Optical isolation system and circuit, and photon detector with extended lateral pn junction

Abstract

To provide an optical isolation system with a high current transfer ratio that can be used in low noise, high efficiency power supply application, as well as optically isolated data transmission or photon detector application, and a photon detector with extended lateral p-n junction.SOLUTION: An optical isolation system includes a lateral photovoltaic sensor including one or more P-type semiconductor structures 101 and N-type semiconductor structures 103 and an LED light source 108, and each of the P-type semiconductor structure 101 and the N-type semiconductor structure 103 includes a lateral sensor surface 107b for receiving photons of a given wavelength λ, and an extended lateral junction region with an effective junction distance D greater than five times the absorption depth for the semiconductor structure corresponding to the given wavelength λ.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] Isolation circuits involve data and / or power transmission across a galvanic isolation barrier to interconnect electrical systems powered by different sources that do not share a common ground connection. Transformer isolation approaches involve switching circuits and magnetic fields, and the resulting electromagnetic interference (EMI) can be undesirable in some applications. Transformer isolation also typically requires additional transformer components, and these solutions require large circuit area and are costly. While capacitive or AC coupling can be used to provide isolation for data transmission, capacitor-based isolation solutions can involve parasitic capacitance that absorbs signal energy and reduces power efficiency. High-voltage breakdown voltage ratings also require thick layers of surface dielectric, making them costly to implement using capacitive coupling. Optical isolation avoids the EMI and circuit area issues associated with transformer isolation by transmitting power / electrical signals between galvanically isolated circuits using light through a photon emitter (e.g., a light-emitting diode or LED), a receiver or sensor such as a photovoltaic diode (PVD), and an optical coupling material. Optical coupling devices, or optocouplers, typically stack an LED light source on top of a PV diode with glass or other transparent material between them to transmit photon energy vertically downward to the top of the PVD sensor. Also, high breakdown voltage isolation ratings can only be achieved by increasing the distance between the LED and the PVD, which can result in unacceptable vertical device height. Some high-isolation-voltage optocouplers use a reflective dome to reflect light from the LED onto the photodiode, arranged side-by-side for upward transmission by the LED and downward reception by the photodiode. In these traditional optocoupler approaches, the photon path is perpendicular to the surface of the silicon device. LED light sources typically provide optical signals at or near infrared wavelengths, and optocouplers generally exhibit poor power efficiency (e.g., current transfer ratio or CTR, which represents the ratio of input current to output current). Common-mode transient isolation (CMTI) is also an issue in vertical configurations due to capacitive coupling between the emitter and detector. Thus, conventional optical isolation techniques do not provide an adequate solution for many power transfer applications. Summary of the Invention

[0002] Disclosed examples include lateral photovoltaic sensors and systems, as well as optical isolation circuits comprising semiconductor structures including a lateral sensor surface for receiving photons of a given wavelength and an extended lateral junction region having an effective junction distance exceeding the absorption depth for the semiconductor material corresponding to the given wavelength, facilitating high efficiency for data and / or power transmission across a galvanic isolation barrier. In certain examples, the laterally extended p-n junction is formed by multiple n-doped regions diffused or implanted into a p-doped region to form a series of p-n junctions spaced across the effective lateral junction distance. The extended single or split p-n junction provides a significantly higher photon capture probability compared to vertical photodiode structures, facilitating high efficiency and current transfer ratios in various applications. Further disclosed examples for optical isolation of high-speed signal information include optical sensor circuits for detecting optical signals of a given wavelength along a lateral optical path using a laterally extended p-n junction array with a bias quenching circuit for biasing the junction near avalanche. In this application, the capture of a single photon causes the pn junction to conduct an avalanche of current, resulting in direct amplification. [Brief explanation of the drawings]

[0003] [Figure 1] FIG. 1 is a cross-sectional side view of an optically isolated integrated circuit including an LED light source and a lateral light-receiving diode sensor comprising a semiconductor structure having multiple pn junctions spaced laterally over an extended effective junction distance in an internal cavity of a molded package structure that provides an optical path for electrical isolation, according to one embodiment.

[0004] [Figure 2] 10 is a cross-sectional side view of another optically isolated IC embodiment comprising an LED light source and a lateral photodiode sensor including a reflective coating formed on a concave surface of a package cavity.

[0005] [Figure 3] FIG. 10 is a cross-sectional side view of another optically isolated IC embodiment having a glass or plastic optical transmission medium positioned between an LED light source and a lateral photodiode sensor.

[0006] [Figure 4] FIG. 10 is a cross-sectional side view of another optically isolated IC embodiment with a photosensor including two vertically stacked lateral photodiode semiconductor structures, each including multiple pn junctions, to form a lateral multi-stage photovoltaic (LMSPV) photosensor.

[0007] [Figure 5] 5 is a partial cross-sectional side view of light reception in the optical sensor of FIG. 4.

[0008] [Figure 6] FIG. 10 is a cross-sectional side view of another optically isolated IC embodiment with a photosensor including four vertically stacked lateral photodiode semiconductor structures each including a single extended pn junction.

[0009] [Figure 7] 7 is a partial cross-sectional side view of light reception in the optical sensor of FIG. 6.

[0010] [Figure 8] 1 is a cross-sectional side view of another exemplary isolation circuit including an infrared or near-infrared light source with a parabolic focusing mirror and a photodiode semiconductor structure including a single extended pn junction.

[0011] [Figure 9] 1 is a partial schematic diagram of an optical isolation system, including a plan view of an example of a laterally extended junction photodiode semiconductor structure with an exemplary output current tap;

[0012] [Figure 10] 10 is a graph of collected tap current as a function of effective junction distance in the semiconductor structure of FIG. 9.

[0013] [Figure 11] 1 is a graph of an example absorption depth curve as a function of photon wavelength for silicon.

[0014] [Figure 12] FIG. 1 is a simplified schematic diagram of an example isolated low dropout (LDO) regulator including an LMSPV pv bias generator array.

[0015] [Figure 13] FIG. 1 is a simplified schematic diagram of an example solid-state relay (SSR) including an LMSPV pv bias generator array.

[0016] [Figure 14] FIG. 1 is a simplified schematic diagram of an example isolated latching SSR including an LMSPV light sensor.

