Further, if a few simple precautions are taken at the design stage, then latchup can be completely avoided. Latchup has been, and continues to be, a potentially serious cmos reliability concern. The cmos latch schematic is drawn and the triggering methods are discussed. Analog esd and latchup design rule checking and verification. Latchup becomes a real problem when you try to power up and down different sections of your design to save power. By matthew hogan, mentor graphics latchup detection is challenging. Many commercially available advancedtechnology cmos and bipolar integrated circuits are susceptible to singleevent latchup sel effects caused by heavy ions or protons from cosmic rays or solar flares, making them unsuitable for satellite applications. April 1995 single event upset and latchup considerations for cmos devices operated at 3. Mar 21, 2018 sini mukundan march 21, 2018 march 21, 2018 2 comments on cmos latchup latchup is a condition where a low impedance path is created between a supply pin and ground. Latchup is defined as the generation of a lowimpedance path in cmos chips between the power supply v dd and the ground gnd due to the interaction of parasitic pnp and npn bipolar junction transistors bjts. Miyahira jet propulsion laboratory california institute of technology pasadena, california i. Parasitic lateral pnp and vertical npn bjts in a pwell cmos technology. To understand latch up we need to understand the various parasitic components in a cmos.
Every software package contains a full set of examples suitable for that version and are installed with the software. Tong li, chinghan tsai, elyse rosenbaum, sungmo kang, substrate modeling and lumped substrate resistance extraction for cmos esdlatchup circuit simulation, proceedings of the 36th annual acmieee design automation conference, p. Apr 18, 2018 for hv power analog ics, latchup co design methods have significantly evolved from the traditional lv cmos io and core latchup base. The general features of a lumped element latchup model are discussed. Designers can also look forward to the day, in the not too distant future, when even these few simple precautions will no longer be necessary. Request pdf latchup complementary metaloxide semiconductor cmos. It resulted in circuits either malfunctioning or consuming excessive power, and could be either inherent in the. Prior to discussing latchup in cmos devices, it is advantageous to brie. This effect often was observed in earlier generations of cmos circuits. Ker and hsu introduce the phenomenon and basic physical mechanism of latchup, explaining the critical issues that have resurfaced for cmos.
Latchup improvement for tap less library through modified decoupling capacitors cells shailesh kumar, rahul saxena, vikas garg freescale india cmos technology has evolved as the top choice for chip manufacturers. Vlsi design sequential mos logic circuits tutorialspoint. Latchup refers to short circuit formed between power rails in an ic leading to high current and damage to the ic. Latchup is a condition where a low impedance path is created between a supply pin and ground. The modeling of latchup with circuit simulation programs is addressed in this paper. Page 2 of 3 january 19, 2015 by keith sabine the power supply must be able to sustain the supply current drawn while latched the holding current and the supply voltage the holding voltage.
Latch up is basically a positive feedback circuit made up of the paracitic npn and pnp inside your cmos. Transientinduced latchup in cmos integrated circuits wiley. However, when properly applied, cmos devices are quite insensitive to actual conditions that exist in most systems. It resulted in circuits either malfunctioning or consuming excessive power, and could be either inherent in the design or triggered by voltage spikes on io pads that could forward bias pn junctions to which they were connected. Cmos technology has evolved as the top choice for chip manufacturers. A new cad software package for fullchip esd protection circuit verification. In recent years, the latchup is not a problem courtesy to the. Lambdabased designs are scaled to the appropriate absolute units depending on the manufacturing process finally used. Cmos 2 composition the main principle behind cmos circuits that allows them to implement logic gates is the use of ptype and ntype metaloxidesemiconductor fieldeffect transistors to create paths to the output from either the voltage source or.
