Why Boundary cells are needed between memory in physical design

Here is the info about the boundary cells. 

 In physical design, boundary cells are placed between memory cells or regions of memory to address several key challenges related to chip design, signal integrity, and manufacturing. The main reasons for placing boundary cells between memory regions are:

1. Isolation and Guard Bands

Boundary cells help create isolation between memory regions and other parts of the circuit. This isolation is essential to prevent interference between different functional blocks. For example, memory cells are sensitive to noise and should be shielded from noisy digital or analog circuits. Boundary cells can serve as a buffer zone to protect memory from signals that could cause disruption.

2. Driving Large Capacitive Loads

Memory cells, especially in SRAM or DRAM arrays, have high capacitive loads. Boundary cells are often used to drive these loads more effectively. These cells can be designed to handle the large capacitances associated with the memory elements and provide strong signal driving capabilities, improving the overall performance of the memory.

3. Signal Integrity and Voltage Level Translation

Boundary cells can help improve signal integrity between different parts of the design. They may be responsible for ensuring proper voltage level translation and driving signals at the correct levels, preventing issues like signal degradation or incorrect voltage interpretation between different regions.

4. Floorplanning and Space Management

Boundary cells can also be part of the overall floorplanning strategy. They may be inserted at the edges of memory blocks to facilitate routing and manage the available space. These cells can make it easier to connect different parts of the chip by providing extra space for the metal layers and reducing congestion at the boundaries of memory areas.

5. Power Distribution and Decoupling

Memory regions are typically power-hungry and require stable power delivery. Boundary cells are sometimes used for power decoupling, ensuring that noise or fluctuations in the power supply do not affect memory performance. These cells can help to distribute power more evenly and provide a stable environment for memory cells to operate.

6. Testability

Boundary cells can serve as important elements for improving the testability of memory structures. They are often used to include extra logic that facilitates easier testing of the memory during manufacturing. This can include cells that are part of Built-In Self Test (BIST) or test access mechanisms, which are critical for validating the memory's performance and functionality before final production.

7. Redundancy

Boundary cells can be used in cases of memory redundancy to improve yield. For example, if certain memory cells are found to be defective during testing, boundary cells can help connect spare memory cells to replace the defective ones. This redundancy helps in increasing the overall yield of the chip and ensures that memory functions reliably in the final device.

8. Thermal Management

High-performance memory areas may generate heat, which needs to be managed efficiently. Boundary cells can be used to help in thermal management by dissipating heat or providing pathways for heat to flow away from memory regions, preventing overheating and ensuring stable performance.

In summary, boundary cells in physical design play a critical role in ensuring that memory operates efficiently, reliably, and with minimal interference from other parts of the chip. They help with power delivery, signal integrity, isolation, testability, and overall performance, making them an essential part of the physical design process.