# Patent

## Title
Interface protection device with integrated supply clamp and method of forming the same

## Abstract

Protection circuit architectures with integrated supply clamps and methods of forming the same are provided herein. In certain implementation, an integrated circuit interface protection device includes a first diode protection structure and a first thyristor protection structure electrically connected in parallel between a signal pin a power high supply. Additionally, the protection device includes a second diode protection structure and a second thyristor protection structure electrically connected in parallel between the signal pin and a power low supply. Furthermore, the protection device includes a third diode protection structure and a third thyristor protection structure electrically connected in parallel between the power high supply and the power low supply. The third thyristor protection structure and the third diode protection structure are synthesized as part of the integrated circuit interface and can share at least a portion of the wells and/or diffusion regions associated with the first and second thyristor protection structures.

## Background
CROSS-REFERENCE TO RELATED APPLICATIONS
The present application claims priority to U.S. Provisional Patent Application No. 61/739,645, filed Dec. 19, 2012, titled “INTERFACE PROTECTION DEVICE WITH INTEGRATED SUPPLY CLAMP AND METHOD OF FORMING THE SAME,” the entirety of which is hereby incorporated herein by reference.


BACKGROUND
1. Field
Embodiments of the invention relate to electronic systems, and more particularly, to protection architectures for mixed-signal integrated circuits (ICs).
2. Description of the Related Technology
Certain electronic systems can be exposed to a transient electrical event, or an electrical signal of a relatively short duration having rapidly changing voltage and high power. Transient electrical events can include, for example, electrostatic discharge (ESD) events.
Transient electrical events can damage integrated circuits (ICs) inside an electronic system due to overvoltage conditions and/or high levels of power dissipation over relatively small areas of the ICs. High power dissipation can increase IC temperature, and can lead to numerous problems, such as gate oxide punch-through, junction damage, metal damage, and surface charge accumulation. Moreover, transient electrical events can induce latch-up (in other words, inadvertent creation of a low-impedance path), thereby disrupting the functioning of the IC and potentially causing permanent damage to the IC. Thus, there is a need to provide an IC with protection from such transient electrical events, such as during IC power-up and power-down conditions.
SUMMARY
In one embodiment, an integrated circuit is provided. The integrated circuit includes a power high pin configured to receive a first supply voltage, a power low pin configured to receive a second supply voltage, and a signal pin configured to receive a signal. The integrated circuit further includes a first NPN bipolar transistor including an emitter electrically connected to the signal pin and a first PNP bipolar transistor including an emitter electrically connected to the power high pin. The first PNP bipolar transistor and the first NPN bipolar transistor are cross-coupled and configured to operate as a first thyristor protection structure between the power high pin and the signal pin. The integrated circuit further includes a second NPN bipolar transistor including an emitter electrically connected to the power low pin, a third NPN bipolar transistor including an emitter electrically connected to the power low pin, and a second PNP bipolar transistor including an emitter electrically connected to the signal pin. The second PNP bipolar transistor and the third NPN bipolar transistor are cross-coupled and configured to operate as a second thyristor protection structure between the signal pin and the power low pin. Additionally, the first PNP bipolar transistor and the second NPN bipolar transistor are cross-coupled and configured operate as a third thyristor protection structure between the power high pin and the power low pin.
In another embodiment, a method of forming an integrated circuit is provided. The method includes providing a first thyristor structure between a power high pin and a signal pin. The first thyristor structure is associated with a first NPN bipolar transistor and a first PNP bipolar transistor, and the first NPN bipolar transistor and the first PNP bipolar transistor are cross-coupled. The method further includes providing a second thyristor structure between the power high pin and the power low pin. The second thyristor structure is associated with a second NPN bipolar transistor and the first PNP bipolar transistor, and the second NPN bipolar transistor and the first PNP bipolar transistor are cross-coupled. The method further includes providing a third thyristor structure between the signal pin and a power low pin. The third thyristor structure is associated with a third NPN bipolar transistor and a second PNP bipolar transistor. The third NPN bipolar transistor and the second PNP bipolar transistor are cross coupled.
In another embodiment, an apparatus is provided. The apparatus includes a substrate, a first well region of a first type in the substrate, a second well region of the first type in the substrate adjacent the first well region, and a third well region of a second type opposite the first type. The third well region positioned in the substrate between the first and second well regions. The apparatus further includes a fourth well region of the second type positioned on a side of the first well region that is opposite the third well region. The apparatus further includes a first diffusion region of the first type in the fourth well region, a second diffusion region of the second type in the first well region, a third diffusion region of the first type in the third well region, and a fourth diffusion region of the second type in the second well region. The first diffusion region, the fourth well region, the first well region, and the second diffusion region are configured to operate as a first thyristor structure. Additionally, the third diffusion region, the third well region, the second well region, and the fourth diffusion region are configured to operate as a second thyristor structure. Furthermore, the second diffusion region, the first well region, the third well region and the third diffusion region are configured to operate as a third thyristor structure.



BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a schematic block diagram of one embodiment of an integrated circuit.
FIG. 2A is a top plan view of a protection device according to one embodiment.
FIG. 2B is a cross section of the protection device of FIG. 2A taken along the lines 2B-2B.
FIG. 2C is an annotated cross section of the protection device of FIG. 2A taken along the lines 2B-2B.
FIG. 3 is a circuit diagram of the protection device of FIGS. 2A-2C.
FIG. 4A is a top plan view of a protection device according to another embodiment.
FIG. 4B is a cross section of the protection device of FIG. 4A taken along the lines 4B-4B.
FIG. 4C is a circuit diagram of the protection device of FIGS. 4A-4B.
FIGS. 5-10 are cross sections of various embodiments of protection devices.
FIG. 11A is an annotated cross section of a protection device according to another embodiment.
FIG. 11B is a circuit diagram of the protection device of FIG. 11A.
FIGS. 12-20 are cross sections of various embodiments of protection devices.