[0017] [Figure 15] FIG. 1 is a partial schematic diagram of a cross-sectional side view of an elongated isolated circuit including a light source and an LMSPV light sensor connected by an optical fiber. [Figure 16] FIG. 1 is a partial schematic diagram of a cross-sectional plan view of an elongated isolated circuit including a light source and an LMSPV light sensor connected by an optical fiber.

[0018] [Figure 17] FIG. 1 is a partial schematic diagram of a top cross-sectional view of an optically isolated system including a light source IC and an LMSPV light sensor coupled by an optical fiber.

[0019] [Figure 18] 18 is a partial schematic diagram of a plan view of an example LDO regulator including an LMSPV light sensor with a black polymer light barrier formed between the LMSPV light sensor and other circuit elements that may be used in the system of FIG. 17.

[0020] [Figure 19]FIG. 1 is a partial schematic diagram of a plan view of an example LDO regulator with multiple LMSPV photosensor channels separated by black polymer barriers.

[0021] [Figure 20] FIG. 1 is a partial schematic diagram of a plan view of an example LDO regulator comprising multiple LMSPV photosensor channels separated by black polymer barriers, each including a curved trench filled with a reflective material around the LMSPV photosensor channel.

[0022] [Figure 21] FIG. 1 is a partial schematic diagram of a plan view of an example LMSPV photosensor semiconductor structure showing further details of some example interconnected semiconductor structures that individually include multiple n-doped regions in a p-doped region to form multiple laterally spaced p-n junctions.

[0023] [Figure 22] FIG. 1 is a partial schematic diagram of an exemplary photon sensor including a lateral photosensor semiconductor structure with multiple pn junctions arranged along an extended effective junction distance and a quenching circuit to provide a photon multiplication circuit.

[0024] [Figure 23] FIG. 10 is a partial schematic diagram of another exemplary photon sensor including a lateral photosensor semiconductor structure with a single pn junction disposed along an extended effective junction distance and a quenching circuit to provide a photon multiplication circuit. DETAILED DESCRIPTION OF THE INVENTION

[0025] In the figures, like reference numerals refer to like elements throughout, and various features are not necessarily drawn to scale. In the following description and claims, the terms "including," "having," and "comprising," or variations thereof, like the term "comprising," are inclusive and therefore should be interpreted to mean "including, but not limited to." Also, the term "couple" includes an indirect or direct electrical or mechanical connection, or a combination thereof. For example, if a first device is coupled to a second device, the connection may be through a direct electrical connection, or may be indirectly connected through one or more intervening devices and connections.

[0026] Referring first to FIG. 1 , lateral photovoltaic sensors and systems are disclosed that include one or more semiconductor structures including a lateral sensor surface for receiving photons from a light source. The semiconductor structure includes an extended lateral junction region with an effective junction distance greater than the absorption depth for the semiconductor material corresponding to the wavelength of the received optical signal. Various embodiments provide optical isolation devices and systems that include a light source and a lateral optical sensor with a separation distance between the light source and the optical receiver to establish a high breakdown or isolation voltage rating for the device. The extended effective junction distance also facilitates a high current transfer ratio between the light source current and the current generated by the optical sensor, providing a solution for more efficient power transfer across the galvanic isolation barrier. Various examples include sensor circuits with optical boundaries around the sensor channel to reduce crosstalk and enable internal reflection for efficient transfer of power and / or data signals between the light source and the sensor. Multi-channel data transmission implementations are possible, along with single- or multi-channel power transfer embodiments. The disclosed examples may also be used for photon sensors such as photon multipliers and other detection circuits. In various examples, the extended lateral length of the p-n junction promotes a high photon capture probability for achieving high efficiency. Some examples include a single extended p-n junction in the semiconductor structure. Other examples provide multiple p-n junctions laterally disposed across the extended effective junction distance. Also, in some examples, multiple extended junction semiconductor structures are interconnected to form a lateral multi-stage photovoltaic (LMSPV) photosensor to provide a variety of different output currents and / or voltages for power transfer applications. LMSPV structures may also be used for data transfer applications. The disclosed examples advantageously promote the use of optical isolation to avoid or mitigate the aforementioned drawbacks of magnetic and capacitive isolation techniques for power and / or data transfer, while promoting higher efficiencies than were possible with previous optocouplers and optical isolation devices. In some embodiments, bias or quench circuitry is combined with the extended junction semiconductor structure to form a photon detector with integrated amplification, commonly referred to as a silicon photon multiplier (SiPM) device.

[0027] FIG. 1 shows an optically-isolated integrated circuit (IC) 100 including a molded structure 102 with one or more conductor structures 104 to form an integrated circuit package containing an LED light source 108 and a lateral photosensor 106. An optical signal travels from a lateral signal output face 107a of the light source 108 through a cavity 110 of the integrated circuit package structure 102 along an optical path 114 to a lateral sensor face 107b of the photosensor 106. In one example, the light source 108 is an LED fabricated in a first GaAs semiconductor die or other circuit structure 105, although in other embodiments, a laser, silicon-based photon emitter, or other light source may be used. The sensor 106 includes a semiconductor structure formed by a p-doped region 101 and one or more n-doped regions 103 to form multiple laterally spaced p-n junctions over an extended effective junction distance D. In the illustrated example, the optical sensor 106 is fabricated as a second device or circuit structure with a vertical front side forming a lateral sensor surface 107b facing the optical path 114 for receiving an optical signal. The optical sensor 106 provides one or more pn junctions along an extended effective junction distance D, shown schematically in FIG. 1 as diodes 111. The circuit structures 105 and 106 each include bond pads 122 connected to corresponding conductors 104a, 104b of a lead frame structure by bond wires 124. In one example, the conductors 104a, 104b are IC pins or pads that can be soldered to a host printed circuit board (PCB, not shown). In one example, an external circuit (not shown) provides an electrical signal to the light source 108 via the pair of input conductors 104a, which generates an optical signal along the optical path 114 in response to the received electrical signal. Also in this example, IC 100 includes bond pads 122 that are electrically connected by corresponding bond wires 124 to a second pair of lead frame conductors 104b, shown generally in Figure 1, for providing an electrical output signal from light sensor 106. Conductors 104b in the illustrated example provide pads or pins of IC 100 that can be soldered to a host PCB for carrying electrical signals from sensor 106 that are isolated from the light source signal in conductors 104a.The isolation voltage rating or breakdown voltage of the isolator IC 100 in this example is set by the separation or gap distance 116 that separates the circuit structures 105 and 106 across the galvanic isolation boundary.

