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 refers to short circuit formed between power rails in an ic leading to high current and damage to the ic. Interest in latchup is being renewed with the evolution of complimentary metaloxide semiconductor cmos technology, metaloxidesemiconductor fieldeffect transistor mosfet scaling, and highlevel systemonchip soc integration. A t rac ed byh m nv g s o f cmos devices, designers using them for the. Pdf the impact of lowholdingvoltage issue in highvoltage. This requires more current before latchup can occur. With no free current carriers present, the depletion regions. Apr 18, 2018 for hv power analog ics, latchup codesign methods have significantly evolved from the traditional lv cmos io and core latchup base. Dec 18, 2007 latchup semiconductor process solutions for both cmos to bicmos, such as shallow trench, deep trench, retrograde wells, connecting implants, subcollectors, heavilydoped buried layers, and buried grids from single to triplewell cmos. An989 single event upset and latchup considerations for cmos devices operated at 3. Nanometer cmos ics download ebook pdf, epub, tuebl, mobi. Sini mukundan march 21, 2018 march 21, 2018 2 comments on cmos latchup. Edn power management can cause latchup in cmos chips. The two transistors are protected by resistors but if examined more closely, theres an scr device that could possibly be triggered.
Cmos process with the human body model machine model esd level of 7. Basic psubstrate cmos inverter cross section with latchup circuit model. The pnp and npn transistors can be natural to the technology, or parasitic devices. Dependence of device structures on latchup immunity in a high. Msan107 understanding and eliminating latchup in cmos.
Shown alongside is a cmos transistor consisting of an nmos and a pmos device. Cmos and bicmos circuits use nmos and pmos transistors to. Allen 2016 latchup triggering latchup of the scr can be triggered by two. An600 understanding latchup in advanced cmos logic. This causes excessive current flows and potential permanent damage. The proton latchup cross sections of these devices differed by more than two orders of magnitude. Latchup has long been a bane to cmos ic applications. In a bulk cmos chip, the core circuit blocks are always latchup sensitive due to a low holding voltage of the parasitic scr path. Latchup has been, and continues to be, a potentially serious cmos. The nmos and pmos circuits form parasitic pnpn structures that can be.
A latchup is a type of short circuit which can occur in an integrated circuit ic. Cmos devices as well as those considering cmos designs for the. 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. Latchup in integrated circuits from energetic protons. A modeling approach that takes differences in charge collection processes for longand shortrange particles into account was effective in. Prior to discussing latchup in cmos devices, it is. A cmos output circuit including a pmos transistor and an nmos transistor connected in series between a power supply voltage and a ground voltage, is formed with a resistive component for reducing occurrence of latchup. Latchup test considerations for analogtodigital converters.
Although latchup avoidance techniques have been previously itemized, there has been little quantitative evaluation of prior latchup fixes. Well you can think latch up as a short circuit between the supply and ground. The latchup condition typically requires a power cycle to eliminate the low impedance path. Ece 4420 latchup page 2 preventing latchup in a pwell technology 1. These bjts for a siliconcontrolled rectifier with positive feedback and virtually short circuit the power and the ground rail. Cmos device can directly cause latchup through base collector leakage or breakdown mechanisms. Lecture 08 latchup and esd 42516 page 086 cmos analog circuit design p.
However, the key factor in latchup sensitivity is the external resistance across the baseemitter junctions of the two parasitic transistors, not the transistor gain 11. The cmos latch schematic is drawn and the triggering methods are discussed. This article will briefly describe the causes, mechanism, and consequences of latchup and discuss available prevention methods. Latchup cause, effect and prevention allthingsvlsi. Additionally, the thyristor might be triggered by a high supply voltage far higher than the value given in data sheets. Latchup, esd, and other phenomena 5 the parasitic thyristor can be triggered by a rapid rise of the supply voltage. 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.
It happens because of the formation of two parasitic bjts one pnp and another npn in cmos. Pdf latch up effect under electromagnetic pulse researchgate. This site is like a library, use search box in the widget to get ebook that you want. Single event upset and latchup consider for cmos devices. Basically sp ak ing, y lo r dtv cf b one of the many cmos processes available, can be made to latchup if stressed severely enough. If the parasitic trace resistance r1 is large enough, the ground of the inverter can be at a higher potential than the input signal. Figure 4 an improved diagram shows the wafer substrate as the more typical ptype material. Clear methodologies that grant protection from latchup, with insight into the physics, technology and circuit issues involved, are in increasing demand. Q1 and q2 are parasitic transistor elements residing inside it. Ker and hsu introduce the phenomenon and basic physical mechanism of latchup, explaining the critical issues that have resurfaced for cmos. Understanding a few facts will resolve both of these situations. Prior to discussing latch up in cmos devices, it is. Us7221027b2 latchup prevention method for integrated. A diagram of a fourregion device in a typical nwell cmos circuit is shown in figure 1.
Cmos circuitry without major concern about latchup. Latchup current selfstop circuit for wholechip latchup. Simply defined, latchup is a functional chip failure associated with excessive current going through the chip, caused by weak circuit design. 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. Todays computer memories, cpus and cell phones make use of this technology due to several key advantages. Complementary metaloxidesemiconductor cmos, also known as complementarysymmetry metaloxidesemiconductor cosmos, is a type of metaloxidesemiconductor fieldeffect transistor mosfet fabrication process that uses complementary and symmetrical pairs of ptype and ntype mosfets for logic functions. Research and development into the causes led to several papers in the 1980s discussing causes and methods to lessen the influence of latchup. A first current shunting diode has an anode coupled to the pad and a cathode coupled to a first voltage source. In case of any spike in the power supply, one of the parasitic bjt gets on d.