DETAILED DESCRIPTION OF EMBODIMENTS
The following detailed description of embodiments presents various descriptions of specific embodiments of the invention. However, the invention can be embodied in a multitude of different ways as defined and covered by the claims. In this description, reference is made to the drawings where like reference numerals may indicate identical or functionally similar elements.
Terms such as above, below, over and so on as used herein refer to a device orientated as shown in the figures and should be construed accordingly. It should also be appreciated that because regions within a semiconductor device (such as a transistor) are defined by doping different parts of a semiconductor material with differing impurities or differing concentrations of impurities, discrete physical boundaries between different regions may not actually exist in the completed device but instead regions may transition from one to another. Indeed, the higher dopant concentration regions of semiconductor devices are known as diffusion regions because the dopants tend to at least be partially defined by diffusion and thus by their very nature do not have sharp boundaries. Some boundaries as shown in the accompanying figures are of this type and are illustrated as abrupt structures merely for the assistance of the reader. In the embodiments described below, p-type regions can include a semiconductor material with a p-type dopant, such as boron. Further, n-type regions can include a semiconductor material with an n-type dopant, such as phosphorous. Further, gate dielectric can include insulators, such as high k-dielectric. Further, gates can include conductive regions with variable work functions, such as variable work-function metal or polysilicon. A skilled artisan will appreciate various concentrations of dopants, conductive materials and insulating material can be used in regions described below.
Overview of Protection Devices
To help assure that an electronic system is reliable, manufacturers can test the electronic system under defined stress conditions, which can be described by standards set by various organizations, such as the Joint Electronic Device Engineering Council (JEDEC), the International Electrotechnical Commission (IEC), and the International Organization for Standardization (ISO). The standards can cover a wide multitude of transient electrical events as discussed above, including electrostatic discharge (ESD) events.
Electronic circuit reliability is enhanced by providing protection devices to the pins or pads of an IC. The protection devices can maintain the voltage level at the pins within a predefined safe range by transitioning from a high-impedance state to a low-impedance state when the voltage of the transient signal reaches a trigger voltage. Thereafter, the protection device can shunt at least a portion of the current associated with the transient signal to prevent the voltage of the transient signal from reaching a positive or negative failure voltage that is one of the most common causes of IC damage.
Certain protection schemes can use separate protection devices to protect an IC's signal pin, such as an input and/or output signal pin, and a separate power supply clamp to provide protection between the IC's power high and power low supplies.
Protection devices with integrated supply clamps and methods of forming the same are provided herein. In certain implementation, a protection device includes a first diode protection structure for protecting an IC against transient electrical events that cause the voltage of a signal pin of the IC to increase relative to the voltage of a power high supply, and a first thyristor protection structure for protecting against transient electrical events that cause the voltage of the signal pin to decrease relative to the voltage of the power high supply. Additionally, the protection device includes a second diode protection structure for protecting against transient electrical events that cause the voltage of the signal pin to decrease relative to the voltage of a power low supply, and a second thyristor protection structure for protecting against transient electrical events that cause the voltage of the signal pin to increase relative to the voltage of the power low supply. The protection device further includes an integrated supply clamp that provides protection between the IC's power high and power low supplies. The integrated supply clamp includes a third thyristor protection structure for protecting the IC when a transient electrical event causes the voltage of the power high supply to increase relative to the voltage of the power low supply, and a third diode protection structure for protecting the IC when a transient electrical event causes the voltage of the power high supply to decrease relative to the voltage of the power low supply. The third thyristor protection structure and the third diode protection structure can share at least a portion of the wells and/or diffusion regions associated with the first and second thyristor protection structures so as to enable multi-domain self-contained mixed-signal IO protection and/or reduce the protection circuit's area relative to a configuration using a supply clamp implemented in a separate layout.
The protection devices described herein can be used to enhance design flexibility by eliminating a need for separate power supply clamps between power high and power low supplies. Additionally, in some embodiments such protection devices can also alleviate a need for power supply clamps between independent power supply domains or across power supply domains in multi-supply configurations. The protection devices can aid in providing an integrated protection solution for ICs fabricated using a variety of processes, including, for example, sub-28 nm CMOS metal-gate processes.
FIG. 1 is a schematic block diagram of one embodiment of an integrated circuit 30. The integrated circuit or IC 30 includes a first protection device 1a, a second protection device 1b, a third protection device 1c, a first signal pin or pad 2a (IO-1), a second signal pin 2b (IO-2), a third signal pin 2c (IO-3), a first power low pin 3a (VSS1), a second power low pin 3b (VSS2), a third power low pin 3c (VSS3), a first power high pin 4a (VDD1), a second power high pin 4b (VDD2), a third power high pin 4c (VDD3), a substrate supply pin 5 (VSUB), a receiver 6, a first transmitter or driver 7a, a second driver 7b, a resistor 8, a diode 9, a first anti-parallel diode structure 10a, and a second anti-parallel diode structure 10b. 
The integrated circuit 30 illustrates one example of an integrated circuit that can include one or more of the protection devices described herein. However, the protection devices can be used in other integrated circuit configurations, including, for example, implementations of integrated circuits using more or fewer protection devices, signal pins, and/or power supply domains. For example, protection devices can be used to protect one or more signal pins of an IC that includes a single power supply domain.
The illustrated integrated circuit 30 includes independent power supply domains, or power supply domains associated with different power high and power low supply pins or pads. The independent power supply domains can be used to enhance noise isolation between different power domains and/or to permit the power supply domains to operate with different electrical potentials or voltages. For example, the integrated circuit 30 includes a first power supply domain associated with the first signal pin 2a and the first power low and power high pins 3a, 4a, a second power supply domain associated with the second signal pin 2b and the second power low and power high pins 3b, 4b, and a third power supply domain associated with the third signal pin 2c and the third power low and power high pins 3c, 4c. In one embodiment, the first power supply domain is a 0.9 V domain and at least one of the second or third power supply domains is a domain having a voltage in the range of about 1.8 V to about 3.3 V. However, other configurations are possible.
The first to third protection devices 1a-1c can be used to provide transient electrical event protection such as ESD protection to the first to third power supply domains. For example, the first protection device 1a can protect circuitry associated with the first power supply domain, such as the receiver 6, from ESD events received between the first signal pin 2a and the first power low pin 3a, between the first signal pin 2a and the first power high pin 4a, and/or between the first power low pin 3a and the first power high pin 4a. Additionally, the second protection device 1b can protect circuitry associated with the second power supply domain from ESD events received between the second signal pin 2b and the second power low pin 3b, between the second signal pin 2b and the second power high pin 4b, and/or between the second power low pin 3b and the second power high pin 4b. Furthermore, the third protection device 1c can protect circuitry associated with the third power supply domain from ESD events received between the third signal pin 2c and the third power low pin 3c, between the third signal pin 2c and the third power high pin 4c, and/or between the third power low pin 3c and the third power high pin 4c. 
In the illustrated configuration, the first signal pin 2a is electrically connected to an input of the receiver 6, and the second and third signal pins 2b, 2c are electrically connected to outputs of the first and second drivers 7a, 7b, respectively. However, other configurations are possible, including configurations using a different implementation of input and/or output circuitry. Indeed, the protection devices described herein can be used to protect input or receive pins, output or transmit pins, and/or input/output or bidirectional pins.
Each of the first to third protection circuits 1a-1c includes a first thyristor protection structure 11, a second thyristor protection structure 12, a third thyristor protection structure 13, a first diode protection structure 21, a second diode protection structure 22, a third diode protection structure 23, and a fourth diode protection structure 24.
The first diode protection structure 21 can protect against transient electrical events that cause the voltage of a signal pin to increase relative to the voltage of an associated power high supply, and the first thyristor protection structure 11 can protect against transient electrical events that cause the voltage of the signal pin to decrease relative to the voltage of the power high supply. For example, the first diode protection structure 21 and the first thyristor protection structure 11 of the first protection device 1a can be used to provide protection against ESD events received between the first signal pin 2a and the first power high pin 4a. Similarly, the first diode protection structure 21 and the first thyristor protection structure 11 of the second protection device 1b can protect against ESD events received between the second signal pin 2b and the second power high pin 4b, and the first diode protection structure 21 and the first thyristor protection structure 11 of the third protection device 1c can be used to provide protection against ESD events received between the third signal pin 2c and the third power high pin 4c. 
The second diode protection structure 22 can protect against transient electrical events that cause the voltage of a signal pin to decrease relative to the voltage of an associated power low supply, and the second thyristor protection structure 12 can protect against transient electrical events that cause the voltage of the signal pin to increase relative to the voltage of the power low supply. Additionally, the third diode protection structure 23 can protect against transient electrical events that cause the voltage of a power high supply to decrease relative to the voltage of an associated power low supply, and the third thyristor protection structure 13 can protect against transient electrical events that cause the voltage of the power high supply to increase relative to the voltage of the power low supply. As will be described in detail further below, the third thyristor protection structure 13 and the third diode protection structure 23 can share at least a portion of the wells and/or diffusion regions associated with the first and second thyristor protection structures 11, 12 so as to enable multi-domain self-contained mixed-signal IO protection and/or reduce the protection circuit's area relative to a configuration using a separate supply clamp.