[0028] The signal output surface 107a and the sensor surface 107b are generally in parallel planes and are spaced apart from each other in the cavity 110 by a distance 116. In other possible examples, these surfaces 107 need not be parallel. Any relative configuration can be used, with the sensor surface 107b at least partially facing the light source 108 to receive an optical signal. The sensor surface 107b directs light into the structure 106 to generate an output electrical signal corresponding to the intensity of the optical signal. The sensor circuit 106 may further include interface circuitry (not shown) to operate on the sensor signal. As shown in FIG. 1, a significant portion of the surfaces 107a and 107b are exposed within the cavity 110, although this is not a strict requirement for all possible embodiments. In the example of FIG. 1, the light source 108 and the light sensor 106 are spaced apart from each other in the internal cavity 110 of the molded package structure 102 to provide electrical isolation therebetween. The cavity 110 in this example provides a solid-free (e.g., solid-free) optical path 114. In other examples (e.g., FIGS. 3 and 4 below), glass or other optically transparent solid structures may be provided between the light source 108 and the light sensor 106. The cavity 110 in one example is sealed and contains air or other optically transparent gas, which may advantageously have a lower dielectric constant than glass or other transparent solid materials, thereby reducing capacitive coupling between the light source 108 and the sensor 106. In the example of FIG. 1, the cavity 110 includes a concave top surface 112, although this is not a strict requirement in all possible implementations. In one example, the cavity 110 may be formed during formation of the molded structure 102 using a deposited sacrificial sublimation material, followed by evaporation or sublimation through a port 118 to create the solid-free cavity 110. The port 118 may then be closed with tape or other closure structure 120 to form a hermetic seal for the cavity 110. In some examples, the insulating gap or separation 116 is controlled by a mechanical feature on one of the dies or circuit structures 105, 106, such as an oxide bump (not shown) extending between the die 105 and the die 106, which sets the gap distance 116.The gap 116, in some examples, is controlled by mixing a filler material of a specific size with the sacrificial material used to form the cavity 110. In the illustrated example, the interior surface of the package structure 102 includes a concave portion provided by forming the sacrificial material as one or more droplets during manufacturing, such as using a printing process. This deposited sacrificial material thus forms a partially convex structure that sublimes or evaporates after formation of the molded package structure material 102, leaving the concave interior surface intact. As shown in FIG. 1 by the diagonal line 113, the concave shape of the cavity interior surface can extend beyond the edges of the dies 105 and 106, allowing light to exit the top of the LED light source 105 and enter the top of the sensor die 106.

[0029] In one example, IC 100 is an optically isolated circuit for transmitting data or power from an electrical circuit connected to light source 108 to an electrical circuit (not shown) connected to sensor 106. Light source 108 generates an optical signal of a given wavelength λ along optical path 114. In one example, the light source is a lateral LED that provides a signal at a wavelength λ of approximately 950 nm. Any other suitable light source wavelength λ may be used. As used herein, an optical signal of a given wavelength λ refers to the specified wavelength, as well as other wavelengths that are close to the specified value, such as within a few percent of the specified value or any suitable wavelength tolerance associated with the LED or other light source used for the optical isolation device. In one example, light source 108 provides a long wavelength signal with energy just above the bandgap energy of silicon to maximize absorption depth in the semiconductor structures 101, 103 of optical sensor 106. Wavelengths λ with energy levels below the bandgap energy of silicon interact weakly with silicon, while λ with energy levels above or much above the bandgap energy of silicon are strongly absorbed, with the energy fraction above the bandgap being wasted as the electrons rapidly thermalize down. In some instances, lateral devices are optimal for wavelengths at the bandgap energy where the silicon length can be increased to obtain maximum trapping.

[0030] The optical sensor 106 is designed for operation in receiving and capturing laterally received photons of a given wavelength λ. The optical sensor 106 in the example of FIG. 1 includes a semiconductor structure having a top T and a bottom B, and a front side at least partially facing the optical path 114 to provide a sensor surface 107b for receiving an optical signal from the light source 108. The semiconductor structure further includes a back side spaced apart from the front side, and side surfaces extending vertically between the top T and the bottom B and horizontally between the front and back sides. In the illustrated example, the semiconductor structure is generally rectangular with generally parallel front and back sides, and the top and bottom are generally planar and parallel to one another. The illustrated example also provides generally planar side surfaces. However, other semiconductor structure shapes may be used. Any suitable semiconductor structure may be used. In certain examples, the semiconductor structure is silicon (Si). In other examples, gallium arsenide (GaAs) or other suitable semiconductor materials may be used.

[0031] The semiconductor structure includes a p-doped portion 101 having boron or other p-type dopant. In some implementations, the p-doped portion 101 extends along at least a portion of the bottom portion B, as shown in FIG. 1 . In one example, fabrication of the semiconductor structure begins with a p-doped silicon substrate from which portion 101 is formed. The p-type portion exits the bottom portion B and is electrically connected to the package electrical connector 104b. In another example, to form the p-doped portion 101, p-type dopants are introduced into the semiconductor substrate by implantation and / or diffusion. The semiconductor structure also includes one or more n-doped portions 103 comprising phosphorus or other n-type dopants at least partially adjacent to the p-doped portion 101. The n-doped portions exit the top portion T and are electrically connected to electrical connections 122 and 124 to another package electrical connector (not shown). The n-doped portion or portions 103 form at least one p-n junction within the semiconductor structure. The resulting p-n junction or junctions extend between the front and back sides of the semiconductor structure an effective junction distance D. In some examples, the effective junction distance D is greater than a constant K times the absorption depth of the semiconductor structure for a given wavelength λ, where K is greater than 1.