Throughsoftware sel detection delay measurements of the seltc. The properties of the parasitic bipolar transistors determine the conditions for latchup, and depend on layout and design rules for specific processes. Typical criterion is less than 10% change of all powersupply currents and passing of a full functional test program. Latchup, esd, and other phenomena 5 the parasitic thyristor can be triggered by a rapid rise of the supply voltage. The book all semiconductor device engineers must read to gain a practical feel for latchupinduced failure to produce lowercost and higherdensity chips. Latchup is caused by the triggering of parasitic bipolar structures within an integrated circuit when applying a current or voltage stimulus on. Latch up problem in cmos vlsi design vlsi design latchup is defined as the generation of a lowimpedance path in cmos chips between the power supply v dd and the ground gnd due to the interaction of parasitic pnp and npn bipolar junction transistors bjts. Speaking about cmos transistors, latch up is the phenomenon of low impedance path in cmos between power rail and ground rail due to interaction between parasitic pnp and npn transistors. Overall, latchup design rules, standards, and checker descriptions infrequently explain the reasoning behind their methodological steps in conjunction with real design. Single event upset and latchup considerations for cmos devices operated at 3. Insection iii, a new methodology to extract compact layout rules for latchup prevention is therefore proposed to save chip size 10, 11. Under normal bias, the parasitic scr is in its blocking state but, if subjected to a large voltage spike or if exposed to an ionizing environment, triggering may.
It is possible to design chips to be resistant to latchup by adding a layer of insulating oxide called a trench that surrounds both the nmos and the pmos transistors. Remember that to turn on a npn or a pnp, you just need to have that vbe voltage. May 04, 20 latchup cause, effect and prevention standard. Laserinduced latchup screening and mitigation in cmos devices. Big names in eda software are synopsys, cadence, mentor, and magma here is some of the software typically involved in a standardcell asic flow. Design automation for reliable cmos chip io circuits. Msan107 understanding and eliminating latchup in cmos. An application of hardeningbydesign principles in which a spacequalified cmos product is modified, based on the pulsed laser results, to be latchup immune, is presented in detail. The problem and its cure the springer international series in engineering and computer science troutman, r. Many elementary discussions start with the basic condition for regeneration in the two transistors. Vlsi design sequential mos logic circuits logic circuits are divided into two categories.
When your power management system reapplies power, boom, the part is in latchup. The problem and its cure the springer international series in engineering and computer science. To avoid cmos latchup, numerous well and substrate contacts are placed close to the source connections of the nmospmos devices. Jan 19, 2015 keith sabine, product manager at eda firm pulsic, discusses circuit latchup and its prevention. His experience covers the effects of the natural space single event upset, latchup, gate rupture and burnout due to cosmic rays and electrostatic discharge, and nuclear radiation upset, latchup, and burnout due to system generated electromagnetic pulse sgemp, and neutron and gamma rays on devices and systems ranging from analytical.
Soc manufacturers have always endeavored to reduce the feature size through technology and topology. Speaking about cmos transistors, latch up is the phenomenon of low impedance path between power rail and ground rail due to interaction between parasitic pnp and npn transistors. Jun 18, 2012 the cmos structure is analyzed and the pnp and npn latching transistors are identified. Cmos circuitry dissipates less power than logic families with resistive loads. Aug 01, 2017 this lecture discusses latchup phenomenon in smos circuits. Methodology on extracting compact layout rules for latchup. What is latchup, what are typical methods to mitigate latchup and layout changes for conventional bulk silicon technology. Click download or read online button to get cmos latch up modeling and prevention book now. Latchup refers to short circuit formed between power and ground rails in an ic leading to high current and damage to the ic. It does not matter if the cmos ic is a microcontroller, an operational amplifier, an analogtodigital converter adc, logic, or analog multiplexor. Latchup failure is one of these problems, when triggered, causing systemwide or destructive malfunction, threatening the reliability of a cmos design.
Cmos technology and logic gates mit opencourseware. The book all semiconductor device engineers must read to gain a practical feel for latchup induced failure to produce lowercost and higherdensity chips. More than ten testchips with different latchup test struc. Q1 and q2 are parasitic transistor elements residing inside it. Another solution is to put schottky diode clamps in the wires to prevent them from going more than 0. Latch up is a state where a semiconductor undergoes a highcurrent state or low impedance path as a result of interaction of pnp and npn bipolar transistors. A problem which is inherent in the pwell and nwell processes is due to relatively large number of junctions which are formed in these structures, the consequent presence of parasitic diodes and transistors. The book provides engineers involved in the design of cmos technologies with a good understanding of the device physics of latchup and the techniques available to avoid it.