The first to third protection devices 1a-1c can also each include the fourth diode protection structure 24. In certain configuration, the fourth diode protection structure 24 can be electrically connected in parallel with the third diode protection structure 23, as illustrated in FIG. 1 for the second and third protection devices 1b, 1c. For example, the third and fourth diode protection structures 23, 24 of the second protection device 1b have been electrically connected in parallel between the second power high pin 4b and the second power low pin 3b. Connecting the fourth diode protection structure 24 in parallel with the third diode protection structure 23 can increase the current handling capability of the protection device against ESD events received between power high and power low supplies. However, the fourth diode protection structure 24 can be connected in other ways. For example, the fourth diode protection structure 24 of the first protection device 1a has been electrically connected between the first power high pin 4a and the substrate supply pin 5, which can function as a guard ring to reduce substrate majority carrier injection and reduce the likelihood of latch-up during normal operation or during ESD events when the integrated circuit is powered.
In certain implementations, the IC's power supply domains can be interconnected using power low decoupling circuits and/or power high decoupling circuits. For example, in the illustrated configuration, the first power low pin 3a is electrically connected to the second power low pin 3b using the first anti-parallel diode structure 10a, and the second power low pin 3b is electrically connected to the third power low pin 3c using the second anti-parallel diode structure 10b. Additionally, the first power high pin 4a is electrically connected to the second power high pin 4b using the diode 9. Interconnecting the IC's power supply domains using power low and/or power high decoupling circuits may provide multiple protection paths to an IC during a transient electrical event, since stress current can be injected from one pin to another pin in a different power supply domain through the decoupling circuits during the transient electrical event. Accordingly, in certain implementations, more than one of the protection circuits 1a-1c can activate during a transient electrical event. Although FIG. 1 illustrates a particular configuration of power high and power low decoupling circuits, other configurations are possible. Additionally, in certain implementations one or more of the power high and/or power low decoupling circuits can be omitted, added, or arranged in other ways.
Furthermore, in certain configurations, a voltage used to bias the substrate can be coupled to one or more of the power supply domains. For example, in FIG. 1 the resistor 8 has been electrically connected between the substrate supply pin 5 and the first power low pin 3a. However, other configurations are possible, such as implementations in which the substrate supply pin 5 is connected in other ways or implementations in which the substrate supply pin 5 is omitted in favor of biasing the substrate using one or more of the first to third power low pins 3a-3c. 
The protection devices 1a-1c each include an integrated supply clamp for providing protection to the IC 30 against transient electrical events received between power high and power low supplies. The integrated supply clamp includes the third thyristor protection structure 13 and the third diode protection structure 23. Configuring the protection devices 1a-1c to include the integrated supply clamp can reduce the IC's overall circuit area, as well as help localize control of a clamping condition between the power rails or supplies at the signal pins, in particular for precision low voltage mixed-signal applications. Additionally, the illustrated configuration permits protection devices associated with a particular domain and/or signal pin to be configured separately from other protection devices, thereby providing a capability of independently optimizing the protection devices for high performance applications.
Various embodiments of protection devices that can be used to implement the first, second, and/or third protection circuits 1a-1c will be described below with reference to FIGS. 2A to 20. Although the protection devices have been described in the context of the integrated circuit 30 of FIG. 1, the protection devices can be used in other configurations of integrated circuits.
FIG. 2A a top plan view of a protection device 40 according to one embodiment. FIG. 2B is a cross section of the protection device 40 of FIG. 2A taken along the lines 2B-2B. FIG. 2C is an annotated cross section of the protection device 40 of FIG. 2A taken along the lines 2B-2B.
The protection device 40 includes a p-well 42, a first n-well 43a, a second n-well 43b, first to eighth p-type diffusion or P+ regions 44a-44h, first to sixth n-type diffusion or N+ regions 45a-45f, first to ninth gate regions 46a-46i, and oxide regions 48. The first to ninth gate regions 46a-46i can each include a conductive gate and a gate insulator, such as a thin oxide layer. For purposes of clarity, the oxide regions 48 have been omitted from the top plan view of FIG. 2A. The illustrated protection device 40 is fabricated in a p-type substrate 49. However, the teachings herein are applicable to other types of substrates. For example, the teachings herein are applicable to configurations using an n-type substrate in which the polarity of the illustrated active and well regions uses the opposite doping type.
As shown in FIG. 2A, the p-well 42 is disposed in the p-type substrate 49, and the first and second n-wells 43a, 43b are configured as adjacent islands in the p-well 42. Additionally, the first P+ region 44a and the first N+ region 45a are disposed in a first or left region of the p-well 42 adjacent a first side of the first n-well 43a, with the first N+ region 45a positioned between the first P+ region 44a and the first n-well 43a. Furthermore, the fourth N+ region 45d is disposed in a second or central region of the p-well 42 between a first side of the second n-well 43b and a second side of the first n-well 43a that is opposite the first side. Additionally, the seventh P+ region 44g is disposed in a third or right region of the p-well 42 adjacent a second side of the second n-well 43b that is opposite the first side. The fourth P+ region 44d extends along the second side of the first n-well 43a, and includes a first portion in the first n-well 43a and a second portion in the central region of the p-well 42. The fifth P+ region 44e extends along the first side of the second n-well 43b, and includes a first portion in the central region of the p-well 42 and a second portion in the second n-well 43b. The second P+ region 44b, the second N+ region 45b, the third P+ region 44c, and the third N+ region 45c are disposed in the first n-well 43a. The second P+ region 44b is positioned between the first and second N+ regions 45a, 45b, and the third P+ region 44c is positioned between the second and third N+ regions 45b, 45c. Additionally, the second N+ region 45b is positioned between the second and third P+ regions 44b, 44c, and the third N+ region 45c is positioned between the third and fourth P+ regions 44c, 44d. Additionally, the fifth N+ region 45e, the sixth P+ region 44f, and the sixth N+ region 45f are disposed in the second n-well 43b. The fifth N+ region 45e is positioned between the fifth and sixth P+ regions 44e, 44f, and the sixth N+ region 45f is positioned between the sixth and seventh P+ regions 44f, 44g. Additionally, the sixth P+ region 44f is positioned between the fifth and sixth N+ regions 45e, 45f The eighth P+ region 44h has been configured as a ring that surrounds the first and second n-wells 43a, 43b, the first to sixth N+ regions 45a-45f, and the first to seventh P+ regions 44a-44g. 
The protection device 40 includes the first to ninth gate regions 46a-46i, which can operate as implant blocking regions that define the position of certain diffusion regions. The first gate region 46a extends over the left region of the first p-well 42 between the first P+ region 44a and the first N+ region 45a. Additionally, the second gate region 46b extends over the left region of the p-well 42 and the first n-well 43a between the first N+ region 45a and the second P+ region 44b. Furthermore, the third gate region 46c extends over the first n-well 43a between the third P+ region 44c and the third N+ region 45c. Additionally, the fourth gate region 46d extends over the first n-well 43a between the third N+ region 45c and the fourth P+ region 44d. Furthermore, the fifth gate region 46e extends over the central region of the p-well 42 between the fourth P+ region 44d and the fourth N+ region 45d. Additionally, the sixth gate region 46f extends over the central region of the p-well 42 between the fourth N+ region 45d and the fifth P+ region 44e. Furthermore, the seventh gate region 46g extends over the second n-well 43b between the fifth P+ region 44e and the fifth N+ region 45e. Additionally, the eighth gate region 46h extends over the second n-well 43b between the fifth N+ region 45e and the sixth P+ region 44f Furthermore, the ninth gate region 46i extends over the second n-well 43b between the sixth P+ region 44f and the sixth N+ region 45f. 
In certain implementations, the first to ninth gate regions 46a-46f are implemented using metal. However, other configurations are possible, such as implementations in which the gates are made out of materials that are not metals, such as poly silicon. In certain implementations, the gate regions include a conductive structure and a dielectric structure such as silicon dioxide or a high-k dielectric.
The illustrated protection device 40 includes the oxide regions 48. Formation of the oxide or isolation regions 48 can involve etching trenches in the p-type substrate 49, filling the trenches with a dielectric, such as silicon dioxide (SiO2), and removing the excess dielectric using any suitable method, such as chemical-mechanical planarization. In certain implementations, the oxide regions 48 can be shallow trench regions disposed between certain active regions.
As shown in FIG. 2A, the first to seventh P+ regions 44a-44g, the first to sixth N+ regions 45a-45f, and the first to ninth gate regions 46a-46i can be configured to extend in a first or vertical direction. Configuring the device in this manner can aid in controlling the flow of current during activation of the protection device 40 in a second or horizontal direction.
In certain configurations, the protection device 40 can be implemented using a plurality of sub-cells or building blocks that are connected to operate as the protection device. For example, in the configuration of FIGS. 2A-2C, the protection device 40 has been implemented using three sub-cells replicated in the vertical direction, which can be connected to one another using metal layers and contacts. Implementing the protection device using sub-cells can aid in providing enhanced performance by providing a structure having enhanced manufacturing process control relative to a single cell configuration. For example, using multiple sub-cells can reduce part-to-part variation in the protection device associated with fine process features or misalignment within manufacturing constraints. Such variation can affect standing leakage, current handling capability and breakdown characteristics. Using multiple sub-cells can reduce variation relative to a configuration using a single sub-cell, which can have a relatively large amount of manufacturing variation in certain processes. Although the protection device 40 has been illustrated as including three sub-cells, the protection device 40 can include more or fewer sub-cells.
As shown in FIG. 2A, the eighth P+ region 44h can be implemented as a ring that surrounds N+ regions, P+ regions, and gate regions associated with each of the sub-cells. The eighth P+ region 44h can operate as a guard ring for reducing the injection of charge from the protection device 40 into the substrate.