[0032] As used herein, the absorption depth for the semiconductor structures 101, 103 is the distance value (e.g., in FIG. 1 , extending from the sensor face 107b to the right into the semiconductor structure) over which the incident radiation intensity is reduced by 1 / e, or approximately 36%. At this distance, the amount of photon energy absorbed by the silicon 101, 103 through the creation of electron-hole pairs may be approximately 64% of a given wavelength λ received at the lateral sensor face 107b. In one example, K is 5 or greater. In another example, K is 10 or greater. In a further implementation, K is 20 or greater. The junction distance D may be any suitable size within the practical physical limits of a given end-use application, such as, for example, K being less than 1000. The n-doped portion in one example extends along at least a portion of the top T, although this is not a requirement for all possible implementations. The extended effective pn junction distance promotes a high rate of absorption of incident photons received at the lateral sensor surface 107b. For example, as shown and described hereinafter in connection with FIGS. 9 and 10, photon capture and resulting carrier generation have a high probability at or near the entrance to the sensor surface 107b of the semiconductor structure, and the probability of photon capture decreases with increasing distance from the front side of the semiconductor structure. In the disclosed lateral devices, the lateral dimension is the plane (horizontal) distance of a standard thickness silicon wafer. In many manufacturing processes, silicon wafers are back-ground to a thickness of about 10 mm, and a standard vertical photovoltaic sensor can only have a path length of about 254 microns. Furthermore, only the top 20 microns or so of this path length are useful for photon capture. Long junctions can be created by creating a very thick, multi-junction piece of vertical silicon and placing the assembled die stack on its side. However, this is a highly non-standard and impractical approach compared to lateral device construction.

[0033] Including one or more n-doped portions 103 in a semiconductor structure that extend or are distributed across substantially all of the effective p-n junction distance D promotes a high-efficiency photon capture probability by increasing the absorption depth corresponding to a particular semiconductor material and corresponding D for a given wavelength λ. For example, a highly efficient LED light source 108 can be used to transmit photons at a wavelength λ of approximately 950 nm. Using a silicon semiconductor structure with appropriately doped p and n portions 101 and 103, approximately 64% of the received photon energy is absorbed in the first 80 μm of travel for a 950 nm light source. The inventors have realized that high absorption is achieved for K values ​​of 5 or greater, with further improvement achieved by using K values ​​of 10 or greater. Furthermore, nearly complete (e.g., approaching 100%) absorption is achieved for K values ​​of 20 or greater. In the example of FIG. 1, the effective p-n junction distance D is implemented by creating multiple p-n junctions via corresponding n-doped regions 103 implanted and / or diffused on top of the p-doped portions 101. 1 shows five such n-doped regions 103 to create p-n junctions across substantially all of the distance D, but multiple n-doped regions 103 may be used to create a correspondingly larger number of p-n junctions. While the illustrated n-doped regions 103 are substantially uniformly spaced between the front and back sides of the lateral semiconductor structure, uniform spacing is not a strict requirement for all possible implementations, and multiple spacings and feature sizes may be used in various embodiments.

[0034] The resulting structures 101, 103 provide multiple pn junctions along a substantially straight corridor to promote high collection probability. In various embodiments, multiple such semiconductor structures can be used (e.g., FIG. 4), and the corresponding optical corridors can be electrically isolated. Interconnect circuitry can be provided in the IC 100 to connect the resulting pn extended junction cells in any desired series and / or parallel configuration. Individual semiconductor structures can also include upper and lower (e.g., top and bottom) reflective materials or structures 109 to provide internal reflections to promote capture of the majority of received photon energy and to optically isolate each channel from adjacent optical circuits. The multi-channel concept can also be extended for use in power transfer and data transfer applications, where optical isolation of different channels helps minimize crosstalk for communications applications. Also, as shown in FIG. 1, an optically reflective material 109 can be provided on the backside of the semiconductor structures 101, 103 so that all photons encountered at the backside are reflected toward the sensor surface 107b, thereby further improving collection efficiency. Similarly, in some embodiments, light reflective material may be provided on the sides (not shown) of the semiconductor structures 101, 103 to further increase the probability of a given incident photon being collected by the sensor structure.

[0035] As described above, in certain examples, multiple semiconductor structures 101, 103 may be included, and these cells may be stacked or interconnected in any suitable series and / or parallel manner to achieve a desired output voltage and / or power. In some examples (e.g., FIGS. 6-8 and 23), a single extended pn junction is provided in each semiconductor structure 101, 103 to create a single pn junction with a junction distance D by using a single n-doped portion 103. In other examples (e.g., FIGS. 1-5 and 12-22), each semiconductor structure 101, 103 includes multiple n-doped portions 103 containing n-type dopants to create multiple pn junctions across substantially all of the effective junction distance D between the front side and back side. The resulting photosensor 106 may be used for data and / or power transfer in certain applications. The extended junction lateral sensor structure 106 can also be used in photon multiplier applications, such as in the photon detector systems further described below in connection with FIGS. 22 and 23. Unlike conventional optocouplers, the disclosed extended junction devices and systems facilitate a high current transfer ratio (CTR) in power supply applications, and therefore facilitate efficient biasing of circuits separated by a galvanic isolation barrier. Furthermore, the distance 114 in FIG. 1 can be sized according to any desired breakdown voltage or isolation voltage rating for a given application. Furthermore, this tunability of isolation level does not cause an increase in the vertical height of the IC 100, as would be the case with conventional vertically oriented optocouplers.

[0036] In operation of the photosensor 106, incident photons received laterally through the sensor surface 107b are absorbed at or near the extended p-n junction formed by the doped regions 101 and 103. In one form of operation, the sensor 106 and its corresponding extended p-n junction operate as a photodiode in a photovoltaic mode, generating carriers and corresponding current flow and producing an electrical output signal for use in power supply bias and / or data transmission. In particular, once a photon of sufficient energy is received, electron-hole pairs are created via the photoelectric effect internal to the semiconductor structures 101, 103. Upon absorption at or near the depletion region of the extended p-n junction, carriers follow the electric field of the depletion region and migrate away from the junction, with holes migrating toward the anode (p-doped region 101) and electrons migrating toward the cathode (one or more n-doped regions 103). This carrier movement generates a current flow that can be used to generate an electrical signal for associated circuitry connected to the sensor 106. For example, a low dropout (LDO) regulator or other power supply circuit may use the photo-generated current to power external circuitry connected to the sensor 106. In another example, the current flow generated by the sensor 106 may be used as a received data signal by external circuitry connected to the sensor. For example, in a silicon photon multiplier circuit, the generated signal from the sensor circuit 106 may be used to indicate the detection of an individual received photon, as described below in connection with Figures 22 and 23.

