The book all semiconductor device engineers must read to gain a practical feel for latchup induced failure to produce lowercost and higherdensity chips. 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. Additionally, the thyristor might be triggered by a high supply voltage far higher than the value given in. Parasitic lateral pnp and vertical npn bjts in a pwell cmos technology.
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. By matthew hogan, mentor graphics latchup detection is challenging. Latchup refers to short circuit formed between power and ground rails in an ic leading to high current and damage to the ic. Latchup test considerations for analogtodigital converters a. Further, if a few simple precautions are taken at the design stage, then latchup can be completely avoided. Latchup becomes a real problem when you try to power up and down different sections of your design to save power. 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. Soc manufacturers have always endeavored to reduce the feature size through technology and topology. 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. Jun 18, 2012 the cmos structure is analyzed and the pnp and npn latching transistors are identified. Latchup failure is one of these problems, when triggered, causing systemwide or destructive malfunction, threatening the reliability of a cmos design.
Insection iii, a new methodology to extract compact layout rules for latchup prevention is therefore proposed to save chip size 10, 11. Request pdf latchup complementary metaloxide semiconductor cmos. The problem and its cure the springer international series in engineering and computer science troutman, r. 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. Every software package contains a full set of examples suitable for that version and are installed with the software. The general features of a lumped element latchup model are discussed. The book all semiconductor device engineers must read to gain a practical feel for latchupinduced failure to produce lowercost and higherdensity chips. Cmos technology and logic gates mit opencourseware. Todays computer memories, cpus and cell phones make use of this technology due to several key advantages. More than ten testchips with different latchup test struc. Early cmos processes suffered a reliability concern that became known as latchup. Aug 01, 2017 this lecture discusses latchup phenomenon in smos circuits. Modeling latchup in cmos integrated circuits ieee xplore. Jan 19, 2015 early cmos processes suffered a reliability concern that became known as latchup.
Formation of parasitic bjt in cmos process has been explained first then latchup triggering mechanism has been explained with the help of. Throughsoftware sel detection delay measurements of the seltc. A latchup is a type of short circuit which can occur in an integrated circuit ic. Lambdabased designs are scaled to the appropriate absolute units depending on the manufacturing process finally used. Latchup is caused by the triggering of parasitic bipolar structures within an integrated circuit when applying a current or voltage stimulus on. Latchup is a condition where a low impedance path is created between a supply pin and ground.
Vlsi design sequential mos logic circuits logic circuits are divided into two categories. 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. 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. April 1995 single event upset and latchup considerations for cmos devices operated at 3. Design automation for reliable cmos chip io circuits. Latchup, esd, and other phenomena 5 the parasitic thyristor can be triggered by a rapid rise of the supply voltage. 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.
All cmos ics have latchup paths, but there are several design techniques that reduce susceptibility to latchup. 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. This effect often was observed in earlier generations of cmos circuits. 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. When your power management system reapplies power, boom, the part is in latchup. 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. To understand latch up we need to understand the various parasitic components in a cmos. 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. Mythic takes analog fastspice and symphony from mentor for ai design, siemens. Typical criterion is less than 10% change of all powersupply currents and passing of a full functional test program. Cmos latchup guard rings latchup latchup causes latchup effects latchup prevention. 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. Such an understanding often helps to organize the practical experience to be effective.
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. Ece 4420 latchup page 1 latchup in cmos technology latchup mechanisms. Latchup has been, and continues to be, a potentially serious cmos reliability concern. Click download or read online button to get cmos latch up modeling and prevention book now.
He has also participated as a member of technical program committee. 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. 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. 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. 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. Laserinduced latchup screening and mitigation in cmos devices. Another solution is to put schottky diode clamps in the wires to prevent them from going more than 0. Many elementary discussions start with the basic condition for regeneration in the two transistors. 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. The cmos latch schematic is drawn and the triggering methods are discussed. In this chapter, electronic design automation eda techniques and methods for electrostatic discharge, electrical overstress eos, and latchup are discussed.
Latchup test considerations for analogtodigital converters. Simple circuit techniques and attention to system design details will ensure that the cmos full potential can be realized in all operating environments. 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. 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. Ker and hsu introduce the phenomenon and basic physical mechanism of latchup, explaining the critical issues that have resurfaced for cmos. Jan 19, 2015 keith sabine, product manager at eda firm pulsic, discusses circuit latchup and its prevention. So with this definition in my head, i am trying to figure out factors that will help me prevent latchup in cmos devices. Slya014a latchup, esd, and other phenomena 5 the parasitic thyristor can be triggered by a rapid rise of the supply voltage. Latch up is basically a positive feedback circuit made up of the paracitic npn and pnp inside your cmos. May 04, 20 latchup cause, effect and prevention standard. 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.
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. 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. Damage in metal layer of an integrated circuit after a single event latchup of. Cmos technology working principle and its applications. Shown alongside is a cmos transistor consisting of an nmos and a pmos device. Q1 and q2 are parasitic transistor elements residing inside it. Single event upset and latchup consider for cmos devices. Singleevent latchup protection of integrated circuits tech. A new cad software package for fullchip esd protection circuit verification.