The resistive component is arranged at least one of the sources of the pmos and nmos transistors so as to be connected in series with a parasitic bipolar transistor formed. More specifically it is the inadvertent creation of a lowimpedance path between the power supply rails of a mosfet circuit, triggering a parasitic structure which disrupts proper functioning of the part, possibly even leading to its destruction due to overcurrent. The following diagram is a drawing of a typical cmos circuit. Latchup in cmos technology the problem and its cure r. Click download or read online button to get nanometer cmos ics book now. Cmos technology working principle and its applications. Notice the two transistors, npn and pnp and their connection to vdd and gnd supply rails. Winning the battle against latchup in cmos analog switches. An600 understanding latchup in advanced cmos logic on. 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.
Here is a typical bulk cmos device a simple inverter now, here is the same figure showing the parasitic bjts that cause latchup. As a starting point, this discussion will be followed by. May 04, 20 here is a typical bulk cmos device a simple inverter now, here is the same figure showing the parasitic bjts that cause latchup. For hv power analog ics, latchup codesign methods have significantly evolved from the traditional lv cmos io and core latchup base. In cmos technology, these are typically parasitic devices. The cmos structure is analyzed and the pnp and npn latching transistors are identified. Proton latchup was investigated for several cmos integrated circuits, including a modern microprocessor. Utilization of an electronic circuit simulator in cmos latchup studies. In the integrated circuit, an internal circuit is disposed in a substrate and has a parasitic scr structure. The proposed latchup prevention methodology and circuit design can detect and stop the. The term cmos stands for complementary metal oxide semiconductor. Abnormal applications and misuse of cmos ics may still pose problems that the cmos vendor has little control over. The pchannel device has a parasitic pnp and the nchannel has a parasitic npn. The impact of lowholdingvoltage issue in highvoltage cmos technology and the design of latchupfree powerrail esd clamp circuit for lcd driver ics.
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. 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. Complementary semiconductor device having high switching speed and latchup free capability us5041894a en 19871223. Cmos latch up modeling and prevention download ebook pdf. The pwm source outputs a low signal to the inverter, which turns on the mosfet. 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. One aspect of high power supply voltages that is not often recognized. Slya014a latchup, esd, and other phenomena 5 the parasitic thyristor can be triggered by a rapid rise of the supply voltage. Keep the sourcedrain of the mos device not in the well as far away from the well as possible.
Latchup free esd protection design with complementary substratetriggered scr devices 81 fig. The structure formed by these resembles a silicon controlled transistor scr. A latchup current selfstop methodology and circuit design, which are used to prevent damage in the bulk cmos integrated circuits due to latchup, are proposed in this paper. Cmos available for download and read online in other formats. Vendors of cmos ics have always been aware of the latchup phenomenon and have considerably improved their designs and processes to reduce the danger of latchup occurring under normal usage. What is needed is a more general, more systematic treatment of the latchup problem. In this paper, latchupfree electrostatic discharge esd protection circuits. In this chapter, a brief overview of latchup is provided. We will provide a first quick look on what latchup is. Latchup has been, and continues to be, a potentially serious cmos reliability concern.
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. The free carriers in the base regions of the parasiticbipolar transistors are all you need to start the latchup, and once itbegins it just feeds on itself. Latchup free cmos using guarded schottky barrier pmos. To understand latch up we need to understand the various parasitic components in a cmos. Pdf the physics of cmos latchup latchup under high power microwave radiation is discussed.
At least one esd protection circuit and active area are disposed on the substrate and coupled to a pad. The book all semiconductor device engineers must read to gain a practical feel for latchupinduced failure to produce lowercost and higherdensity chips. Typical design of onchip esd protection circuits in cmos ics. Latchup is a condition where a low impedance path is created between a supply pin and ground. However, when properly applied, cmos devices are quite insensitive to actual conditions that exist in most systems. The impact of lowholdingvoltage issue in highvoltage cmos technology and the design of latchup free powerrail esd clamp circuit for lcd driver ics. 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 these bjts form a silicon controlled rectifier scr with positive feedback and virtually short circuit v dd to the ground, thus causing excessive current flows and even. Cmos input level shifting circuit with temperaturecompensating nchannel field effect transistor structure us4893164a en 198410. Troutman, cmos latchup, kluwer academic publishers. Latchupfree esd protection design with complementary substratetriggered scr devices 81 fig. Click download or read online button to get cmos latch up modeling and prevention book now.
Interest in latchup is being renewed with the evolution of complimentary metaloxide semiconductor cmos technology, metaloxidesemiconductor fieldeffect transistor mosfet scaling, and highlevel systemon. We also would like to thank the lbl 88inch cyclotron staff for beam delivery. Latch is the generation of a lowimpedance path in cmos chips between the power supply and the ground rails due to interaction of parasitic pnp and npn bipolar transistors. Kinetic energy reactive ion and nativeoxydefree processing. Co py 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. Latchupfree esd protection design with complementary. Latchupfree esd protection design with complementary substrate. Cmos technology is used for constructing integrated circuit ic chips. Conditions necessaires au declenchement du latchup. Dependence of device structures on latchup immunity in a. This effect often was observed in earlier generations of cmos circuits. These transistors are inherent in the cmos structure and cant be elim inated.
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