal-to-noise ratio is achieved under high exposure conditions, the associated (temporary) increase in capacitance of readout node 41 does not adversely affect photosensitivity.

[0165] Figure 4 Also shown are the already mentioned (parasitic) capacitance of the readout node 41, which is shown in the equivalent circuit diagram as capacitor 42, and the capacitance of the shielding structure 61, which is shown as capacitor 62. The total effective capacitance of the readout node 41 is reduced due to the influence of the shielding structure 61, since the base point of the formed capacitor rises as a function of the charge in the readout node 41 and the resulting voltage signal at the signal output 44 of the conversion transistor 43.

[0166] Figures 5 to 10 To correspond Figure 2 1 shows an alternative embodiment of an image sensor having pixels 11 .

[0167] according to Figure 5In the exemplary embodiment, shielding structure 61 is only indirectly connected to signal output 44 of transfer transistor 43, namely via an assigned readout conductor or column conductor 17 and impedance converter 162. For this purpose, column conductor 17 is connected to the positive input of impedance converter 162. Since this input has a high resistance, it does not influence the output signal of the assigned transfer transistor 43 of pixel 11 of the corresponding column, which is conducted via column conductor 17. The output of impedance converter 162 is connected to shielding structure 61 of the corresponding pixel 11 via connecting conductor 163. Thus, a common impedance converter 162 is provided for a plurality of pixels 11 (particularly outside the pixel area of ​​the image sensor), wherein coupling between signal output 44 of transfer transistor 43 and shielding structure 61 of the corresponding pixel 11 can be selectively established via selection switch 47 of the corresponding pixel 11.

[0168] Impedance converter 162 can prevent the capacitance of the readout conductor or column conductor 17 from being accidentally increased by the corresponding shielding structure 61 of the assigned pixel 11 when such an arrangement is used, and prevent the voltage signal transmitted via column conductor 17 from affecting the switching transistor 43. Thus, impedance converter 162 forms decoupling circuit 160.

[0169] Relative to Figure 5 , according to Figure 6 In the embodiment of FIG. 1 , a corresponding coupling switch 147 is additionally provided in the connecting wire 163 between the output end of the impedance converter 162 and the shielding structure 61 of the corresponding pixel 11. The shielding structure 61 is selectively coupled or decoupled (directly, i.e., through the impedance converter 162) to the signal output end 44 of the conversion transistor 43 via the coupling switch 147. This allows the output end of the impedance converter 162 to be selectively coupled to the corresponding shielding structure 61 only at specific times. Thus, for example, it is possible to prevent the potential of the corresponding shielding structure 61 from being altered by the shielding structure 61 of another pixel 11 connected thereto.

[0170] The coupling switch 147 divides the connecting line between the output terminal of the impedance converter 162 and the shielding structure 61 of the corresponding pixel 11 into a first portion 163 and a second portion 63 ′.

[0171] exist Figure 6 In the embodiment shown in FIG, the coupling switch 147 is controllable together with the select switch 47 of the corresponding pixel 11. This can be achieved in a particularly simple manner by using a shared control line SEL. This ensures that when the voltage signal of the corresponding pixel 11 is actually to be read out, the corresponding shielding structure 61 is only connected to the output of the impedance converter 162 and is set to a potential corresponding to the voltage signal of the converter transistor 43.

[0172] If a coupling switch 147 (e.g. Figure 6 As shown, it can be controlled together with the selection switch 47 of the corresponding pixel 11, or can be controlled individually), so that in principle even the coupling circuit 160 or the impedance converter 162 can be omitted, that is, the shielding structure 61 of the corresponding pixel 11 can be coupled to the signal output terminal 44 of the conversion transistor 43 via the coupling switch 147 of the corresponding pixel, the assigned readout line or column line 17, and the selection switch 47.

[0173] Figure 7 Examples and Figure 6 The embodiment differs in that the impedance converter 162 is configured as an amplifier. For example, two capacitors 167 and 168 are shown in the feedback loop to adjust the amplification factor, although a voltage divider to ground potential 165, for example using an ohmic resistor, is also conceivable as an alternative. Feedback capacitor 167 can be bridged by means of switch 166 to deactivate amplification.

[0174] By configuring impedance converter 162 as an amplifier, the correlation between the potential of shield structure 61 and the voltage signal of conversion transistor 43 or the charge amount in readout node 41 can be increased. Impedance converter 162 can be designed to amplify the voltage signal of corresponding conversion transistor 43 with attenuated amplification characteristics.