[0037] 2 illustrates another exemplary isolated IC embodiment 100 including an LED light source 108 and an extended junction lateral photosensor 106, as described above. In this example, the interior surface of the cavity 110 includes a reflective coating 200 that reflects light from the light source 108 toward the photosensor 106, for example, along an optical path 202. The reflective coating material 200 in one example is deposited on a convex sacrificial sublimation material prior to a molding process that creates the molded package structure material 102. Sublimation of the sacrificial material layer after the molding process leaves the cavity 110 defined at least in part by the concave surface of the residual reflective material layer 200. Any suitable non-conductive material 200 may be used that promotes reflection of all or a portion of the optical signal generated by the light source 108 toward the photosensor 106. 2, the optical signal from the light source 108 may travel along optical path 114, through the cavity 110, directly to the sensor face 107b of the sensor die 106, and / or the signal may also travel along a reflected path 202 via a reflective coating 200 on the concave surface 112. In another possible example, the concave surface 112 of the cavity 112 and any corresponding reflective coating 200 may be extended laterally to expose at least a portion of the top of the photosensor semiconductor structure, thereby allowing reflected photons to enter the top of the semiconductor structure for potential capture in the sensor 106.

[0038] 3 shows another non-limiting example isolated IC 100 including a light source 108 and a light sensor 106 as described above. In this example, an optically transparent structure 300 is disposed along the optical path 114 between faces 107a and 107b of the light source 108 and the light sensor 106. Any suitable material 300 may be used, such as glass, polymer, etc.

[0039] 4 and 5, FIG. 4 illustrates another optically isolated IC embodiment 100. In this example, the photosensor 106 includes multiple series-connected diodes, each of which includes p- and n-doped portions of a corresponding semiconductor structure 401, 402, as described above. The photosensor 111 in this example includes two series-connected photodiodes formed by two (e.g., bottom and top) substrates or dies 401 and 402, although any number of such stacked dies, two or more, may be used. In one example, the dies 401, 402 each include a top reflective coating material, for example, formed by an oxide layer 502 and a top passivation layer 504 on the top T of the corresponding semiconductor structure. A reflective silver-bearing epoxy is used on the bottom B of each of the semiconductor structures to form a bottom reflective surface for photon containment within the individual semiconductor structures and to bond the top semiconductor structure / die 402 to the bottom die 401. In this example, the photosensor structure 106 also includes a base die 400 comprising a semiconductor substrate containing any desired amplifiers, filters, or other interface circuitry (not shown), and a lower sensor die 401 is attached on top of the base die 400 using a light-reflective silver-loaded epoxy for attachment and photon reflection at the die 401. The dies 401 and 402, in one example, are background to have a smaller vertical height than the base die 400. In one example, the stacked dies 401 and 402 each include a metallization structure to provide an upward electrical connection to the n-doped portion 103, and the silver-loaded epoxy used to bond the dies 401 and 402 together may provide an electrical connection from the n-doped portion of the lower die 401 to the p-doped portion of the upper die 402 to effectively connect corresponding diodes in series with each other. In one example, individual dies 401 and 402 each generate a voltage signal of approximately 0.5 V, and stacked dies 401 and 402 may be interconnected in series to provide a higher output signal to external circuitry (e.g., 1.0 V). Embodiments having more than two stacked dies may be interconnected in any desired series and / or parallel configuration to achieve a desired output signal level in response to an optical signal from light source 108.

[0040] 6 and 7 show another example isolated IC 100 using multiple stacked diodes in a photosensor 106. The second circuit structure 106 in FIG. 6 is a multi-die structure with vertical diodes, each including a single p-doped portion and a single extended n-doped portion. Similar to the previous embodiment, this example provides an extended lateral p-n junction structure with an effective junction distance D longer than the absorption depth for the semiconductor structure corresponding to a given wavelength λ. The sensor structure in FIGS. 6 and 7 includes four stacked dies 601, 602, 603, and 604 formed on a base die 600, although any number of dies can be used. FIG. 7 shows some example light travel paths in the various dies 601-604.

[0041] 8-10, FIG. 8 illustrates an exemplary optical isolation circuit 800 including an LED light source 108 with a parabolic reflector-mirror structure 802. In one example, the light source 108 is an OSRAM SFH-4441 940 nm LED rated at 50 mW at 100 mA. An optical coupler structure 804 is provided between the LED / mirror component 108, 802, and the sensor surface 107b of a semiconductor structure including a single p-doped portion 101 and a single extended long n-doped portion 103, as described above. In this example, K is approximately 7. This example includes a reflective coating material 109, such as an oxide, on the top T of the semiconductor structure, as well as a reflective material 109 (e.g., a reflective epoxy) on the bottom B to promote photon reflection for increased capture probability, as shown in simplified form in FIG. 8. The semiconductor structures 101, 103 are attached to a pedestal 808 via epoxy 109, and the light source and sensor structures are attached to the base 806 in a spaced apart relationship to define a separation or gap distance 116 for setting the isolation level of the isolation circuit 800. In certain examples, electrical connections (not shown) are made to the n and p regions on the top side T.

[0042] Figure 9 shows a plan view of the semiconductor structure 101, 103 along line 9-9 in Figure 8. The structure includes one or more conductive taps 904 connected to corresponding areas of the n-doped portion 103 for collecting photo-generated current based on the capture of photons incident on the sensor surface 107b.

[0043] 10 provides a graph 1000 showing a curve 1002 of the tap current, in μ, at tap location 904 in FIG. 9 as a function of distance from the sensor surface 107b. As discussed above, the probability of photon capture, and therefore the magnitude of the photon-generated tap current, is highest at or near the sensor surface 107b and decreases with increasing distance in the semiconductor structure. In this example, approximately 64% of the total generated tap current is generated over an initial distance 902 from the sensor surface 107b, which corresponds to the absorption distance for a given semiconductor material and a given wavelength λ.

[0044] 11 shows a graph 1100 containing an example absorption depth curve 1102 as a function of wavelength λ (μm) for silicon semiconductor structures 101, 103. In this example, the depth for 64% absorption of incident photons at a photon wavelength of 940 nm is approximately 95 μm. Using this principle, a given optical sensor 106 can be designed with an effective junction distance D sufficient to achieve a desired collection efficiency target for a given light source wavelength λ and semiconductor material.

[0045] 12-21, a variety of different circuit structures and devices can be created using the extended junction photosensor 106. As mentioned above, some examples include a semiconductor structure comprising a p-doped portion and one or more n-doped portions to create a cell having a lateral sensor surface 107b and an extended effective junction distance D that is longer than the absorption depth of the corresponding semiconductor material for a given light source wavelength λ. The combination of multiple lateral cells interconnected in a series and / or parallel configuration is referred to herein as a multi-stage photovoltaic (LMSPV) sensor structure 106.