Although FIG. 2A illustrates one possible top or plan view of the protection device 40, other configurations are possible, such as configurations including more or fewer sub-cells and/or configurations including a different arrangements of wells, gates, and/or diffusions regions. For example, in one embodiment, the left, center, and right regions of the p-well 42 are implemented using multiple p-wells.
With reference to FIGS. 2B-2C, the cross-sections of the protection device 40 have been annotated to schematically depict various electrical connections between the protection device 40 and the signal pin 2, a power high supply VDD, a power low supply VSS, and a substrate supply VSUB. In the illustrated configuration, the second gate region 46b, the second P+ region 44b, the second N+ region 45b, the third P+ region 44c, and the sixth N+ region 45f are electrically connected to the power high supply VDD. Additionally, the first P+ region 44a, the fourth N+ region 45d, and the seventh P+ region 44g are electrically connected to the power low supply VSS. Furthermore, the eighth P+ region 44h is electrically connected to the substrate supply VSUB. Additionally, the first N+ region 45a and the sixth P+ region 44f are electrically connected to the signal pin 2. The illustrated electrical connections can be made, for example, using contact and metal layers, such as those associated with metallization or back-end processing.
In the illustrated configuration, the first gate region 46a and the third to ninth gate regions 46c-46i are electrically floating. The first gate region 46a and the third to ninth gate regions 46c-46i do not operate as gates of metal oxide semiconductor (MOS) transistors in this configuration, since active areas of different doping polarities have been formed on opposing sides of the gate regions. However, the first gate region 46a and the third to ninth gate regions 46c-46i have been advantageously used to operate as implant blocking regions to allow more uniform current conduction and faster response during transient stress conditions. The second gate region 46b can be associated with MOS transistors, as will be described in further detail below with reference to FIGS. 11A-11B. For example, the protection device 40 can include an NFET transistor having a gate associated with the second gate region 46b, a source associated with the first N+ region 45a, a drain associated with the first n-well 43a, and a body associated with the left region of the p-well 42. Additionally, the protection device 40 can include a PFET transistor having a gate associated with the second gate region 46b, a source associated with the second P+ region 44b, a drain associated with the left region of the p-well 42, and a body associated with the first n-well 43a. Additional details of the FET structures will be described in detail further below with reference to FIGS. 11A-11B.
The substrate supply VSUB has been electrically connected to the eighth P+ region 44h, which in certain implementations can be positioned along an outer perimeter of the protection device 40 to operate as a guard ring. Connecting the substrate supply VSUB to the eighth P+ region 44h can reduce carrier injection and/or the risk of latch-up when the protection device is integrated on-chip. In one embodiment, the eighth P+ region 44h is Kelvin-connected to a pin that supplies the substrate supply VSUB. For example, the eighth P+ region 44h can be connected such that a resistance between the eighth P+ region 44h and the substrate pin is greater than a resistance between the p-type substrate 49 and the substrate pin. Although the protection device 40 is illustrated as including both the substrate supply VSUB and the power low supply VSS, other configurations are possible, including, for example, implementations in which the substrate supply VSUB is omitted in favor of electrically connecting the eighth P+ region 44h to the power low supply VSS.
In certain implementations, a common VSS pin is used to supply both the power low supply VSS and the substrate supply VSUB, but the substrate supply VSUB is Kelvin-connected to the VSS pin. By using an independent or separate Kelvin connection in metal from the eighth P+ region 44h to the VSS pin, a power low supply connection to the protection device 40 can be optimized to handle high current during an ESD event. For example, the protection device's power low supply connection can be independently connected in wide metal from the VSS pin to the terminals of the device, for instance to the first and seventh P+ regions 44a, 44g and to the fourth N+ region 45d. By configuring the protection device in this manner, the substrate supply VSUB can be independently provided via Kelvin-connection to the eighth P+ region 44h, thereby minimizing the voltage potential difference that can be generated during a high current discharge between the location of the protection device 40 on chip and the VSS pin. Additionally, configuring the device in this manner can help prevent latchup-induced damage into a powered integrated circuit formed in the common substrate, as latchup can be associated with large substrate voltage differences and large charge injection into the substrate 49 via the p-well 42 during an ESD event or during TO current injection latchup testing.
The protection device 40 of FIG. 2C has been annotated to show certain equivalent circuit devices formed from the illustrated structure, such as a first NPN bipolar transistor 51, a second NPN bipolar transistor 52, a third NPN bipolar transistor 53, a first resistor 57, a second resistor 58, a third resistor 59, a first PNP bipolar transistor 61, a second PNP bipolar transistor 62, a first diode 63, and a second diode 64.
The first NPN bipolar transistor 51 includes an emitter associated with the first N+ region 45a, a base associated with the left region of the p-well 42, and a collector associated with the first n-well 43a. The second NPN bipolar transistor 52 includes an emitter associated with the fourth N+ region 45d, a base associated with the central region of the p-well 42, and a collector associated with the first n-well 43a. The third NPN bipolar transistor 53 includes an emitter associated with the fourth N+ region 45d, a base associated with the central region of the p-well 42, and a collector associated with the second n-well 43b. The first PNP bipolar transistor 61 includes an emitter associated with the second P+ region 44b, a base associated with the first n-well 43a, and a collector associated with the p-type substrate 49. The second PNP bipolar transistor 62 includes an emitter associated with the sixth P+ region 44f, a base associated with the second n-well 43b, and a collector associated with the p-type substrate 49. The first diode 63 includes a cathode associated with the first and second n-wells 43a, 43b and an anode associated with the p-well 42 and the first and seventh P+ regions 44a, 44g. The second diode 64 includes a cathode associated with the first and second n-wells 43a, 43b and an anode associated with the p-well 42 and the eighth P+ region 44h. 
The first resistor 57 is associated with a resistance of the p-well 42 between the power low supply VSS and the collector of the second PNP bipolar transistor 62. The second resistor 58 is associated with a resistance of the p-type substrate 49 between the collector of the first PNP bipolar transistor 61 and the bases of the second and third NPN bipolar transistors 52, 53. The third resistor 59 is associated with a resistance of the first n-well 43a between the power high supply VDD and the base of the first PNP bipolar transistor 61.
FIG. 3 is a circuit diagram 50 of the protection device 40 of FIGS. 2A-2C. The circuit diagram 50 includes the first NPN bipolar transistor 51, the second NPN bipolar transistor 52, the third NPN bipolar transistor 53, the first resistor 57, the second resistor 58, the third resistor 59, the first PNP bipolar transistor 61, the second PNP bipolar transistor 62, the first diode 63, and the second diode 64, which can be as described earlier with reference to FIG. 2C. The circuit diagram 50 illustrates various connections between the components and the signal pin 2, the power high supply VDD, the power low supply VSS, and the substrate supply VSUB.
The first resistor 57 includes a first end electrically connected to the power low supply VSS and a second end electrically connected to a first end of the second resistor 58, to a base of the second NPN bipolar transistor 52, to a base of the third NPN bipolar transistor 53, to a collector of the second PNP bipolar transistor 62. The second resistor 58 further includes a second end electrically connected to the power low supply VSS. The third resistor 59 includes a first end electrically connected to the power high supply VDD and a second end electrically connected to a collector of the first NPN bipolar transistor 51, to a collector of the second NPN bipolar transistor 52, and to a base of the first PNP bipolar transistor 61. The first NPN bipolar transistor 51 further includes an emitter electrically connected to the signal pin 2 and a base electrically connected to the power low supply VSS. The second NPN bipolar transistor 52 further includes an emitter electrically connected to the power low supply VSS. The third NPN bipolar transistor 53 further includes an emitter electrically connected to the power low supply VSS and a collector electrically connected to power high supply VDD. The first PNP bipolar transistor 61 further includes an emitter electrically connected to the power high supply VDD and a collector electrically connected to the power low supply VSS. The second PNP bipolar transistor 62 further includes a base electrically connected to the power high supply VDD and an emitter electrically connected to the signal pin 2. The first diode 63 includes a cathode electrically connected to the power high supply VDD and an anode electrically connected to the power low supply VSS. The second diode 64 includes a cathode electrically connected to the power high supply VDD and an anode electrically connected to the substrate supply VSUB.
With reference to FIGS. 2A-3, the protection device 40 can be used to protect against various transient electrical events. For example, the protection device 40 includes a first diode protection structure 21 associated with an emitter-base junction of the second PNP bipolar transistor 62, which can correspond to a junction between the sixth P+ region 44f and the second n-well 43b of FIG. 2A-2C. The first diode protection structure 21 can be used to protect an IC against transient electrical events that cause the voltage of the signal pin 2 to increase relative to the voltage of the power high supply VDD. Additionally, the protection device 40 further includes a first thyristor protection structure or PNPN silicon controlled rectifier (SCR) structure 11 associated with the first NPN bipolar transistor 51 and the first PNP bipolar transistor 61, which are cross-coupled. The first thyristor protection structure 11 can correspond to the PNPN structure of the second P+ region 44b, the first n-well 43a, the left region of the p-well 42, and the first N+ region 45a of FIG. 2A-2C. The first thyristor protection structure 11 can be used to protect the IC against transient electrical events that cause the voltage of the signal pin 2 to decrease relative to the voltage of the power high supply VDD.
Additionally, the protection device 40 further includes a second diode protection structure 22 associated with a base-emitter junction of the first NPN bipolar transistor 51, which can correspond to a junction between the left region of the p-well 42 and the first N+ region 45a of FIGS. 2A-2C. The second diode protection structure 22 can be used to protect the IC against transient electrical events that cause the voltage of the signal pin 2 to decrease relative to the voltage of the power low supply VSS. Furthermore, the protection device 40 further includes a second thyristor protection structure 12 associated with the third NPN bipolar transistor 53 and the second PNP bipolar transistor 62, which are cross-coupled. The second thyristor protection structure 12 can correspond to the PNPN structure of the sixth P+ region 44f, the second n-well 43b, the central region of the p-well 42, and the fourth N+ region 45d. The second thyristor protection structure 12 can be used to protect the IC against transient electrical events that cause the voltage of the signal pin 2 to increase relative to the voltage of the power low supply VSS.