[0175] Figure 8 Examples and Figure 6 The embodiment of the present invention differs in that the shielding structure 61 of the corresponding pixel 11 is couplable to a reference potential (particularly ground potential) via an additional coupling switch 171. Thus, the shielding structure 61 can be at a predetermined fixed potential when the additional coupling switch 171 is closed, thereby preventing unintended effects on the pixel 11 and, in particular, the readout node 41, due to an unspecified potential.

[0176] The additional coupling switch 171 can be controlled by the image sensor control device 153 via the control line FIX. The control device 153 can be designed to close only the selection switch 47 (for reading out the pixel 11) or only the additional coupling switch 171 (for keeping the potential of the shielding structure 61 unchanged) at a given time.

[0177] according to Figure 9 The embodiment corresponds to Figure 8 In an embodiment, the shielding structure 61 of the corresponding pixel 11 can be coupled to the power supply voltage VDD of the image sensor through an additional coupling switch 171.

[0178] Figure 10It is shown that the corresponding pixel 11 may include an additional shielding structure 61' in addition to the shielding structure 61, wherein both shielding structures 61, 61' partially surround the readout node 41. The two shielding structures 61, 61' may, for example, be U-shaped with opposing open sides to form a generally slotted ring shape with an isolation distance 66.

[0179] The two shielding structures 61, 61' can be at a potential related to the voltage signal at the signal output 44 of the switching transistor 43, but in a different manner. To this end, the shielding structure 61 can be as follows Figure 2 The embodiment of the present invention is directly connected to the signal output terminal 44 of the conversion transistor 43 of the corresponding pixel 11 through the connecting wire 63. Another shielding structure 61' can be as follows Figure 7 The embodiment is coupleable via a coupling switch 147 to the output of an impedance converter 162, which is a component of a decoupling circuit 160 and whose input is coupleable via a readout conductor or column conductor 17 and a corresponding selection switch 47 to the signal output 44 of the conversion transistor 43.

[0180] Described and Figures 2 to 10 Related embodiments may also be combined in other ways.

[0181] The following will be based on Figure 11 and Figure 12 , a preferred embodiment of a pixel 11 with a shielding structure 61 having a compact architecture is described.

[0182] Figure 11 A top view of the components of pixel 11 is shown, arranged in a first plane and a lower plane. Photosensitive element 15a of pixel 11 is shown, while a portion of photosensitive element 15b adjacent to the pixel can be seen. This is a backside illuminated (BSI) image sensor, meaning that exposure is from below relative to the viewing direction. Photosensitive elements 15a and 15b are octagonal and are arranged so that they are adjacent to each other on a total of four sides. This results in a high fill factor in the illustrated plane.

[0183] The other components of the corresponding pixel 11 are arranged between the remaining four (oblique) sides. The transfer gate 39 can be seen and has a passage channel 239, which is covered by a gate contact 240 (indicated by light hatching) and is connected to a contact for the control conductor TRF. Further, a part of the readout node 41 (floating diffusion (FD)) can be seen. Further, the transfer transistor 43 can be seen. The transfer transistor 43 includes: a drain contact, which is connected to the power supply voltage 51 at VDD; a passage channel 243; and a source contact, which forms the signal output terminal 44. The gate contact 244 of the transfer transistor 43 is indicated by light hatching. These "connectors" of the pixel 11 should generally be understood as functional elements and can be formed by corresponding regions of the pixel 11 (for example, in the semiconductor substrate) and / or by the delimiting structure of the pixel 11.

[0184] The readout node 41 (Floating Diffusion (FD)) extends to the top side of the gate connection 244 of the transfer transistor 43, which will be explained further below. The signal output 44 of the transfer transistor 43 is connected to the selection switch 47 via the output conductor 144. Therefore, the signal output 44 of the transfer transistor 43 can be selectively connected to the connection for the column conductor 17 via the selection switch 47. To this end, the gate connection 247 of the selection switch 47 (indicated by light hatching) includes a connection for the control conductor SEL. Further, the reset switch 45 can be seen, which selectively connects the connection VDD for the power supply voltage 51 (here indirectly via the additional transfer gate 73 mentioned below) to the readout node 41. The reset switch 45 includes a gate connection 245 (indicated by light hatching), which is connected to the control conductor RES. Further, the connection for the ground conductor GND can be seen.

[0185] Optionally, as combined Figure 4 As described, the pixel 11 may have an overflow capacitor 71 (at Figure 11 and Figure 12 ), the overflow capacitor 71 can be selectively connected to the readout node 41 via an additional transfer gate 73, wherein the additional transfer gate 73 has a gate contact 273 (indicated by a bright hatched line) having a contact for the control wire TG2.