Ece 4420 latchup page 1 latchup in cmos technology latchup mechanisms. It resulted in circuits either malfunctioning or consuming excessive power, and could be either inherent in the design or triggered by voltage spikes on io pads that could forward bias pn. Power management can cause latchup in cmos chips edn. So with this definition in my head, i am trying to figure out factors that will help me prevent latchup in cmos devices. Utilization of an electronic circuit simulator in cmos latchup studies. Cmos refers to both a particular style of digital circuitry design and the family of processes used to implement that circuitry on integrated circuits chips. Electrical overstress, and transient latchup pulse generator system, circuit, and.
Mythic takes analog fastspice and symphony from mentor for ai design, siemens. Formation of parasitic bjt in cmos process has been explained first then latchup triggering mechanism has been explained with the help of. Transientinduced latchup in cmos integrated circuits. If you turn off vcc, a volt applied to the output will cause current to flow, perhaps as it drags the vcc voltage up, but current flows nevertheless. Single event upset and latchup consider for cmos devices. Latchup is the creation of a low impedance path between the power supply rails. To prevent latchup in cmos chips you can put highvalue resistors between the inputs and outputs a. Under normal bias, the parasitic scr is in its blocking state but, if subjected to a large voltage spike or if exposed to an ionizing environment, triggering may occur. Additionally, the thyristor might be triggered by a high supply voltage far higher than the value given in.
Transientinduced latchup in cmos integrated circuits the book all semiconductor device engineers must read to gain a practical feel for latchup induced failure to produce lowercost and higherdensity chips. All cmos ics have latchup paths, but there are several design techniques that reduce susceptibility to latchup. When you turn off the circuit block, with zero volts across the logic gates there can be no leakage. Currently do not have any solid way how verify by simulation, what margin of safety i have in regard to latchup. In cmos processes, these transistors can create problems when the combination of nwellpwell and substrate results in the formation of parasitic npnp struct.
Additionally, the thyristor might be triggered by a high supply voltage far higher than the value given in data sheets. This concern is becoming more widespread with the ascendency of cmos as the dominant vlsi technology, particularly as parasitic bipolar characteristics continue to improve at ever smaller dimensions on silicon wafers with ever lower defect densities. There are multiple reasons for its emergence to its current status, continuous reduction in feature size being one of them. The potential for latchup, a pnpn selfsustaining low impedance state, is inherent in standard bulk cmosintegrated circuit structures. This is one reason switching a chunk of cmos circuitry on and off to save power can cause latchup. This is what was unsatisfactory in the first diagram, it showed theparasitic transistors you end up with, but not how they get formed outof a cmos circuit made from mosfets. In some cases latchup can be a temporary condition that can be resolved by power cycle, but unfortunate. Transientinduced latchup in cmos integrated circuits equips the practicing engineer with all the tools needed to address this regularly occurring problem while becoming more proficient at ic layout. A latchup is a type of short circuit which can occur in an integrated circuit ic. Singleevent latchup protection of integrated circuits tech. Modeling latchup in cmos integrated circuits ieee xplore. Latchup test considerations for analogtodigital converters a. Similarly, if you drag the outputs of a cmos chip above or below the power supply rails you can latchup the part. Q1 is double emitter pnp transistor whose base is formed by n well substrate of pmos, two emitters are formed by source and drain terminal of pmos and collector is formed by substratep type of nmos.
