Friday 29 November 2019

Basic Synthesis Flow

Logic Synthesis means converting RTL (Register Transfer Level) into logic gates with the help of synthesis tool. Design compiler by Synopys is an example of synthesis tool and it is one of the widely used tool across the industries. Common examples of this process include synthesis of designs specified in hardware description languages, including VHDL and Verilog. Some synthesis tools generate bitstreams for programmable logic devices such as PALs or FPGAs, while others target the creation of ASICs. Logic synthesis is one aspect of electronic design automation.

Thursday 28 November 2019

Generation of Integrated Circuits

As number of transistor, which can be fabricated in a single chip increased through generation, We believe more transistor and more complex IC's are yet to come.

SSI  (Small Scale Integration) introduced in 1964, Having transistors 1 - 10 and logic gates 1 - 12

MSI (Medium Scale Integration) introduced in 1968, Having transistors 10 - 500 and logic gates  13 - 99

LSI (Large Scale Integration) introduced in 1971, having transistors 500 - 20000 and logic gates 100 - 9999

VLSI (Very Large Scale Integeration) introduced in 1980, having transistors 20000-1000000 and logic gates 10000 to 99999

ULSI (Ultra Large Scale Integration) introduced in 1984, having transistor 1000000 and more and logic gates 100000 and more

WSI (Wafer Scale Integration) is a means of building very large integrated circuits that uses an entire silicon wafer to produce a single "super-chip".

SoC or SOC (System On Chip) is an integrated circuit in which all the components needed for a computer or other system are included on a single chip.

3D-IC (3 Dimensional Integrated Circuit) has two or more layers of active electronic components that are integrated both vertically and horizontally into a single circuit.

NameSignificationYearTransistors numberLogic Gates number
SSIsmall-scale integration19641 to 101 to 12
MSImedium-scale integration196810 to 50013 to 99
LSIlarge-scale integration1971500 to 20 000100 to 9999
VLSIvery large-scale integration198020 000 to 1 000 00010 000 to 99 999
ULSIultra-large-scale integration19841 000 000 and more100 000 and more

Wednesday 27 November 2019

Metal Slotting


In very deep-submicron VLSI, certain manufacturing steps – notably optical exposure, resist development and etch, chemical vapor deposition and chemical-mechanical polishing (CMP)– have varying effects on device and interconnect features depending on local characteristics of the layout. To make these effects uniform and predictable, the layout itself must be made uniform with respect to certain density parameters. Traditionally, only foundries have performed the post-processing needed to achieve this uniformity, via insertion (“filling”) or partial deletion (“slotting”) of features in the layout. Today, however, physical design and verification tools cannot remain oblivious to such foundry post-processing. Without an accurate estimate of the filling and slotting, RC extraction, delay calculation, and timing and noise analysis flows will all suffer from wild inaccuracies. Therefore, future placeand-route tools must efficiently perform filling and slotting prior to performance analysis within the layout optimization loop.

A wider wire results in smaller current density and, hence, less likelihood of electromigration. Also, the metal grain size has influence; the smaller grains, the more grain boundaries and the higher likelihood of electromigration effects. However, if you reduce wire width to below the average grain size of the wire material, grain boundaries become "crosswise", more or less perpendicular to the length of the wire. The resulting structure resembles the joints in a stalk of bamboo. With such a structure, the resistance to electromigration increases, despite an increase in current density. This apparent contradiction is caused by the perpendicular position of the grain boundaries; the boundary diffusion factor is excluded, and material transport is correspondingly reduced.

However, the maximum wire width possible for a bamboo structure is usually too narrow for signal lines of large-magnitude currents in analog circuits or for power supply lines. In these circumstances, slotted wires are often used, whereby rectangular holes are carved in the wires. Here, the widths of the individual metal structures in between the slots lie within the area of a bamboo structure, while the resulting total width of all the metal structures meets power requirements.

What is the Need of Metal slotting

  1. To maintain the reliability during manufacturing
  2. To overcome mechanical and thermal stress during manufacturing

How Metal slotting is done

  1. Determining long and wide wires, based on foundry rules and foundry capability to manufacture
  2. Place and route tools perform metal filing and slotting with utmost optimization