With continuing reference to FIGS. 2A-3, the protection device 40 further includes an integrated supply clamp that includes a third thyristor protection structure 13 and a third diode protection structure 23. The third thyristor protection structure 13 is associated with the second NPN bipolar transistor 52 and the first PNP bipolar transistor 61, which are cross-coupled. The third thyristor protection structure 13 can correspond to the PNPN structure of the second P+ region 44b, the first n-well 43a, the central region of the p-well 42, and the fourth N+ region 45d. The third thyristor protection structure 13 can be used to protect the IC from transient electrical events that increase the voltage of the power high supply VDD relative to the voltage of the power low supply VSS. The third diode protection structure 23 can be associated with the first diode 63, which can correspond to a junction between the left region of the p-well 42 and the first n-well 43a and with a junction between the right region of the p-well 42 and the second n-well 43b. The third diode protection structure 23 can be used to protect the IC from transient electrical events that decrease the voltage of the power high supply VDD relative to the voltage of the power low supply VSS.
As shown in FIGS. 2A-2C, the third thyristor protection structure 13 and the third diode protection structure 23 share a portion of the wells and diffusion regions associated with the first and second thyristor protection structures 11, 12. Accordingly, the protection device can be implemented in a fraction of the footprint or area relative to a protection scheme using a supply clamp implemented using a separate layout.
As described above, the first and second diode protection structures 21, 22 are formed from the base-emitter junctions of the second PNP bipolar transistor 62 and the first NPN bipolar transistor 51, respectively. The base-emitter junctions can have a relatively low capacitance relative to certain other diode structures, and thus can have a relatively small impact on the speed and/or signal integrity of signals transmitted or received on the signal pin 2.
With continued reference to FIGS. 2A-3, the protection device 40 further includes a fourth diode protection structure 24 associated with the second diode 64, which can correspond to a junction between the left region of the p-well 42 and the first n-well 43a and with a junction between the right region of the p-well 42 and the second n-well 43b. The fourth diode protection structure 24 can help protect the p-well 42 from damage during a transient electrical event. In the illustrated configuration, the anode of the second diode 64 is electrically connected to the substrate voltage VSUB. However, other configurations are possible. For example, in one embodiment the substrate voltage VSUB is omitted in favor of connecting the anode of the second diode 64 to the power low supply VSS. In such a configuration, the fourth diode protection structure 24 can operate in parallel with the third diode protection structure 23, thereby increasing the protection device's current handling capability for ESD events that increase the voltage of the power low supply VSS relative to the voltage of the power high supply VDD.
FIG. 4A is a top plan view of a protection device 70 according to another embodiment. FIG. 4B is a cross section of the protection device 70 of FIG. 4A taken along the lines 4B-4B.
The protection device 70 of FIGS. 4A-4B is similar to the protection device 40 of FIGS. 2A-2C, except that the protection device 70 of FIGS. 4A-4B illustrates a configuration in which the fifth P+ region 44e and fifth N+ region 45e have been omitted. Additionally, the sixth to eighth gate regions 46f-46h have been omitted in favor of using a gate region 71, which extends over the p-well 42 and the second n-well 43b between the fourth N+ region 45d and the sixth P+ region 44f As shown in FIG. 4B, the gate region 71 is electrically connected to the power low supply VSS.
FIG. 4B has been annotated to include the p-type field-effect transistor (PFET) 72. The PFET 72 includes a gate associated with the gate region 71, a source associated with the sixth P+ region 44f, a drain associated with the central region of the p-well 42, and a body associated with the second n-well 43b. 
The PFET 72 can enhance the protection against stress conditions between the signal pin 2 and the power low supply VSS. For example, when an ESD event causes the voltage of the signal pin 2 to increase relative to the voltage of the power low supply VSS, the PFET 72 can activate and provide current into the base of a corresponding bipolar transistor, thereby improving ESD performance. Additionally, the parasitic gate-to-source capacitance of the PFET 72 can aid in providing a displacement current or C*dV/dt current that can expedite or speed-up the activation of the protection device 70 when an ESD event causes the voltage of the power low supply VSS to change with time. Thus, including the gate region 71 can substantially expedite the protection device's response during a stress condition. Although including the gate region 71 can enhance the protection device's on-state performance, including the gate region 71 can also increase the protection device's off-state power consumption, since the PFET 72 can have an associated leakage current. In certain implementations, the PFET 72 is configured as a high threshold voltage device so as to reduce off-state conduction between the signal pin 2 and the power high supply VDD and to prevent the PFET 72 from interfering from signals received or transmitted on the signal pin 2. Additional details of the protection device 70 can be similar to those described earlier with respect to FIGS. 2A-3.
Persons having ordinary skill in the art will appreciate that one or more of the protection devices 40 of FIGS. 2A-2C and/or one or more of the protection devices 70 of FIGS. 4A-4B can be used to provide protection to the pins of an integrated circuit. For example, in certain implementations, the protection device 70 of FIGS. 3A-3B is used to protect a first signal pin associated with a first power supply domain, and the protection device 40 of FIGS. 2A-2C is used to protect a second signal pin associated with a second power supply domain that has a higher voltage than the first power supply domain. For example, in one embodiment, the protection device 70 of FIGS. 3A-3B is used to protect a 0.9 V signal pin and the protection device 40 of FIGS. 2A-2C is used to protect a 1.8 V signal pin. However, other configurations are possible.
FIG. 4C is a circuit diagram 75 of the protection device 70 of FIGS. 4A-4B. The circuit diagram 75 of FIG. 4C is similar to the circuit diagram 50 of FIG. 3, except that the circuit diagram 75 of FIG. 4C further includes the PFET transistor 72. As shown in FIG. 4C, the PFET transistor 72 includes a gate electrically connected to the power low supply VSS, a drain electrically connected to the base of the third NPN bipolar transistor 53, a source electrically connected to the signal pin 2, and a body electrically connected to the power high supply VDD. During a transient electrical event between the signal pin 2 and power low supply VSS, the PFET transistor 72 can turn-on and provide a current into the base of the third NPN bipolar transistor 53, thereby expediting activation of the second thyristor protection structure 12. In certain implementations, the PFET 72 is configured as a high threshold voltage device so as to reduce off-state conduction between the signal pin 2 and the power high supply VDD and to prevent the PFET 72 from interfering from signals received or transmitted on the signal pin 2. For example, as will be described below with reference to FIG. 12, the PFET 72 can be configured to have a high threshold voltage by implementing the gate of the PFET 72 using n-metal. However, other configurations for achieving high threshold voltage are possible, such as use of selective high k dielectric, thicker oxide formation, and/or selective channel doping. Additional details of the circuit diagram 75 can be as described earlier.
FIG. 5 is a cross section of a protection device 80 according to another embodiment. The protection device 80 of FIG. 5 is similar to the protection device 40 of FIGS. 2A-2C, except that the protection device 80 illustrates a configuration in which the second N+ region 45b is electrically floating, rather than electrically connected to the power high supply VDD. Configuring the protection device 80 in this manner provides a breakdown voltage collector-emitter open (BVCEO) characteristic between the power high supply VDD and the signal pin 2, which can lower the protection device's trigger voltage for an ESD event received between the power high supply VDD and the signal pin 2 relative to the configuration shown in FIGS. 2A-2C.
Additionally, the protection device 80 of FIG. 5 can have reduced MOS-induced leakage relative to the protection device 40 of FIGS. 2A-2C. For example, the protection device 80 can include an NFET transistor having a gate associated with the second gate region 46b, a source associated with the first N+ region 45a, a drain associated with the first n-well 43a, and a body associated with the left region of the p-well 42. Configuring the second N+ region 45b to be electrically floating can reduce leakage between the power high supply VDD and the signal pin 2 through the NFET transistor, since the connection between the NFET's drain and the power high supply VDD can be disconnected.
Persons having ordinary skill in the art will appreciate that any of the protection devices described herein can be configured with the second N+ region 45b electrically floating so as to reduce the protection device's trigger voltage. Indeed, implementing the protection devices described herein with a BVCEO characteristic is one of many possible device variations suitable for providing fine-tune adjustment of the protection device's characteristics so as to provide protection suitable for a particular application and/or fabrication process.
FIG. 6 is a cross section of a protection device 90 according to another embodiment. The protection device 90 of FIG. 6 is similar to the protection device 70 of FIGS. 4A-4B, except that the protection device 90 illustrates a configuration in which the second N+ region 45b is electrically floating, rather than electrically connected to the power high supply VDD. Configuring the protection device 90 in this manner provides a BVCEO characteristic between the power high supply VDD and the signal pin 2. Additionally, the protection device 90 of FIG. 6 can have reduced MOS-induced leakage relative to the protection device 70 of FIGS. 4A-4B. For example, the protection device 90 can have reduced leakage between the power high supply VDD and the signal pin 2, since an NFET transistor associated with the second gate region 46b can have a drain that is disconnected from the power high supply VDD. Additional details of the protection device 90 can be similar to those described earlier.
FIG. 7 is a cross section of a protection device 100 according to another embodiment. The protection device 100 of FIG. 7 is similar to the protection device 40 of FIGS. 2A-2C, except that the protection device 100 further includes a first resist protective oxide (RPO) region 81a and a second RPO region 81b. In the illustrated configuration, the first RPO region 81a is disposed over the third N+ region 45c, over the fourth gate region 46d, over the fourth P+ region 44d, and over a portion of the third and fifth gate regions 46c, 46e. Additionally, the second RPO region 81b is disposed over the fifth P+ region 44e, over the seventh gate region 46g, over the fifth N+ region 45e, and over a portion of the sixth and eighth gate regions 46f, 46h. However, other configurations of the first and second RPO regions 81a, 81b are possible and/or implementations in which the first or second RPO regions 81a, 81b are omitted.