[0046] FIG. 12 illustrates an example isolated low-dropout (LDO) regulator device 1200 including a sensor structure implemented on an integrated circuit die or packaged multi-die device 1201. In this example, the sensor circuit 106 is formed as an LMSPV structure for receiving light from the lateral sensor surface 107b, as described above. The n- and p-doped portions of the LMSPV 106 are electrically connected to a switching circuit 1202 for electrically interconnecting the p-n junctions of the multiple semiconductor structures 101, 103 of the LMSPV 106. In one example, the switching circuit 1202 is programmable or otherwise configurable to allow changes to the series and / or parallel interconnections such that the device 1201 can provide an output signal (e.g., output voltage V in FIG. 12 ) having configurable voltage and current values. The electrical signal provided from the LMSPV 106 via the switching circuit 1202 is sent to an LDO regulator circuit 1204. The regulator circuit 1204 provides the output signal V to drive a load (not shown). Device 1200 advantageously provides a high current transfer ratio between a matched light source (not shown) and LMSPV light sensor 106 to implement a more efficient power supply with optical isolation across a galvanic isolation barrier.

[0047] 13 shows an isolated solid-state relay (SSR) device 1300 including an LMSPV 106 with a sensor surface 107b for receiving an optical signal that is pulsed on or off to selectively turn on power to a load. In one example, device 1300 is packaged in a single integrated circuit die or packaged multi-die structure 1301 including the LMSPV 106, series / parallel switching circuitry 1202 as described above, application-specific analog circuitry 1302 for implementing host swap functionality, and a power switch 1304. In one example, device 1300 can be used for an isolated power switch. Device 1300 advantageously facilitates providing on or off control signaling via LMSPV 106 from a signal source that is electrically isolated from the secondary side of the power delivery circuit.

[0048] 14 shows an isolated latching SSR device 1400 packaged in a single integrated circuit die or packaged multi-die structure 1401 with multiple LMSPV circuits 106 and corresponding lateral sensor faces 107b, as well as top and bottom hold-up capacitors 1402, gate drive circuitry 1404, and a DC or AC power switch 1304 for controlling the load. The device 1401 receives light from LED light sources 105, 108 at the sensor faces 107b, as described above. The hold-up capacitor 1402 provides latching of the output signal obtained from the LMSPV structure, activating the received light signal and latching the power switch 1304.

[0049] 15-17 illustrate an optically isolated power supply solution using the example LDO regulator device 1200 of FIG. 12 in combination with an optical ribbon or fiber 1508. FIGS. 15 and 16 show side and top views, respectively, of the isolated power supply device 1500 packaged in a molded compound material 1502. A light source side circuit 1501 includes leads 1504 and 1506, such as pins or pads, that can be soldered to a host printed circuit board (not shown), light sources (e.g., side- or lateral-emitting LEDs) 105, 108, and a leadframe structure having optical coupling material 804 connected to the input side of the optical ribbon or fiber 1508. The output end of the optical ribbon or fiber 1508 is connected to the lateral sensor surface 107b of the LMSPV structure 106 via the corresponding optical coupling material 804. The power supply device 1500 also includes a load or output side circuit 1511, which includes the LDO regulator device 1200 as described above in connection with FIG. 12. The regulator device 1200 in this example is mounted on an output lead frame structure including leads 1510 and 1512 for providing an electrical output signal (e.g., output voltage or current) to a driven load circuit connected to a host printed circuit board. The device 1500 in Figures 15 and 16 advantageously provides an optical power delivery isolation solution in a single device and advantageously uses the high power transfer ratio and high efficiency advantages of the LMSPV structure 106 to transfer power across a galvanic isolation barrier without the space, cost, and electromagnetic interference problems that are drawbacks of transformer isolation techniques for power transfer.

[0050] 17 illustrates another optical isolation system 1700 for power transfer between two remote systems. In this example, source-side circuitry 1501 is packaged within a packaged multi-die structure 1701 that includes a first integrated circuit die or leadframe structure with leads 1504 and 1506. Optical fibers or ribbons 1508 connect the first structure 1701 to a packaged multi-die structure 1702 that includes a second IC die or leadframe structure with leads 1510 and 1512 and the regulator device 1200 described above. Optical isolation system 1700 provides an integrated solution for biasing or driving a load across an isolation barrier through the simple connection of optical ribbons or fibers 1508 between die structure 1701 and die structure 1702.

[0051] FIG. 18 shows another example of a load side circuit 1511 for implementing an LDO regulator system 1800. The load side circuit 1511 in this example includes an LMSPV structure 106 and a regulator structure 1200 including a switching circuit 1202 and a regulator circuit 1204 as described above. The circuits and structures 106, 1202, and 1204 in this example are fabricated on a single semiconductor die 1200. This example also includes an optically-isolated barrier structure 1802. In one example, the optically-isolated barrier structure 1802 includes a black polymer or other light-blocking material formed in a trench in the semiconductor die. In one example, the LMSPV semiconductor structure 106, including p- and n-doped portions 101 and 103, is formed in a silicon structure along with the switching circuitry 1202 and the regulator circuitry 1204. A trench is formed to isolate the LMSPV structure 106 from the switching circuitry 1202, and the trench is filled with a black polymer. The die is then back-ground to expose the polymer in the trenches. The resulting structure is held together by the polymer, which forms an optical barrier to isolate the LMSPV structure 106 from the switching circuitry 1202 and the LDO circuitry 1204.

[0052] 19 and 20, the optical isolation techniques and barrier structures 1802 of FIG. 18 may be used in other embodiments where it is desirable to optically isolate different channels or different circuits. FIG. 19 shows another regulator system 1900 including multiple optical channels. Each channel in this example includes an LMSPV stack structure 106 that receives an optical signal via a corresponding optical fiber or ribbon 1508. In this example, black polymer-filled trench isolation structures 1802 are formed along the top and bottom edges of each of the LMSPV sensor structures 106. This effectively prevents optical crosstalk between the LMSPV sections or cells 106 and also prevents optical interference with the switching circuit 1202 and / or LDO regulator circuit elements 1204 formed in the device 1200.

