EEPROMs: An Upgrade from EPROMs

The ongoing progress in technology constantly pushes the need for better memory storage options, leading to the development from EPROM to EEPROM. This article explores the basic principles and how EPROM and EEPROM work, comparing their structures, how they erase data, and how they are used in different technologies. It also looks at the move from EPROM that uses ultraviolet light to erase data, to EEPROM that makes it easier for users by allowing data to be erased electrically. This change not only shows technological growth but also solves the practical problems of EPROM, helping to create more durable and flexible electronic devices.

Catalog

Figure 1: EPROM Memory

What Is the EPROM and EEPROM Technologies?

Erasable Programmable Read-Only Memory (EPROM) and Electrically Erasable Programmable Read-Only Memory (EEPROM) are important types of memory that don’t lose their data when the power is turned off. They have played a big role in the growth of electronic devices.

EPROM, created in the mid-1970s, was a major step forward because it allowed memory to be reused. Before EPROM, a memory chip could only be programmed once. With EPROM, you could erase the data and program it again by exposing the chip to strong ultraviolet (UV) light. This made it possible to update or fix devices without needing to replace the memory chip.

EEPROM came out in the late 1970s and improved things even more by letting you erase and rewrite data using an electrical charge instead of UV light. This made it easier to update memory because you could change specific parts of the data without affecting the rest. EEPROM is more flexible and useful for many different purposes because you can update the data directly within the device.

Figure 2: EEPROM Memory

Importance of Non-Volatile Memory in Modern Electronics

In everyday electronics like smartphones and computers, Non-volatile memory (NVM) stores important information like settings and software that need to stay intact even when the device is turned off. This ensures that users don’t lose their data and can pick up right where they left off after a power outage.

In industrial and automotive settings, NVM is good for storing data that ensures machines and vehicles run safely and continuously. This memory protects any information during power outages or system resets, ensuring smooth operations.

As more devices connect through the Internet of Things (IoT), the demand for reliable memory that keeps data even when powered off has increased. These devices depend on stored data to operate independently.

Moreover, this type of memory can be reprogrammed, allowing devices to be easily updated with new features without changing the hardware. This makes electronics more sustainable and adaptable, allowing them to evolve to meet users' needs.

Figure 3: Volatile and Non-Volatile Memory

How EPROM Stores Data Without Power?

EPROM (Erasable Programmable Read-Only Memory) is a type of non-volatile memory used in computers and electronic devices to store data that must be preserved even when the device is turned off. Being non-volatile means that EPROM retains its data without needing a constant power supply. Unlike PROM (Programmable Read-Only Memory), which can only be written to once, EPROM can be erased and reprogrammed multiple times.

The technology behind EPROM is based on an array of transistors, each representing a bit of data. An element in each transistor is the floating gate, an electrically isolated component that plays an important role in data storage. The presence or absence of charge on the floating gate alters the transistor’s threshold voltage. If the threshold voltage is sufficiently high, the transistor switches on, indicating a binary "1". If not, it remains off, indicating a binary "0".

EPROM's ability to retain data without power relies on the floating gate's design. The charge on the floating gate is trapped and remains stable for years due to an oxide layer that electrically isolates it, preventing any leakage. This isolation ensures that the stored data is preserved without a power source until the memory is deliberately erased.

Figure 4: EPROM Programmer Circuit Diagram

How EPROM is Programmed Using Hot Electron Injection?

Programming an EPROM involves changing the state of the floating gates within its transistor array. This is achieved through a technique called hot electron injection, requires applying a higher-than-normal voltage to the transistors' drains. This elevated voltage accelerates electrons within the channel between the source and drain, giving them high kinetic energy.

Some of these energized electrons, referred to as "hot electrons", gain enough momentum to penetrate the thin oxide layer separating the channel from the floating gate. Once they pass through this barrier, they become trapped in the floating gate, thereby raising its threshold voltage. This increase in voltage effectively changes the transistor’s state to represent a binary "1".