Simple circuit techniques and attention to system design details will ensure that the cmos full potential can be realized in all operating environments. He has also participated as a member of technical program committee. In cmos, these transistors acts as parasitic elements. Speaking about cmos transistors, latch up is the phenomenon of low impedance path between power rail and ground rail. Latchup cause, effect and prevention allthingsvlsi. Todays computer memories, cpus and cell phones make use of this technology due to several key advantages. Cmos latch up modeling and prevention download ebook pdf. A costeffective hv power ic design requires an advanced approach based on iterative blocklevel verification, with hv latchup rules involving new principles that combine both topological and electrical. Early cmos processes suffered a reliability concern that became known as latchup. If you see examples here that are not in your installation you should consider updating to a later version of the software. This will be helpful in developing an understanding of the relationships between external circuit and system conditions and the resultant triggerng of latchup in cmos devices.
Shown alongside is a cmos transistor consisting of an nmos and a pmos device. Latchup test considerations for analogtodigital converters. Nowthat you understand the physics of latchup, you can see how it starts. In modern cmos processes there are various protection mechanisms against latchup sti, guard rings, keeping track of the resistance of the well contacts etc, but i am not certain to what degree these protect in this use case. If the s is equal to v oh and the r is equal to v ol, both of the parallelconnected transistors m1 and m2 will be on. By having a high conductivity path from vdd to gnd in the cmos structure, you could potentially damage the device and it would never recover.
Tong li, chinghan tsai, elyse rosenbaum, sungmo kang, substrate modeling and lumped substrate resistance extraction for cmos esd latchup circuit simulation, proceedings of the 36th annual acmieee design automation conference, p. Slya014a latchup, esd, and other phenomena 5 the parasitic thyristor can be triggered by a rapid rise of the supply voltage. He pointed out that the part was welldesigned and recovered gracefully from the latchup, but the fact that the esd diode was forward biased for a few nanoseconds still would. In some cases latchup can be a temporary condition that can be resolved by power cycle, but unfortunately it can also cause a fatal chip failure. When this chapter is completed, the following chapters will spiral backward into more depth, on each individual area from models, testing and tools. Cmos sr latch based on nor gate is shown in the figure given below.
Finally, the author offers device and design techniques to avoid latchup in cmos integrated circuits. Sometimes the part heats up, but when you remove all power and signals, the chip has survived the latchup condition. Jan 19, 2015 early cmos processes suffered a reliability concern that became known as latchup. Damage in metal layer of an integrated circuit after a single event latchup of. In cmos technology, there are a number of intrinsic bipolar junction transistors.
Junctions between the doped regions and the substrate that dont contribute to the cmos architecture are considered parasitic and can lead to a number of problems. Simply defined, latchup is a functional chip failure associated with excessive current going through the chip, caused by weak circuit design. Latchup is a state where a semiconductor device undergoes a highcurrent state as a result of interaction between a pnp and an npn bipolar transistor. Cmos latchup guard rings latchup latchup causes latchup effects latchup prevention. Hdl simulators read an rtl description of the design typically written in verilog or vhdl and mimic the behavior of the hardware described by the rtl. Assuming you have a picture of the parasitic bjts as a reference which can be found in most cmos text book explaning latchup. In this chapter, electronic design automation eda techniques and methods for electrostatic discharge, electrical overstress eos, and latchup are discussed. Figure 1 to prevent latchup in cmos chips you can put highvalue resistors between the inputs and outputs a. In cmos fabrication, latchup is a malfunction which can occur as a result of improper design.
The term cmos stands for complementary metal oxide semiconductor. What is latch up and how to test it october 01, 20, anysilicon simply defined, latchup is a functional chip failure associated with excessive current going through the chip, caused by weak circuit design. Cmos technology is one of the most popular technology in the computer chip design industry and broadly used today to form integrated circuits in numerous and varied applications. What is latch up in cmos design and ways to prevent it. Latchup in integrated circuits from energetic protons. More specifically it is the inadvertent creation of a lowimpedance path between. Cmos technology working principle and its applications. Basic considerations many cmos circuits are sensitive to latchup from heavy ions, and latchup is one of the major.
Edn power management can cause latchup in cmos chips. Cmos circuit design, layout, and simulation and cmos mixedsignal circuit design quick links. The invention of the now industrystandard technique to prevent cmos latchup was made by hughes aircraft company in 1977. Such an understanding often helps to organize the practical experience to be effective.
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