The first and second RPO regions 81a, 81b can be used to prevent local formation of a silicide layer on a surface of the protection device 100 during processing. A silicide layer can have a relatively low resistance, and thus can have a high current density during an ESD event. In certain instances, blocking the silicide formation can further enhance high stress current handling capability, as high currents through the silicide layer and/or close to the semiconductor surface can lead to device damage, such as silicide melting associated with Joule heating and lower melting point of the silicide formation. Accordingly, using the first and second RPO regions 81a, 81b to prevent formation of a silicide layer (while silicide is formed on other contact regions) can increase the protection device's robustness during overstress by relatively increasing an amount of current that flows through the protection device's deeper semiconductor regions, such as the protection device's wells and diffusion regions, compared to the absence of the RPO regions.
FIG. 8 is a cross section of a protection device 110 according to another embodiment. The protection device 110 of FIG. 8 is similar to the protection device 70 of FIGS. 4A-4B, except that the protection device 110 further includes the first RPO region 81a. Additional details of the protection device 110 can be similar to those described earlier.
FIG. 9 is a cross section of a protection device 120 according to another embodiment. The protection device 120 of FIG. 9 is similar to the protection device 100 of FIG. 7, except that the protection device 120 illustrates a configuration in which the fifth and sixth gate regions 46e, 46f are omitted in favor of including oxide regions 48 both between the fourth N+ region 45d and the fourth P+ region 44d and between the fourth N+ region 45d and the fifth P+ region 44e. Inclusion of the oxide regions 48 in this configuration can reduce the protection device's leakage current between the power high supply VDD and the power low supply VSS and increase overvoltage trigger. For example, the oxide regions 48 can decrease the leakage current between the fourth N+ region 45d and the fourth and fifth P+ regions 44d, 44e. Additionally, including the oxide regions 48 in this configuration can increase field constraints for breakdown between the fourth N+ region 45d and the power high supply VDD (via the third P+ region 44c or the second N+ region 45b) and/or between the fourth N+ region 45d and the signal pin 2 (via the sixth P+ region 44f). Additional details of the protection device 120 can be similar to those described earlier.
Although the configuration of oxide regions 48 shown in FIG. 9 is illustrated in combination with the first and second RPO regions 81a, 81b, the oxide regions 48 can be implemented in this manner in implementations in which the first and/or second RPO regions 81a, 81b are omitted or arranged in other ways. Indeed, the variations of protection devices described herein can be selectively combined to provide further protection device configurations suitable for a particular application or fabrication process. Thus, certain features shown in the context of one protection device can be incorporated into other protection devices as well.
FIG. 10 is a cross section of a protection device 130 according to another embodiment. The protection device 130 of FIG. 10 is similar to the protection device 110 of FIG. 8, except that the protection device 130 illustrates a configuration in which the fifth gate region 46e is omitted in favor of including the oxide region 48 between the fourth N+ region 45d and the fourth P+ region 44d. Configuring the protection device 130 in this manner can reduce the protection device's leakage current between the power high supply VDD and the power low supply VSS and increase overvoltage trigger. Additionally, the oxide region 48 can increase field constraints for breakdown between the fourth N+ region 45d and the power high supply VDD via the third P+ region 44c or the second N+ region 45b. Additional details of the protection device 130 can be similar to those described earlier.
FIG. 11A is an annotated cross section of a protection device 140 according to another embodiment. The protection device 140 of FIG. 11A is similar to the protection device 100 of FIG. 7, except that FIG. 11A illustrates an implementation in which the first to ninth gate regions 46a-46i of FIG. 7 have been implemented using the first to ninth p-metal gates 146a-146i, respectively.
In certain processes, such as high-k metal gate CMOS processes, metals can be used to implement the gates of NFET and PFET transistors. Additionally, the composition and/or processing of the gate metal of PFET transistors and the gate metal of NFET transistors can be separately configured to achieve work functions corresponding to suitable threshold voltages for NFET and PFET transistors. As used herein, p-metal (PM) can correspond to a gate metal structure associated with the process's PFET transistors and n-metal (NM) can correspond to a gate metal structure associated with the process's NFET transistors.
The protection device 140 has been annotated to include various devices described earlier with reference to FIG. 2A, such as the first to third NPN bipolar transistors 51-53, the first to third resistors 57-59, the first and second PNP bipolar transistors 61, 62, and the first and second diodes 63, 64. Additionally, the protection device 140 has been annotated to include a first NFET transistor 141 and a first PFET transistor 142. The first NFET transistor 141 includes a gate associated with the second p-metal gate region 146b, a source associated with the first N+ region 45a, a drain associated with the first n-well 43a, and a body associated with the left region of the p-well 42. Additionally, the first PFET transistor 142 includes a gate associated with the second p-metal gate region 146b, a source associated with the second P+ region 44b, a drain associated with the left region of the p-well 42, and a body associated with the first n-well 43a. 
In the configuration shown in FIG. 11A, p-metal has been used to implement the second p-metal gate region 146b, which can increase the threshold voltage of the first NFET transistor 141 and provide lower standing leakage and help ensure that the first NFET transistor 141 does not activate during normal operating conditions of the signal pin 2. Although FIG. 7 illustrates one suitable configuration for increasing the threshold voltage of the first NFET transistor 141, other configurations are possible. For example, the NFET's threshold voltage can be increased by use of selective high k dielectric, thicker oxide formation, and/or selective channel doping.
FIG. 11B is a circuit diagram 145 of the protection device 140 of FIG. 11A. The circuit diagram 145 of FIG. 11B is similar to the circuit diagram 50 of FIG. 3, except that the circuit diagram 145 of FIG. 11B further includes the first NFET transistor 141 and the first PFET transistor 142. As shown in FIG. 11B, the first NFET transistor 141 includes a source electrically connected to the signal pin 2, a body electrically connected to the power low supply VSS, and a gate and drain electrically connected to the power high supply VDD. Additionally, the first PFET transistor 142 includes a drain electrically connected to the power low supply VSS, and a gate, source, and body electrically connected to the power high supply VDD.
In certain implementations, the first NFET 141 is configured as a high threshold voltage device so as to reduce off-state conduction between the signal pin 2 and the power high supply VDD and to prevent the first NFET 141 from interfering from signals received or transmitted on the signal pin 2. Additional details of the circuit diagram 145 can be as described earlier.
FIG. 12 is a cross section of a protection device 150 according to another embodiment. The protection device 150 of FIG. 12 is similar to the protection device 110 of FIG. 8, except that the protection device 150 of FIG. 12 implements the gate regions 46a-46e, 46i of FIG. 8 using p-metal gates 146a-146e, 146i, respectively, and implements the gate region 71 of FIG. 8 using an n-metal gate 147.
In a manner similar to that described earlier with reference to FIG. 11A, the p-metal gate 146b can increase the threshold voltage of the NFET transistor 141 of FIG. 11A. Additionally, the n-metal gate 147 can increase the threshold voltage of the PFET transistor 72 relative to a configuration using p-metal, and thus can help to further reduce the protection device's leakage current. Although using n-metal to implement the gates of PFETs and using p-metal to implement the gates of NFETs is one suitable method of increasing threshold voltage, other methods are possible. For example, an NFET's or PFET's threshold voltage can be increased by defining thicker gate regions, selective higher k dielectric formations, increasing channel length, and/or incorporating selective doping implants for threshold voltage control underneath the channel. Additional details of the protection device 150 can be similar to those described earlier.
FIG. 13A is a cross section of a protection device 160 according to another embodiment. The protection device 160 of FIG. 13A is similar to the protection device 100 of FIG. 7, except that the protection device 160 further includes a ninth P+region 44i positioned between the first N+ region 45a and the second gate region 46b. Additionally, a third RPO region 81c has been disposed over the ninth P+ region 44i, a portion of the first N+ region 45a, a portion of the second gate region 46b, and a portion of the p-well 42 between the first N+ region 45a and the ninth P+ region 44i. 
The ninth P+ region 44i can aid in preventing the formation of the first NFET transistor 141 shown in FIG. 11A. Preventing the formation of the first NFET transistor 141 can be desirable in certain configurations, such as very low leakage applications and/or implementations in which a voltage difference between the power high and power low supplies VDD, VSS is relatively large. Additionally, preventing the first NFET transistor's formation can be desirable when the threshold voltage of the first NFET transistor 141 is relatively low, including, for example, in configurations in which a protection device is fabricated using a manufacturing process in which p-metal is unavailable to increase the threshold voltage of the first NFET transistor 141. Additional details of the protection device 160 can be similar to those described earlier.
In the illustrated configuration, the first N+ region 45a and the ninth P+ region 44i are separated by a distance d1, which can be used to control a punch-through induced breakdown voltage of the junction. In one embodiment, the distance d1 is selected to be in the range of about 0.12 μm to about 0.6 μm, for instance 0.2 μm. However, other distances are possible, including, for example, distances that depending on system-level and/or processing constraints.
FIG. 13B is a cross section of a protection device 165 according to another embodiment. The protection device 165 of FIG. 13B is similar to the protection device 160 of FIG. 13A, except that the protection device 165 omits the ninth P+ region 44i. Additionally, the first N+ region 45a has been implemented such that the first N+ region 45a is spaced apart from the second gate region 46b and such that the first N+ region 45a does not extend beneath the third RPO region 81c. 
Configuring the first N+ region 45a in this manner can increase the first N+ region's breakdown voltage relative to the configuration shown in FIG. 13A. For example, in certain processes, the protection device 160 of FIG. 13A can have a relatively low breakdown voltage between the first N+ region 45a and the ninth P+ region 44i, since such regions can be relatively highly doped. Additional details of the protection device 165 can be similar to those described earlier.
FIG. 14A is a cross section of a protection device 170 according to another embodiment. The protection device 170 of FIG. 14A is similar to the protection device 110 of FIG. 8, except that the protection device 170 further includes the ninth P+ region 44i and the third RPO region 81c, which can be as described earlier. Additionally, the protection device 170 further includes a seventh N+ region 45g and a fourth a RPO region 81d. The seventh N+ region 45g is positioned between the sixth P+ region 44f and the gate region 71. The fourth RPO region 81d is disposed over the seventh N+ region 45g, a portion of the gate region 71, and a portion of the sixth P+ region 44f, and a portion of the second n-well 43b between the seventh N+ region 45g and the sixth P+ region 44f. 