[0186] Pixel 11 in Figure 11The components shown in FIG and described above are arranged substantially in a common plane. The electrical connections shown (in particular the access channel 239 of the transfer gate 39 and the access channel 243 of the conversion transistor) can be formed by doping the semiconductor substrate used (for example, silicon) (for example, by diffusion or implantation). The so-called gate contacts 240, 244, 245, 247 and 273 can include aluminum or doped polysilicon. The gate contacts 240, 244, 245, 247 and 273 are relatively thin relative to the doped regions of the semiconductor substrate and can therefore be allocated to Figure 11 The first (lower) layout plane in.

[0187] Figure 12 The additional elements of pixel 11 are shown corresponding to Figure 11 In a top view of the second plane, these elements are arranged as metallizations. Figure 11 The first plane is above the first plane and extends in a vertical direction parallel to and offset from the first plane. Figure 11 The elements of the first plane in the image are still visible below the metallization. The metallization (eg aluminum or an aluminum alloy) can be produced, for example, by vapor deposition or sputtering and subsequently removed by etching. Figure 12 The metallization can be Figure 11 The semiconductor substrate, the electrical insulator and the metallization can form a sequence of layers which are successively materially bonded to one another.

[0188] Figure 12 The metallization shown in FIG. 3 (shown in dark hatching) forms electrical contacts, connections, and capacitors. Visible are contact areas 340 for gate contact 240 of transfer gate 39; contact areas 347 for gate contact 247 of select switch 47; contact areas 317 for column conductor 17; contact areas 345 for gate contact 245 of reset switch 45; and contact areas 371 (in FIG. 317 ) for connecting overflow capacitor 71. Figure 11 and Figure 12 73 for the additional transfer gate contact 273 of the contact region 373; will be used for Figure 11 A contact line 351 for connecting the two terminals VDD of the supply voltage 51 to each other; and a contact area 352 for the ground conductor GND. Figure 12 The metallization can be Figure 11 The related components in the circuit are electrically connected through vertical through-holes, i.e. through holes perpendicular to the Figure 11 The first, lower plane and Figure 12 In the second, upper plane, a metal strip extends through an electrical insulator (e.g., silicon dioxide).

[0189] Figure 11 and Figure 12 The readout node 41 of the pixel 11 in FIG. 1 includes a bridge 341 that connects the output of the transfer gate 39 to the gate contact 244 of the transfer transistor (43). The bridge 341 is a metal strip at Figure 12 The bridge portion 341 extends across the second, upper plane of the pixel 11 and crosses the signal output terminal 44 and the output conductor 144 of the transfer transistor 43. A first end of the bridge portion 341 is electrically connected to the output terminal of the transfer gate 39 via a first metal via extending also perpendicularly to the first and second planes of the pixel 11; and a second end of the bridge portion is electrically connected to the gate contact 244 of the transfer transistor 43 via a second metal via extending also perpendicularly to the first and second planes of the pixel 11 (see Figure 12 Mark FD in).

[0190] Figure 11 and Figure 12 The shielding structure 61 of the pixel 11 includes a shielding portion 361. Figure 12 1 and 12. The shielding structure 61 extends in a circumferentially closed manner around the bridge portion 341 of the readout node 41, the bridge portion 341 extending in the same plane as the bridge portion 341. The shielding structure 361 partially covers the output terminal of the transfer gate 39, the signal output terminal 44 of the conversion transistor 43, and the output conductor 144. The shielding structure 361 is formed of a metal strip and is electrically connected to the signal output terminal 44 of the conversion transistor 43 or to the output conductor 144 via a third metal through-hole that also extends perpendicularly to the first and second planes of the pixel 11, and the output conductor 144 connects the signal output terminal 44 to the selection switch 47. Therefore, the third metal through-hole forms the already mentioned connecting conductor 63, which connects a part of the shielding structure 61 (i.e., the shielding structure 361) to the signal output terminal 44 of the conversion transistor 43 or to the output conductor 144, and is in the vertical direction. Since the first and second planes of the pixel 11 extend at a small distance from one another (approximately in the order of magnitude of the horizontal extension of the pixel 11 ), the (vertical) connecting line 63 is relatively short in this exemplary embodiment.