This method allows for precise control over which bits are set to "1" during EPROM programming. The data, once written, remains stored as charge on the floating gates, unaffected by the power supply until the memory is intentionally erased. Erasure involves exposing the EPROM to ultraviolet (UV) light, provides enough energy to free the trapped electrons and resetting the transistor states back to "0".

Figure 5: : EPROM Internal Structure

Data Erasing Process of EPROM

Erasing an EPROM is not as simple as overwriting data on a flash drive. Instead, it involves using ultraviolet (UV) light, relies on the photoelectric effect to restore the chip to its original, unprogrammed state.

Each EPROM chip is equipped with a small quartz window that allows UV light to reach the silicon layer where the data is stored. Data in an EPROM is stored in floating-gate transistors. When the chip is exposed to UV light, photons from the light have enough energy to excite electrons in the floating gate, causing them to escape. This process resets the transistor to its initial state, effectively erasing the stored data and leaving the chip ready to be reprogrammed. The transistor can then be recharged or left uncharged, representing binary values of 0 and 1.

The UV light used to erase EPROMs typically has a wavelength of about 253.7 nanometers, falls within the UVC range. This specific wavelength is effective in providing the energy required to clear the stored charges in the transistors. The erasure process takes 10 to 30 minutes, depending on the intensity of the UV light and the specific EPROM model. During this period, the entire chip must be evenly exposed to the UV light to ensure that all the data is fully erased, leaving the chip ready for fresh programming.

Figure 6: UV EPROM Eraser

Limitations of EPROM and the Shift to Modern Memory Technologies

Even though EPROMs can be reused they have some drawbacks because of how they need to be erased and reprogrammed. A big problem is that you have to physically take the EPROM out of its device to erase it. This is because UV light has to shine directly on the silicon through a quartz window, usually hard to reach when the chip is on a circuit board. Taking out the EPROM causes issues like downtime, as the device needs to be turned off and partially taken apart to reach the chip, which can be a problem in some situations. There's also a risk of damaging the chip or its pins during removal, and electrostatic discharge (ESD) could harm the electronic parts. The process also requires skilled workers to handle the UV erasing equipment correctly and to put the chip back in without causing damage. Moreover, in large systems or devices with many EPROMs, erasing and reprogramming each chip one by one can take a lot of time and might not be practical. These challenges led to the creation of other memory types like EEPROM and flash memory that can be erased and reprogrammed without needing to remove them from the circuit. These alternatives are easier to use and more flexible, but they might not be as durable or could be more expensive.

Applications of EPROMs in Technology

Storing BIOS in Computers

The BIOS (Basic Input/Output System) is important software that helps a computer's operating system communicate with its hardware. EPROMs are used to store the BIOS because they keep data even when the computer is turned off. When you start a computer, the BIOS in the EPROM turns on the hardware and handles basic tasks until the operating system takes over. It makes sure the computer can start up and work properly.

EPROMs also let the BIOS be updated through a process called "flashing." This means the BIOS can be changed if there are problems or new features are required, without having to change the hardware. This ability makes computers more long-lasting and adaptable.

Firmware Storage for Modems and Video Cards

EPROMs are also used in modems and video cards to store firmware, a specialized software that directly controls the hardware. In modems, the software stored on an EPROM controls how digital signals are converted to and from analog signals, making it possible to communicate over phone lines. This software is important because it lets the modem work with different data protocols and speeds, ensuring it works correctly with various communication standards.

Similarly, in video cards, EPROMs store firmware that governs the operations of the graphics processing unit (GPU). This firmware is responsible for managing basic display functions and handling graphic processing tasks. By storing this firmware on an EPROM, manufacturers ensure that the video card can be updated to support new software and operating systems, which helps the device last longer.

Early Use in CPUs

During the early days of computer development, EPROMs were used to store the microcode for central processing units (CPUs). Microcode is a set of low-level instructions that dictate how the CPU executes higher-level machine code instructions. These instructions are required to the CPU’s ability to perform tasks, as they define the core logic and operational protocols.