The seventh N+ region 45g can prevent the formation of the PFET transistor 72 shown in FIG. 4B, which can be desirable in certain configurations, such as low leakage configurations. In the illustrated configuration, the seventh N+ region 45g and the sixth P+ region 44f are separated by a distance d2, which can be selected to control a punch-through induced breakdown voltage of the junction. In one embodiment, the distance d2 is selected to be in the range of about 0.12 μm to about 0.6 μm, for instance 0.2 μm. However, other distances are possible, including, for example, distances that depending on system-level and/or processing constraints. Additional details of the protection device 170 can be similar to those described earlier.
FIG. 14B is a cross section of a protection device 175 according to another embodiment. The protection device 175 of FIG. 14B is similar to the protection device 170 of FIG. 14A, except that the protection device 175 omits the ninth P+ region 44i and the seventh N+ region 45g. Additionally, the first N+ region 45a has been implemented such that the first N+ region 45a is spaced apart from the second gate region 46b and such that the first N+ region 45a does not extend beneath the third RPO region 81c. Furthermore, the sixth P+ region 44f has been implemented such that the sixth P+ region 44f is spaced apart from the gate region 71 and such that the sixth P+ region 44f does not extend beneath the fourth RPO region 81d. 
Configuring the first N+ region 45a in this manner can increase the first N+ region's breakdown voltage relative to the configuration shown in FIG. 14A and avoid NMOS formation to reduce standing leakage. For example, the gate region 46b of FIG. 14B does not include n-type regions on opposing sides of the gate region 46b, and thus does not include an associated NMOS transistor. Preventing the formation of the NMOS transistor can be useful in a variety of configurations, such as very low standing IO leakage implementations and/or configurations using manufacturing processes in which a high threshold voltage option for the NMOS transistor is limited or unavailable.
Additionally, configuring the sixth P+ region 44f in this manner can increase the sixth P+ region's breakdown voltage relative to the configuration shown in FIG. 14A and avoid PMOS formation to reduce standing leakage. For example, the gate region 71 of FIG. 14B does not include p-type regions on opposing sides of the gate region 71, and thus does not include an associated PMOS transistor. Preventing the formation of the PMOS transistor can be useful in a variety of configurations, such as very low standing IO leakage implementations and/or configurations using manufacturing processes in which a high threshold voltage option for the PMOS transistor is limited or unavailable. Additional details of the protection device 175 can be similar to those described earlier.
FIG. 15 is a cross section of a protection device 180 according to another embodiment. The protection device 180 of FIG. 15 is similar to the protection device 160 of FIG. 13A, except that the protection device 180 further includes an oxide region 48 positioned between the first N+ region 45a and the ninth P+ region 44i. Configuring the protection device 180 in this manner can reduce the protection device's off-state power consumption by reducing the flow of leakage current between the first N+ region 45a and the ninth P+ region 44i. Additional details of the protection device 180 can be similar to those described earlier.
FIG. 16 is a cross section of a protection device 190 according to another embodiment. The protection device 190 of FIG. 16 is similar to the protection device 170 of FIG. 14A, except that the protection device 190 further includes oxide regions 48 positioned between the first N+ region 45a and the ninth P+ region 44i and between the seventh N+ region 45g and the sixth P+ region 44f Configuring the protection device 190 in this manner can reduce the protection device's leakage current. Additional details of the protection device 190 can be similar to those described earlier.
FIG. 17 is a cross section of a protection device 200 according to another embodiment. The protection device 200 of FIG. 17 is similar to the protection device 40 of FIGS. 2A-2C, except that the protection device 200 illustrates a configuration in which the second gate region 46b is omitted in favor of including an oxide region 48 between the first N+ region 45a and the second P+ region 44b. 
Including the oxide region 48 between the first N+ region 45a and the second P+ region 44b can prevent the formation of the first NFET transistor 141 and the first PFET transistor 142 shown in FIG. 11A, which can be desirable in certain configurations, such as low leakage configurations at higher operating voltage conditions. Additional details of the protection device 200 can be similar to those described earlier.
FIG. 18 is a cross section of a protection device 210 according to another embodiment. The protection device 210 of FIG. 18 is similar to the protection device 70 of FIGS. 4A-4B, except that the protection device 200 illustrates a configuration in which both the gate region 46b and the gate region 71 are omitted in favor of including oxide regions 48 between the first N+ region 45a and the second P+ region 44b and between the fourth N+ region 45d and the sixth P+ region 44f. 
Including the oxide region 48 between the first N+ region 45a and the second P+ region 44b can prevent the formation of the first NFET transistor 141 and the first PFET transistor 142 shown in FIG. 11A. Additionally, including the oxide region 48 between the fourth N+ region 45d and the sixth P+ region 44f can prevent the formation of the PFET transistor 72 of FIG. 4B. Additional details of the protection device 210 can be similar to those described earlier.
FIG. 19 is a cross section of a protection device 300 according to another embodiment. The protection device 300 includes an n-well 343, first to third p-wells 342a-342c, first to eighth N+ regions 345a-345h, first to seventh P+ regions 344a-344g, first to ninth gate regions 46a-46i, first and second RPO regions 81a, 81b, and a deep n-well 347. The protection device 300 is fabricated in the p-type substrate 49.
The protection device 300 of FIG. 19 is similar to the protection device 100 of FIG. 7, except that the doping of the wells and diffusion regions has been reversed so as to provide a protection device of a complementary polarity. For example, the n-well 343 of FIG. 19 can correspond to the p-well 42 of FIG. 7 but with polarity reversed, and the first and second p-wells 342a, 342b of FIG. 19 can correspond to the first and second n-wells 43a, 43b of FIG. 7, respectively, but with polarity reversed. Similarly, the first to eighth N+ regions 345a-345h of FIG. 19 can correspond to the first to eighth P+regions 44a-44h of FIG. 7, respectively, but with polarity reversed. Likewise, the first to sixth P+ regions 344a-344f of FIG. 19 can correspond to the first to sixth N+ regions 45a-45f of FIG. 7, respectively, but with polarity reversed.
Relative to the protection device 100 of FIG. 7, the protection device 300 of FIG. 19 further includes the seventh P+ region 344g, the third p-well 342c, and the deep n-well 347. The seventh P+ region 344g and the third p-well 342c can be configured to surround a perimeter of the protection device 300, and can operate as a guard ring to reduce carrier injection into the p-type substrate 49 during an ESD event. The deep n-well 347 has been positioned beneath the n-well 343 and the first and second p-wells 342a, 342b, and can be used to electrically isolate the first and second p-wells 342a, 342b from the p-type substrate 49. Additional details of the protection device 300 can be similar to those described earlier.
To maintain proper junction biasing, the electrical connections between the protection device 300 of FIG. 19 and the power high and low supplies VDD, VSS has been reversed relative to the configuration of FIG. 7. For example, as shown in FIG. 19, the second gate region 46b, the second N+ region 345b, the second P+ region 344b, the third N+ region 345c, and the sixth P+ region 344f are electrically connected to the power low supply VSS. Additionally, the first N+ region 345a, the fourth P+ region 344d, and the seventh N+ region 345g are electrically connected to the power high supply VDD. Furthermore, the eighth N+ region 345h is electrically connected to an n-well supply VNW, which can be Kelvin-connected to a power high supply pin in certain configurations. The first P+ region 344a and the sixth N+ region 345f are electrically connected to the signal pin 2, and the seventh P+ region 344g is electrically connected to the substrate supply VSUB. The first gate region 46a and the third to ninth gate regions 46c-46i are electrically floating.
Although FIG. 19 illustrates a complementary configuration of the protection device 100 of FIG. 7, any of the protection devices described herein can be implemented in a complementary configuration including the DNW as described in FIG. 19.
FIG. 20 is a cross section of a protection device 310 according to another embodiment.
The protection device 310 of FIG. 20 is similar to the protection device 300 of FIG. 19, except that the protection device 310 of FIG. 20 illustrates a configuration in which the fifth N+ region 345e and fifth P+ region 344e have been omitted. Additionally, the sixth to eighth gate regions 46f-46h have been omitted in favor of using the gate region 71, which extends over the n-well 343 and the second p-well 342b between the fourth P+ region 344d and the sixth N+ region 345f. As shown in FIG. 20, the gate region 71 is electrically connected to the power high supply VDD.
The protection device 310 of FIG. 20 illustrates a complementary implementation of the protection device 110 of FIG. 8. Additional details of the protection device 310 can be similar to those described earlier.
Applications
Devices employing the above described schemes can be implemented into various high performance electronic devices and interface applications operating in harsh electrical environments. Examples of the electronic devices can include, but are not limited to, consumer electronic products, parts of the consumer electronic products, electronic test equipment, high robustness industrial and automotive applications, etc. Examples of the electronic devices can also include circuits of optical networks or other communication networks. The consumer electronic products can include, but are not limited to, an automobile, an engine control unit, a vehicle engine management controller, a transmission controller, a seatbelt controller, an anti-lock brake system controller, a camcorder, a camera, a digital camera, a portable memory chip, a washer, a dryer, a washer/dryer, a copier, a facsimile machine, a scanner, a multi functional peripheral device, etc. Further, the electronic device can include unfinished products, including those for industrial, medical and automotive applications.
The foregoing description and claims may refer to elements or features as being “connected” or “coupled” together. As used herein, unless expressly stated otherwise, “connected” means that one element/feature is directly or indirectly connected to another element/feature, and not necessarily mechanically. Likewise, unless expressly stated otherwise, “coupled” means that one element/feature is directly or indirectly coupled to another element/feature, and not necessarily mechanically. Thus, although the various schematics shown in the figures depict example arrangements of elements and components, additional intervening elements, devices, features, or components may be present in an actual embodiment (assuming that the functionality of the depicted circuits is not adversely affected).
Although this invention has been described in terms of certain embodiments, other embodiments that are apparent to those of ordinary skill in the art, including embodiments that do not provide all of the features and advantages set forth herein, are also within the scope of this invention. Moreover, the various embodiments described above can be combined to provide further embodiments. In addition, certain features shown in the context of one embodiment can be incorporated into other embodiments as well. Accordingly, the scope of the present invention is defined only by reference to the appended claims.