What is latch up in cmos design and ways to prevent it. It does not matter if the cmos ic is a microcontroller, an operational amplifier, an analogtodigital converter adc, logic, or analog multiplexor. Vlsi design sequential mos logic circuits tutorialspoint. In some cases latchup can be a temporary condition that can be resolved by power cycle, but unfortunate. Edn power management can cause latchup in cmos chips. Cmos circuitry dissipates less power than logic families with resistive loads. Currently do not have any solid way how verify by simulation, what margin of safety i have in regard to latchup. Simply defined, latchup is a functional chip failure associated with excessive current going through the chip, caused by weak circuit design. Methodology on extracting compact layout rules for latchup. More specifically it is the inadvertent creation of a lowimpedance path between.
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. Sometimes the part heats up, but when you remove all power and signals, the chip has survived the latchup condition. Transientinduced latchup in cmos integrated circuits wiley. 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. If you see examples here that are not in your installation you should consider updating to a later version of the software. Utilization of an electronic circuit simulator in cmos latchup studies. Speaking about cmos transistors, latch up is the phenomenon of low impedance path between power rail and ground rail.
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. The invention of the now industrystandard technique to prevent cmos latchup was made by hughes aircraft company in 1977. The properties of the parasitic bipolar transistors determine the conditions for latchup, and depend on layout and design rules for specific processes. To prevent latchup in cmos chips you can put highvalue resistors between the inputs and outputs a. Cmos sr latch based on nor gate is shown in the figure given below. Big names in eda software are synopsys, cadence, mentor, and magma here is some of the software typically involved in a standardcell asic flow. Latchup cause, effect and prevention allthingsvlsi. Cmos circuit design, layout, and simulation and cmos mixedsignal circuit design quick links. 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.
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. 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. Overall, latchup design rules, standards, and checker descriptions infrequently explain the reasoning behind their methodological steps in conjunction with real design. Electrical overstress, and transient latchup pulse generator system, circuit, and. When this chapter is completed, the following chapters will spiral backward into more depth, on each individual area from models, testing and tools. The potential for latchup, a pnpn selfsustaining low impedance state, is inherent in standard bulk cmosintegrated circuit structures. 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. 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. 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. Cmos latch up modeling and prevention download ebook pdf. Latchup refers to short circuit formed between power rails in an ic leading to high current and damage to the ic. To avoid cmos latchup, numerous well and substrate contacts are placed close to the source connections of the nmospmos devices. Analog esd and latchup design rule checking and verification. 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. Nowthat you understand the physics of latchup, you can see how it starts. It resulted in circuits either malfunctioning or consuming excessive power, and could be either inherent in the. However, when properly applied, cmos devices are quite insensitive to actual conditions that exist in most systems. Basic considerations many cmos circuits are sensitive to latchup from heavy ions, and latchup is one of the major. 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.
In cmos technology, there are a number of intrinsic bipolar junction transistors. Prior to discussing latchup in cmos devices, it is advantageous to brie. Finally, the author offers device and design techniques to avoid latchup in cmos integrated circuits. Latchup in integrated circuits from energetic protons. 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. 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. Remember that to turn on a npn or a pnp, you just need to have that vbe voltage. There are multiple reasons for its emergence to its current status, continuous reduction in feature size being one of them. Additionally, the thyristor might be triggered by a high supply voltage far higher than the value given in data sheets. 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.
In cmos, these transistors acts as parasitic elements. 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 term cmos stands for complementary metal oxide semiconductor. In cmos processes, these transistors can create problems when the combination of nwellpwell and substrate results in the formation of parasitic npnp struct. Cmos technology has evolved as the top choice for chip manufacturers. Latchup control in cmos integrated circuits conference. The problem and its cure the springer international series in engineering and computer science. When you turn off the circuit block, with zero volts across the logic gates there can be no leakage. 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.
Transientinduced latchup in cmos integrated circuits. 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. In recent years, the latchup is not a problem courtesy to the. The modeling of latchup with circuit simulation programs is addressed in this paper.
Power management can cause latchup in cmos chips edn. 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. Msan107 understanding and eliminating latchup in cmos. Paul rako of atmel explains how power management can cause latchup in cmos chips. Similarly, if you drag the outputs of a cmos chip above or below the power supply rails you can latchup the part. In cmos fabrication, latchup is a malfunction which can occur as a result of improper design. Miyahira jet propulsion laboratory california institute of technology pasadena, california i. This is one reason switching a chunk of cmos circuitry on and off to save power can cause latchup. Latchup is the creation of a low impedance path between the power supply rails. Figure 1 to prevent latchup in cmos chips you can put highvalue resistors between the inputs and outputs a. I went to that selfsame ic designer that had struggled with latchup on his design. What is latchup, what are typical methods to mitigate latchup and layout changes for conventional bulk silicon technology.
1137 287 449 33 1308 1285 1280 950 790 587 672 225 989 537 358 1445 1131 637 80 704 937 1246 402 1093 1365 224 1382 387 1281 747 37 1342