By using EPROMs to store microcode, manufacturers could improve and update the CPU’s functions without having to change the actual hardware. This was useful in the early days of computer technology when things were advancing quickly and processors need to be adjusted often.

EEPROM Characteristics

EEPROM differs from other types of non-volatile memory, such as ROM (Read-Only Memory) and flash memory, primarily in how it can be modified. ROM is programmed during manufacturing and cannot be altered afterward. On the other hand, EEPROM can be rewritten and erased electrically, offering greater flexibility. Unlike EPROM that requires exposure to strong ultraviolet light for erasure, EEPROM allows these modifications without the need for physical intervention and making it more convenient for updating device configurations or applying software patches.

Figure 7: EEPROM Memory Circuit Diagram

EEPROM Memory Capacity and Structure

Data in EEPROM is stored in small units, like bytes or word level, so you can erase and rewrite specific parts without affecting the rest. This is a big improvement over older memory types like EPROM, where you had to erase large sections or the entire memory all at once.

Inside EEPROM, there's a grid of memory cells, each holding a bit of data. These cells use a special type of transistor called a floating gate transistor to store the information. Data is saved by adding or removing electrons from the floating gate. The number of electrons changes the transistor's threshold voltage, which is the voltage need to turn it on, allowing it to store a binary value (either 0 or 1).

Figure 8: EEPROM Memory Cell

To write data to EEPROM, a higher voltage than usual is applied, causing electrons to move through a thin layer of material into the floating gate, a process called Fowler-Nordheim tunneling. Once the electrons are trapped in the floating gate they stay there because the surrounding material insulates them, keeping the data safe.

To erase data, the process is reversed. A negative voltage is applied that pulls the electrons out of the floating gate, erasing the stored data and resetting the transistor's threshold voltage back to its original state.

EEPROM memory cells work mainly because of two parts: the floating gate and the control gate.

Floating Gate: The floating gate is a tiny, electrically isolated part of the transistor that sits between the control gate and the transistor's channel. Its main function is to hold a charge by trapping electrons within its structure. This gate is surrounded by an insulating oxide layer, prevents the electrons from escaping. The presence or absence of electrons on the floating gate changes the threshold voltage of the transistor, thereby encoding data as a binary '1' or '0'. The floating gate is part of the memory cell that actually stores the data.

Figure 9: Floating Gate and Control Gate in EEPROM

Control Gate: The control gate is the external gate electrode that controls the writing and erasing of data. During the writing process, the control gate is used to apply a voltage that forces electrons to tunnel through the oxide layer and onto the floating gate. During the erasing process, a voltage of the opposite polarity is applied, and removes electrons from the floating gate. The control gate, therefore, serves as the interface that allows external circuits to interact with the floating gate, making it possible to read, write and erase data.

The data storage capabilities of EEPROMs are heavily dependent on the interaction between the floating gate and the control gate. The floating gate securely stores the data by trapping electrons, while the control gate allows for precise control over the reading, writing, and erasing processes. This interaction ensures that EEPROMs are a reliable and flexible option for non-volatile data storage.

EEPROM Programming and Erasing Process

Erasing data from an EEPROM involves removing electrons from the memory cells without taking the chip out of the device. This is done by applying an erase voltage that is the opposite of the voltage used to write data.

During erasing, a strong negative voltage is applied to one part of the chip, while another part is kept at a higher voltage. This creates a powerful electric field that makes the electrons leave the memory cells and go back into the chip’s material. This action resets the memory, bringing it back to its original state, represents a "1" or an erased state.

The advantage of being able to erase data without removing the EEPROM chip is that it allows for easy and efficient updates. Data can be erased and rewritten while the device is still running, that is important for tasks that need regular updates like adjusting settings or storing calibration data without stopping the device.

In short, EEPROM uses a process that moves electrons in a controlled way to erase and write data. This, along with the ability to erase data without removing the chip, makes EEPROM very useful in many electronic devices.

Applications of EEPROM

• Firmware Updates: Stores the software controlling hardware, allowing updates without replacing hardware, good for long-lasting devices.