[0191] The shielding structure 61 and in particular the shielding portion 361 are thereby set to a potential that is dependent on the voltage signal of the switching transistor 43. Referring to the shortest path that can be shown from the output of the transfer gate 39 to the gate terminal 244 of the converter transistor 43 (see Figure 12 ), the annular shield 361 surrounds more than half of the section, ie the entire bridge portion 341 extending in the second, upper plane.

[0192] By means of the components of pixel 11 Figure 11 and Figure 12 The arrangement shown in FIG can achieve a smaller expansion of the readout node 41, with a smaller capacitance. The transfer gate 39 and the conversion transistor 43 can be arranged in a common plane ( Figure 11 ). Since bridge portion 341 of sense node 41, and thus the main portion of sense node 41, is completely surrounded on the sides by annular shielding portion 361 and is set to the potential at signal output 44 of switching transistor 43, the effective capacitance of sense node 41 is reduced. A further reduction in the effective capacitance of sense node 41 is achieved by bridge portion 341 of sense node 41 crossing signal output 44 of switching transistor 43 and output conductor 144, and by signal output 44 of switching transistor 43 and output conductor 144 connected thereto acting as an additional portion of shielding structure 61, which partially surrounds bridge portion 341 of sense node 41 on the lower side of sense node 41.

[0193] A further reduction in the effective capacitance of the readout node 41 can be achieved by: the shield structure 61 comprises an additional shielding portion 261, which is located at Figure 11 The additional shielding portion 261 extends in the first, lower plane of the pixel 1 near the switching transistor 43. The additional shielding portion 261 can be formed by doping the semiconductor substrate used, similarly to the signal output terminal 44 and the output conductor 144 of the switching transistor 43. The additional shielding portion 261 is formed in the shape of a corresponding finger, which extends straight or curved from the signal output terminal 44 of the switching transistor 43 with its free end.

[0194] exist Figure 11 In the embodiment shown, the corresponding additional shielding portion 261 is parallel to and close to the pass channel 243 of the switching transistor 43 (see FIG. Figure 11 ). Thus, the two additional shielding portions 261 together with the signal output 44 of the switching transistor 43 form a C-shape, which surrounds the switching transistor 43 on three sides and in particular its access channel 243 and its gate connection 244. Furthermore, the respective additional shielding portions 261 are offset parallel to and extend in the same direction relative to the annular shielding portion 361 located in the second plane of the pixel 11 (see Figure 12 The additional shielding portion 261 can also protrude in the direction of the transfer gate 39 (in the direction of the transfer gate 39) as a finger-shaped extension of the signal output terminal 44 of the switching transistor 43, for example. Figure 11 not shown).

[0195] The combination of these measures (annular shield 361 in the second, upper plane of the pixel 11 and one or more additional shields 261 in the first, lower plane) achieves a significant reduction in the effective capacitance of the readout node 41 .

Claims

1. An image sensor for an electronic camera, comprising a plurality of pixels (11) for generating exposure-related signals, wherein each of said pixels (11) comprises at least: - a photosensitive element (15) to generate an electric charge from incident light, - readout node (41), - a transfer gate (39) to selectively couple the photosensitive element to the readout node (41), - a conversion transistor (43) for converting the charge present at said readout node (41) into a voltage signal at a signal output (44), and a selection switch (47) connected to the signal output (44) of the switching transistor (43) for selectively coupling the signal output (44) of the switching transistor (43) to an assigned readout conductor (17) of the image sensor; Each pixel (11) has an electrically conductive shielding structure (61), the shielding structure (61) at least partially surrounding the readout node (41) and capable of being set to a potential related to the voltage signal at the signal output terminal (44) of the conversion transistor (43), The readout node (41) includes a bridge portion (341) connecting the output end of the transfer gate (39) to the gate terminal (244) of the conversion transistor (43). wherein the transfer gate (39) and the conversion transistor (43) are located in a first plane of the pixel (11), and the bridge portion (341) is located in a second plane of the pixel (11), the second plane being offset parallel to the first plane, The shielding structure (61) includes a shielding portion (361), the shielding portion (361) is located in the second plane of the pixel (11) and at least partially surrounds the bridging portion (341).

2. The image sensor according to claim 1, in, The shielding structure (61) can be connected directly or indirectly to the signal output (44) of the switching transistor (43).

3. The image sensor according to claim 1, in, The selection switch (47) is connected to the signal output end (44) of the conversion transistor (43) of the pixel (11) via an output conductor (144), wherein the shielding structure (61) is connected to the signal output end (44) of the conversion transistor (43) via the output conductor (144).