[0053] FIG. 20 shows another example that includes the black polymer-filled optical isolation structure 1802 described above to confine the optical signal within the two illustrated LMSPV portions 106. In this example, a reflective material-filled structure 2002 is formed around each LMSPV portion 106 of the optical channel. As described above, the use of a reflective material increases the capture efficiency of the LMSPV structure 106 by promoting additional opportunities for photon capture within the semiconductor material and extended p-n junction. In one implementation, the reflector structure 2002 includes a straight section that spans most of the length of the LMSPV structure 106, and the back side of the LMSPV structure includes an arc section, such as a parabolic section. In one example, the structure 2002 is formed by a selective deep etching process similar to that used to form the optical isolation structure 1802. After fabrication of the LMSPV components 106, deep trenches are formed in the semiconductor structure and the trenches are filled with an optically reflective material, such as glass. The die is then back-ground to expose the glass, leaving an enhanced LMSPV structure 106 with reflective structures 2002 laterally surrounding three sides of the semiconductor structure and its extended p-n junction. Additionally, black polymer filler structures 1802 between adjacent optical channels provide optical isolation to reduce or avoid optical crosstalk between the optical channels. Additionally, as described above, reflective materials may be added to the top and bottom of each LMSPV structure 106, such as a reflective epoxy on the bottom side B and an oxide layer or material formed on the top side T (e.g., 109 in FIG. 1 ).

[0054] Referring now to FIGS. 21-23, a unique configuration of a silicon photomultiplier device (SiPMD) is shown. The present disclosure provides a SiPMD that does not use conventional methods in which photons enter the top surface of a silicon array. Instead, like the exemplary devices described above, SiPMDs allow photons to enter at the side or edge for extended collection distances. The SiPMD multiplies a single input photon into an electron avalanche in a PN cell of the array, where an electron-hole pair is generated. In the example of FIG. 21, each array cell is isolated from the next cell, so the avalanche does not propagate across the entire structure. An avalanche occurs because the cell is operated near its avalanche breakdown, so a single photon is sufficient to cause an avalanche current flow. This produces high gain amplification in each cell, making it a highly sensitive detector. Once the avalanche has been tripped, the cell needs to be reset, so there is a series quenching resistor R for each cell, as shown in Figures 22 and 23. The quenching circuit resistor R reduces the cell voltage enough to bring it out of avalanche. These cells and quenching resistors are all in parallel, so the combined output current represents the photon density multiplied by a very large gain factor, and the circuit uses a bias to operate. The lateral structure also increases the sensitivity of the detector.

[0055] FIG. 21 illustrates an example LMSPV array structure 2100 including a plurality of photosensor semiconductor structures formed in an array. The LMSPV structure 2100 includes a matrix or array of multiple individual pn cells having a lateral sensor surface 107b and an extended effective junction distance D, as described above. In this example, each cell of the array includes a single n-doped portion 103 formed in an isolated p-doped region 101 to create an array of individual pn junctions arranged across the extended effective junction distance D. FIG. 21 also illustrates a breakout view of two columns and portions of several rows of array cells in one example. Additionally, as described below in connection with FIGS. 22 and 23, the LMSPV structure 2100 can also be used in photon sensor applications.

[0056] As shown schematically in FIGS. 22 and 23 , LMSPV structures 106, whether arrays with multiple cells or single semiconductor structures 106 with a p-doped portion 101 and one or more n-doped portions 103 to form an extended junction, can be used in photon detection systems and circuits. FIG. 22 shows an example photon detector circuit 2200 with semiconductor structures 101, 103 including multiple n-doped portions 103 disposed within the p-doped portion 101, as described above. This structure forms an extended junction photosensor 106 with a lateral sensor surface 107 b for receiving photons along an optical path 114. The sensor structure 106 has an effective junction distance D equal to the absorption depth for the semiconductor structure corresponding to a given wavelength λ of the incoming optical signal multiplied by a constant K. Circuit 2300 in FIG. 23 shows a similar arrangement using an extended junction photosensor circuit 106 with a single n-doped portion 103. The photosensor in detector circuits 2200 and 2300 in Figures 22 and 23 includes an equivalent parasitic capacitor, diode, and resistor in each diode cell of the array, which form a quenching circuit, with capacitor C coupled in parallel to sensor circuit diode 111 between p-doped portion 101 and n-doped portion 103, and resistor R coupled between bias voltage V and n-doped portion 103. The resulting structure forms a quenching circuit for detecting a small number of photons, or even the receipt of a single photon, in the lateral sensor structure 106. In operation, application of a bias voltage to resistor R charges capacitor C, while sensor circuit diode 111 is reverse-biased. The bias voltage V is set to a level corresponding to the specifications of sensor circuit diode 111, so as to charge capacitor C to a level just below the avalanche rating of diode 111 (while diode 111 does not conduct). Once the parasitic capacitor C is charged, the circuit 2200 is ready to receive one or more photons at the sensor surface 107b along the optical path 114. Successful capture of an incident photon at the sensor structure 106 causes the pn junction to conduct an avalanche current, discharging the parasitic capacitor C.When the parasitic capacitor C discharges to a level below the avalanche threshold of the diode 111, the diode 111 stops conducting, and the parasitic resistor R causes the capacitor C to recharge. The discharging / charging of the parasitic capacitor C creates a signal indicative of the capture of a photon by the detector circuit 2200, 2300. A current sense threshold comparison can be used to generate a detector output signal based on this increased current flow. A sense resistor RS is connected from the + input of the comparator 2202 to the circuit ground reference to establish a voltage signal in response to a received current spike. In FIGS. 22 and 23, the p-doped portion 101 is connected to the non-inverting (+) input of the voltage comparator 2202 to receive the signal voltage. The comparator 2202 compares the signal voltage with a threshold voltage VTH to generate a detector output signal DETECT OUT in response to a current spike. Because the current signal generated by discharging / charging capacitor C is much larger than the carrier current generated in sensor structure 106 by electron-hole pair generation, circuit elements 2200, 2300 provide a photon multiplication circuit that can be used in photon detection or other useful applications. Because the detector array detects individual photons, it is also possible to use a lower-efficiency emitter for the photon source. This allows the use of standard silicon with a forward-biased silicon pn junction emitter instead of a GaAs LED for low-intensity IR radiation. Reverse-biased avalanche or Zener junctions can also be used to emit low-intensity visible light.