• Device Configuration: Retains device settings after power loss, ensuring consistent operation, as seen in routers storing network settings.

• Calibration Data Storage: Maintains important calibration data in precision instruments, ensuring accuracy over time despite environmental changes.

• Consumer Electronics: Remembers user settings in everyday devices like microwaves, enhancing convenience and user experience.

• Automobiles: Stores data such as odometer readings and radio presets, ensuring these settings persist after the car is turned off.

• Personal Computing Devices: Found in BIOS to store any settings need for computers to boot up and operate correctly.

• Smart Cards and Identification: Securely stores information like PINs and access keys, providing both safety and quick accessibility in smart cards.

Comparison of EPROM and EEPROM Memory Technologies

Figure 10: EPROM and EEPROM Memory

Aspect	EPROM	EEPROM
Type of Memory	Non-volatile	Non-volatile
Programming Method	Requires higher voltages	Standard electrical charges
Erasing Method	UV light exposure through a quartz window	Electrical erasing, no need for UV light
Data Erasure	Entire chip is erased at once	Byte-level erasure
Chip Removal	Requires removal from the circuit for erasing	Can be updated directly in-circuit
Rewriting Capability	Requires UV light exposure and reprogramming	Rewrites electrically, allowing for easy updates
Durability	Less durable due to UV light exposure degrading the chip	More durable with longer lifespan due to electrical erasing
Practicality for Frequent Updates	Less practical, as it requires full chip erasure and reprogramming	More practical, allows frequent updates and selective modifications
Applications	Older or specialized devices requiring infrequent updates	Modern devices, household appliances, firmware in networking equipment

Conclusion

The shift from EPROM to EEPROM is an important step forward in memory technology, solving many problems of older memory types. EEPROM is more flexible, durable, and easier to use, best for the needs of today's electronic devices. It allows changes to be made quickly and efficiently without having to remove the chip or use UV light. This makes it easier for devices to keep up with fast-changing technology and get ready for the future. The development of EEPROM shows a move towards creating more efficient, user-friendly electronics, helping to drive ongoing innovation in memory technology.

Frequently Asked Questions [FAQ]

1. Can EPROM be changed?

EPROM can be altered but not with the same ease as other types of programmable memory. To change the data stored in an EPROM, you need to expose it to strong ultraviolet light through a window designed for this purpose, found on the top of the chip. This process erases the existing data, allowing new data to be programmed. However, this is not a trivial task and requires specific equipment and conditions, unlike more modern EEPROMs or flash memory.

2. Is EEPROM faster than flash?

EEPROM and flash memory have comparable speed characteristics, but EEPROM can be slower for write operations. This is because EEPROM allows data to be written and erased at the level of individual bytes, which provides flexibility but can be slower. Flash memory, on the other hand, erases and writes data in blocks, making these operations generally faster but less precise in terms of the data volume managed per operation.

3. How long will EEPROM last?

The longevity of EEPROM is high. It can retain data for about 20 to 25 years under normal conditions. However, this can vary based on factors such as the quality of the EEPROM, the environmental conditions it is exposed to, and how frequently it is accessed for writing or erasing operations. Data retention is one of EEPROM's strong suits, making it suitable for applications where long-term data storage is required without frequent changes.

4. How many times can an EEPROM be erased?

The endurance of an EEPROM, or how many times it can be erased and rewritten, varies by specific chip design but ranges from about 100,000 to 1,000,000 erase/write cycles. This makes EEPROM good for applications that require data to be frequently updated, though not as high-frequency as some newer types of memory like certain flash memories that can sustain even more cycles.

5. Is SSD an EEPROM?

No, an SSD (Solid State Drive) is not categorized as an EEPROM. SSDs generally use NAND-type flash memory, allows for faster data access, higher capacity, and more efficient write and erase operations compared to EEPROM. While both SSDs and EEPROMs are types of non-volatile memory (meaning they retain data when power is off), their technologies and applications are different, with SSDs being the preferred choice for mass storage solutions in modern computers and devices.