MTr/mm² (mega-transistor per squared millimeter) is a transistor density unit that attempts to quantify a process node. The metric makes use of a weighted system consisting of two typical standard cells found in most libraries - a very small NAND2 cell and a very large SFF cell.

Overview

The metric was proposed by Mark Bohr, Intel's director of process architecture and integration, in 2017. The metric attempts to take into account second order design rules that the simpler density metrics such as CPPxMMP and CPPxMMPxH cannot capture because they do not represent a typical standard cell. It should be noted that the metric explicitly SRAM cell sizes because of the large variance in SRAM-to-logic ratio between popular chips. Therefore, SRAM cell sizes should be reported separately alongside the MTr/mm² unit.

Two cells that are found in every standard library are used: a very small 2-input NAND cell consisting of just four transistors and a very large scan flip-flop cell. The NAND2 is weighted as 0.6 while the SFF is weighted as 0.4.