[0057] The disclosed examples provide a highly efficient lateral PV cell with lateral photon injection into an effective pn junction of extended length. In some examples, the effective lateral junction distance D is set to a multiple of the absorption depth of photons at a given wavelength λ to promote high collection efficiency. This significantly increases the opportunity for electron-hole pair generation in the semiconductor structure of the photosensor 106. The disclosed examples offer advantages in low-power signal transmission across the optical channel, enabling highly efficient optical transmission of power across a galvanic isolation barrier. The disclosed concepts also find utility in photon detectors or photon multipliers. In some configurations, many sensor cells 106 are interconnected for higher-level power supply, with each cell being a low-cost configuration. If individual photovoltaic cells 106 can include optically reflective material 109 on the top (T), bottom (B), backside, and lateral sides via oxide and / or reflective epoxy, a low-cost stack configuration is possible, with the negative (n-type) node connected on the top (T) by one or more bond pads and the positive (p-type) semiconductor material connected on the bottom (B). This exemplary configuration allows simple die stacking with conductive epoxy to interconnect the resulting photosensitive diodes in any desired manner. The disclosed example offers potentially significant efficiency improvements for photon-to-electrical power transfer compared to conventional optical isolation techniques and devices. Furthermore, lateral photon transfer easily accommodates different isolation voltage ratings by controlling the spacing between the light source 108 and the light sensor 106, with the ability to provide any suitable optical transmission medium (e.g., glass, air, polymer), and by using optical fiber or optical ribbon to separate the light source and sensor by a large distance, extremely large voltage isolation ratings can be achieved.

[0058] The foregoing examples are merely illustrative of some possible embodiments of various aspects of the present disclosure, and equivalent modifications and / or variations will occur to those skilled in the art upon reading and understanding this specification and the accompanying drawings. Changes are possible in the described embodiments, and other embodiments are possible, within the scope of the claims.

Claims

1. An isolation circuit, a light source configured to generate an optical signal of a given wavelength along an optical path; an optical sensor spaced an optical channel distance from the light source, The top and The bottom and a front side at least partially facing the optical path to receive the optical signal; a back side spaced from the front side; a plurality of side surfaces extending vertically between the top and bottom sides, the plurality of side surfaces extending horizontally between the front side and the back side; a plurality of p-doped portions including a p-type dopant, the plurality of p-doped portions extending along at least a portion of the bottom portion; a plurality of n-doped portions comprising an n-type dopant, each n-doped portion at least partially adjacent to a respective p-doped portion so as to form a plurality of p-n junctions extending an effective junction distance between the front side and the back side; a reflective material on at least one of the top, bottom, backside, and side surfaces; the optical sensor, a switching circuit for electrically interconnecting the plurality of pn junctions; an isolation circuit,

2. 2. The isolation circuit of claim 1, an isolation circuit, wherein the effective junction distance is greater than a constant K times the absorption depth for the optical sensor corresponding to the given wavelength, where K is 5 or greater;

3. 3. The isolation circuit according to claim 2, An isolation circuit in which K is 10 or greater.

4. 3. The isolation circuit according to claim 2, An isolation circuit in which K is 20 or more.

5. 2. The isolation circuit of claim 1, The isolated circuit, wherein the optical sensor comprises silicon.

6. 2. The isolation circuit of claim 1, The isolation circuit further includes a regulator circuit for providing a power supply signal based on an electrical signal from the optical sensor.

7. 2. The isolation circuit of claim 1, a leadframe structure including a plurality of electrical conductors, the light source being electrically coupled to a first pair of the electrical conductors of the leadframe structure and the light sensor being electrically coupled to a second pair of the electrical conductors of the leadframe structure; a molded package structure encapsulating the light source, the light sensor, and a portion of the lead frame structure, the molded package structure exposing portions of the first and second pairs of electrical conductors to allow external connections to the light source and the light sensor; an isolation circuit further comprising:

8. 8. The isolation circuit of claim 7, The isolation circuit further includes an optical transmission medium disposed along the optical path between the light source and the light sensor.

9. An isolation circuit, a light source configured to generate an optical signal of a particular wavelength along an optical path; an optical sensor spaced an optical channel distance from the light source, The top and The bottom and a front side at least partially facing the optical path to provide a sensor surface for receiving the optical signal; a back side spaced from the front side; a plurality of side surfaces extending vertically between the top and bottom sides, the plurality of side surfaces extending horizontally between the front side and the back side; a plurality of p-doped portions including a p-type dopant, the plurality of p-doped portions extending along at least a portion of the bottom portion; a plurality of n-doped portions comprising an n-type dopant, each n-doped portion at least partially adjacent to a respective p-doped portion so as to form a plurality of p-n junctions extending an effective junction distance between the front side and the back side, the effective junction distance being greater than a constant K times an absorption depth for the photosensor corresponding to the particular wavelength, where K is 5 or greater; a reflective material on at least one of the top, bottom, backside, and side surfaces; a capacitor coupled between the plurality of p-doped portions and the plurality of n-doped portions; a resistor coupled between a bias voltage terminal and the plurality of n-doped portions, the resistor charging the capacitor to a voltage that biases the plurality of pn junctions near an avalanche voltage to enable capture of photons by the plurality of pn junctions, conducting an avalanche current through the plurality of pn junctions and discharging the capacitor to generate a signal representative of the capture of the photon; the optical sensor, a switching circuit for electrically interconnecting the plurality of pn junctions; an isolation circuit,

10. an optical sensor circuit for detecting an optical signal of a particular wavelength along an optical path, An optical sensor, The top and The bottom and a front side at least partially facing the optical path; a back side spaced from the front side; a plurality of side surfaces extending vertically between the top and bottom sides, the side surfaces extending horizontally between the front side and the back side; a reflective material on at least one of the top, bottom, backside, and side surfaces; a plurality of pn junctions formed in the optical sensor, the plurality of pn junctions extending between the front side and the back side by an effective junction distance greater than a constant K times an absorption depth corresponding to the particular wavelength, where K is 5 or greater; the optical sensor, a switching circuit for electrically interconnecting the plurality of pn junctions; a light sensor circuit including:

11. 11. The optical sensor circuit of claim 10, The photosensor circuit further includes a regulator circuit for providing a power supply signal based on electrical signals from the plurality of pn junctions.

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