How the PDK Influences Placement and Metal Usage

Welcome Joren Vaes, design engineer at SOFICS

• Simulation is critical when designing analog devices based on a PDK from the fab
• Parasitics are significant, especially with new nodes having upwards of 16 metal layers
• Chris complained about a class where the professor made them draw planar structures with graph paper with colored pencils
• Large fabs on leading edge nodes have 1800 page textbook of rules
• Because the constraints get tighter, that book gets longer for each node
• 2 nm mass production on finfet currently with TSMC
• 22 was the last classic cmos
• Finfet, looks like a devil
• ‘gate all around’ / nanosheet
• CFET (complementary field effect transistor) is next
• Joren really gets Maxwells Equations…as you have to at super high speeds
• SOFICS are making phy’s / IP blocks
• Amplifiers that are DC to 50 GHz
• Making a datasheet for the resulting IP block
• Joren got his PhD working on millimeter wave applications
• It’s all just physics
• Using coils to impedance match between layers
• Reflecting off of different materials at angles is Snells law (not lorentz equation) and that extends to different materials at different wavelengths
• Cables are very lossy at 100 GHz…dBs per cm
• Parasitics impact every part of the design process
• Wireline community – name for the high speed interfaces, including research in the space
• Most transistor threshhold voltages that Joren works with are … 750 mV!
• Voltage dependent drc rules
• Electromigration – holes in wires from electrons
• ESD is a big part of the business, and a large source of parasitics
• New product development for IP blocks
• Working with customers and Foundry at the 2 nm node
• Design companies need to be paying 100s of thousands to software providers
• After, it goes to spice and schedmatic
• Joren decides whether to jump in on layout
• LVS – layout vs schematic
• Parasitic extraction (spice netlist)
• PDKs define how you can do the layout stage
• Lower cost tools exist but more expensive tools have tooling that tells you when you’re violating DRC
• 3 main vendors
  • Cadence
  • Synopsis
  • Siemens (Calibre)
• Foundries soemtimes only support one tool
• Doing test wafers  allows testing of structures. They often get MPW at a discount from the fab (since they’re often testing new processes as well)
• How do they test with packaging options?
  • ‘low speed’ can be die bonded or pcb mounted
  • high speed does on wafer probing (with veeeery expensive probes)
• Check out Sofics.com for more info on the company. They also have a blog with a great name.
• Follow or connect with Joren on LinkedIn