## Claims

1. An integrated circuit comprising:
a power high pin configured to receive a first supply voltage;
a power low pin configured to receive a second supply voltage;
a signal pin configured to receive a signal;
a first NPN bipolar transistor including an emitter electrically connected to the signal pin;
a first PNP bipolar transistor including an emitter electrically connected to the power high pin, wherein the first PNP bipolar transistor and the first NPN bipolar transistor are cross-coupled and configured to operate as a first thyristor protection structure between the power high pin and the signal pin;
a second NPN bipolar transistor including an emitter electrically connected to the power low pin;
a third NPN bipolar transistor including an emitter electrically connected to the power low pin;
a second PNP bipolar transistor including an emitter electrically connected to the signal pin, wherein the second PNP bipolar transistor and the third NPN bipolar transistor are cross-coupled and configured to operate as a second thyristor protection structure between the signal pin and the power low pin,
wherein the first PNP bipolar transistor and the second NPN bipolar transistor are cross-coupled and configured operate as a third thyristor protection structure between the power high pin and the power low pin.

2. The integrated circuit of claim 1, wherein a base-emitter junction of the second PNP bipolar transistor is configured to operate as a first diode protection structure between the signal pin and the power high pin, and wherein a base-emitter junction of the first NPN bipolar transistor is configured to operate as a second diode protection structure between the power low pin and the signal pin.

3. The integrated circuit of claim 2, further comprising a third diode protection structure electrically connected between the power high pin and the power low pin.

4. The integrated circuit of claim 3,
wherein the first thyristor protection structure is configured to switch from a high impedance off-state to a low impedance on-state to protect the integrated circuit when a voltage of the power high pin increases during voltage overstress relative to a voltage of the signal pin,
wherein the first diode protection structure is configured to provide a low impedance current path and protect the integrated circuit when the voltage of the power high pin decreases relative to the voltage of the signal pin,
wherein the second thyristor protection structure is configured to switch from a high impedance off-state to a low impedance on-state to protect the integrated circuit when the voltage of the signal pin increases relative to a voltage of the power low pin,
wherein the second diode protection structure is configured to provide a low impedance current path and protect the integrated circuit when the voltage of the signal pin decreases relative to the voltage of the power low pin,
wherein the third thyristor protection structure is configured to switch from a high impedance off-state to a low impedance on-state to protect the integrated circuit when a voltage of the power high pin increases relative to a voltage of the power low pin, and
wherein the third diode protection structure is configured to provide a low impedance current path and protect the integrated circuit when a voltage of the power high pin decreases relative to a voltage of the power low pin.

5. The integrated circuit of claim 3, further comprising:
a p-type field-effect transistor (PFET) including a gate electrically connected to the power low pin, a drain electrically connected to a base of the third NPN bipolar transistor, a source electrically connected to the signal pin and a body electrically connected to the power high pin, wherein the PFET is configured to turn-on and provide a current into the base of the third NPN bipolar transistor when the voltage of the signal pin increases relative to a voltage of the power low pin.

6. The integrated circuit of claim 5, further comprising:
a first metal oxide semiconductor transistor and a second metal oxide semiconductor transistor, wherein the first metal oxide semiconductor transistor has a p-type channel and a first type of gate metal structure, wherein the second metal oxide semiconductor transistor has an n-type channel and a second type of gate metal structure different from the first type of gate metal structure,
wherein the gate of the PFET comprises the second type of metal gate structure to define a high threshold voltage PMOS.

7. The integrated circuit of claim 3, further comprising a first resistor electrically connected between a base of the third NPN bipolar transistor and the emitter of the third NPN bipolar transistor.

8. The integrated circuit of claim 7, further comprising a second resistor electrically connected between a base of the second NPN bipolar transistor and a base of the first NPN bipolar transistor.

9. The integrated circuit of claim 8, further comprising a third resistor electrically connected between an emitter of the first PNP bipolar transistor and a base of the first PNP bipolar transistor.

10. The integrated circuit of claim 3, wherein a resistor is not electrically connected between the emitter of the first PNP bipolar transistor and a base of the first PNP bipolar transistor so as to configure the first PNP bipolar transistor with a breakdown voltage collector emitter open (BVCEQ) characteristic, wherein the first thyristor protection structure is configured to have a breakdown voltage controlled by the BVCEO characteristic.

11. The integrated circuit of claim 3, further comprising a fourth diode protection structure electrically connected between the power high pin and a substrate supply pin.

12. The integrated circuit of claim 11, wherein an anode of the fourth diode protection structure includes a p-type active region configured to operate as a latch-up guard ring.

13. The integrated circuit of claim 3, further comprising a fourth diode protection structure electrically connected between the power high pin and the power low pin.

14. The integrated circuit of claim 3, further comprising:
an n-type field-effect (NFET) transistor including a gate electrically connected to the power high pin, a drain electrically connected to the power high pin, a source electrically connected to the signal pin, and a body electrically connected to the power low pin; and
a p-type field-effect (PFET) transistor including a gate electrically connected to the power high pin, a drain electrically connected to the power low pin, a source electrically connected to the power high pin, and a body electrically connected to the power high pin.

15. The integrated circuit of claim 14, further comprising:
a first metal oxide semiconductor transistor and a second metal oxide semiconductor transistor, wherein the first metal oxide semiconductor transistor has a p-type channel and a first type of gate metal structure, wherein the second metal oxide semiconductor transistor has an n-type channel and a second type of gate metal structure different from the first type of gate metal structure,
wherein the gate of the NFET comprises the first type of metal gate structure to define a high threshold voltage NMOS.

16. A method of forming an integrated circuit, the method comprising:
providing a first thyristor structure between a power high pin and a signal pin, wherein the first thyristor structure is associated with a first NPN bipolar transistor and a first PNP bipolar transistor, wherein the first NPN bipolar transistor and the first PNP bipolar transistor are cross-coupled;
providing a second thyristor structure between the power high pin and the power low pin, wherein the second thyristor structure is associated with a second NPN bipolar transistor and the first PNP bipolar transistor, wherein the second NPN bipolar transistor and the first PNP bipolar transistor are cross-coupled;
providing a third thyristor structure between the signal pin and a power low pin, wherein the third thyristor structure is associated with a third NPN bipolar transistor and a second PNP bipolar transistor, wherein the third NPN bipolar transistor and the second PNP bipolar transistor are cross-coupled.

17. The method of claim 16, further comprising surrounding the first thyristor protection structure, the second thyristor protection structure, and the third thyristor protection structure using a common substrate guard ring.

18. The method of claim 16, further comprising:
providing a first diode protection structure between the power high pin and the signal pin, the first diode protection structure associated with a base-emitter junction of the second PNP bipolar transistor; and
providing a second diode protection structure between the power low pin and the signal pin, the second diode protection structure associated with a base-emitter junction of the first NPN bipolar transistor.

19. The method of claim 18, further comprising:
providing a p-type field-effect (PFET) transistor including a gate electrically connected to the power low pin, a drain electrically connected to a base of the third NPN bipolar transistor, a source electrically connected to the signal pin, and a body electrically connected to the power high pin.

20. The method of claim 19, further comprising:
forming a first metal oxide semiconductor transistor and a second metal oxide semiconductor transistor, wherein the first metal oxide semiconductor transistor has a p-type channel and a first type of gate metal structure, wherein the second metal oxide semiconductor transistor has an n-type channel and a second type of gate metal structure different from the first type of gate metal structure; and
implementing the gate of the PFET using the second type of gate metal structure to define a high threshold voltage PMOS.

21. The method of claim 18, further comprising not providing a resistor between an emitter and a base of the first PNP bipolar transistor so as to configure the first PNP bipolar transistor with a breakdown voltage collector emitter open (BVCEO) characteristic, wherein the first thyristor protection structure is configured to have a breakdown voltage controlled by the BVCEO characteristic.

22. The method of claim 18, further comprising:
providing an n-type field-effect (NFET) transistor including a gate electrically connected to the power high pin, a drain electrically connected to the power high pin, a source electrically connected to the signal pin, and a body electrically connected to the power low pin; and
providing a p-type field-effect (PFET) transistor including a gate electrically connected to the power high pin, a drain electrically connected to the power low pin, a source electrically connected to the power high pin, and a body electrically connected to the power high pin.

23. The method of claim 22, further comprising:
forming a first metal oxide semiconductor transistor and a second metal oxide semiconductor transistor, wherein the first metal oxide semiconductor transistor has a p-type channel and a first type of gate metal structure, wherein the second metal oxide semiconductor transistor has an n-type channel and a second type of gate metal structure different from the first type of gate metal structure; and
implementing the gate of the NFET using the first type of gate metal structure to define a high threshold voltage NMOS.