4. The image sensor according to claim 1, in, The shielding structure (61) can be coupled to the signal output (44) of the switching transistor (43) via the assigned readout line (17) of the image sensor and the selection switch (47).

5. The image sensor according to claim 4, in, The shielding structure (61) can be connected to the assigned readout line (17) of the image sensor via an impedance transformer (162).

6. The image sensor according to claim 5, in, The impedance converter (162) is configured to amplify the voltage signal of the conversion transistor (43).

7. The image sensor according to claim 6, in, The impedance converter (162) is configured to amplify the voltage signal of the conversion transistor (43) using switchable amplification and / or attenuation amplification characteristics.

8. The image sensor according to claim 1, in, The shielding structure (61) can be coupled directly or indirectly to the signal output terminal (44) of the switching transistor (43) via a coupling switch (147).

9. The image sensor according to claim 8, in, The coupling switch (147) and the selection switch (47) of the pixel are controllable together.

10. The image sensor according to claim 1, in, The shielding structure (61) can be coupled to a reference potential via an additional coupling switch (171).

11. The image sensor according to claim 1, in, The shielding structure (61) surrounds the readout node (41) on at least three sides.

12. The image sensor according to claim 1, in, The shielding structure (61) is circumferentially closed, and / or Wherein, the shielding structure (61) has an O shape.

13. The image sensor according to claim 1, in, The shielding structure (61) is circumferentially open, and / or Wherein, the shielding structure (61) has a C shape or a U shape.

14. The image sensor according to claim 1, in, The shielding structure (61) extends in a plane, The shielding structure (61) can be directly or indirectly connected to the signal output end (44) of the conversion transistor (43) via a connecting wire (63), wherein at least a portion of the connecting wire (63) adjacent to the shielding structure extends approximately perpendicular to the extension plane of the shielding structure (61).

15. The image sensor according to claim 1, in, The bridge portion (341) is connected to the output end of the transfer gate (39) via a first through hole extending perpendicularly to the first plane of the pixel (11), wherein the bridge portion (341) is connected to the gate contact (244) of the conversion transistor (43) via a second through hole extending perpendicularly to the first plane of the pixel (11).

16. The image sensor according to claim 1, in, The bridge portion (341) crosses the signal output terminal (44) of the conversion transistor (43).

17. The image sensor according to claim 1, in, The access channel (239) of the transfer gate (39) and the access channel (243) of the conversion transistor (43) are formed by conductive channels of a semiconductor substrate, wherein the bridge portion (341) is formed by a metal strip on the semiconductor substrate.

18. The image sensor according to claim 17, in, The image sensor is designed as a back-illuminated image sensor, wherein the first plane of the pixel (11) is formed by the semiconductor substrate and the second plane of the pixel (11) is formed by the metal strip, wherein the first plane of the pixel (11) and the second plane of the pixel (11) are separated from each other by an electrical insulator layer.

19. The image sensor according to claim 1, in, The shielding portion (361) forms a circumferentially closed ring, which surrounds the bridge portion (341) in the second plane of the pixel (11).

20. The image sensor according to claim 1, in, The shielding portion (361) at least partially covers the output terminal of the transfer gate (39) and the signal output terminal (44) of the conversion transistor (43).

21. The image sensor according to claim 1, in, The shielding portion (361) is connected to the signal output terminal (44) of the conversion transistor (43) through a third through hole extending perpendicularly to the first plane of the pixel (11).

22. The image sensor according to claim 1, in, The shielding structure (61) includes an additional shielding portion (261), the additional shielding portion (261) is located in the first plane of the pixel (11), and the additional shielding portion (261) is arranged close to the transfer gate (39) and / or close to the conversion transistor (43).

23. The image sensor according to claim 22, in, The additional shielding portion (261) is formed into a long finger shape with a free end.

24. The image sensor according to claim 22, in, The additional shielding portion (261) extends parallel to the access channel (243) of the switching transistor (43), and / or wherein, The additional shielding portion (261) is offset in parallel and extends in the same direction relative to a portion of the shielding portion (361) located in the second plane of the pixel (11).

25. The image sensor according to claim 1, in, The shielding structure (61) surrounds more than half of the shortest path extending from the output terminal of the transfer gate (39) to the input terminal of the conversion transistor (43).

26. The image sensor according to claim 1, The pixel (11) further comprises: - a reset switch (45) for selectively coupling the readout node (41) to a reset potential (51); - an overflow capacitor (71) and an additional transfer gate (73) to selectively couple the readout node (41) to the overflow capacitor (71).

Images