• Your computer's BIOS chip
• Compact Flash (most often found in digital cameras)
• Smart Media (most often found in digital cameras)
• Memory Stick (most often found in digital cameras)
• PCMCIA Type I and Type II memory cards in laptops
• Memory cards for video game consoles

• It is noiseless
• It allows faster access
• It is smaller in size
• It is lighter

Dynamic Random-access Memory (DRAM):
The basic building block of any memory circuit is the cell in which a single bit of information is stored. The DRAM has the simplest cell structure, consisting of a single transistor and a capacitor. The figure below shows a simplest example of a DRAM cell consisting of a single NMOS transistor and a capacitor. The gate of the transistor is connected to a "row select" or "wordline", and the source of the transistor is connected to the "bitline". When both the wordline and the bitline are brought to high voltage, the transistor is on, and charge can flow to the capacitor. If the capacitor initially had no charge (stored zero), then charge  flows into the capacitor. If the capacitor initially is charged (stored one), then very little charge flows into the capacitor. To read an individual bit, the sensing circuitry measures the amount of charge that flows into the capacitor and determines whether it is zero or a one. The capacitor is then refreshed by either fully charging it or completely depleting it of charge, depending on which state it was initially. The write cycle simply charges a capacitor to the desired state 0 or 1 and the amount of charge needed is not measured.

How Flash memory works?
Flash memory has a grid of columns called bitline and rows called wordline with a cell that has two transistors at each intersection as shown in the following diagram.


Flash memory is a type of EEPROM chip. The figure below shows a cross section of a single cell of flash memory. In short, a capacitor is stacked on the top of a transistor. The lower electrode of the capacitor is also the gate electrode of the transistor and it is called floating gate, the upper electrode of the capacitor is called control gate and it is connected to the world line.

Read, Write and Erase
To erase the cells of a chip to change the cell value to a "0" requires Fowler-Nordheim tunneling. A negative electrical potential, usually -10-13 volts, is applied to the floating gate. The electrons stored in the floating gate are drained to the source side of the transistor. The electrons in the cells of a Flash memory chip can be returned to normal ("1") by the application of a strong electric field. Flash memory uses in-circuit wiring to apply the electric field to the entire chip, or to predetermined sections known as blocks. Flash memory works much faster than traditional EEPROMs because instead of erasing one byte at a time, it erases a block or the entire chip, and then rewrites it. The writing process is through channel hot electron injection. The control gate is applied with a voltage of 10-13 volts, the source line is grounded and the bitline is applied a voltage about 5 volts. The following table shows that the process of writing, erasing and reading.




Examples of Removable Flash memory cards:
Smart Media
Smart Media was originally developed by Toshiba. Smart Media cards are available in capacities ranging from 2 MB to 64 MB, with 128 MB cards coming soon.  Smart Mediacards are elegant in their simplicity. A plane electrode is connected to the Flash memorychip by bonding wires. The Flash memory chip, plane electrode and bonding wires are embedded in a resin using a technique called over molded thin package (OMTP). This allows everything to be integrated into a single package without the need for soldering. The OMTP module is glued to a base card to create the actual card. Power and data is carried by the electrode to the Flash memory chip when the card is inserted into a device. A notched corner indicates the power requirements of the Smart Mediacard. Looking at the card with the electrode facing up, if the notch is on the left side, the card needs 5 volts. If the notch is on the right side, it requires 3.3 volts. Smart Mediacards erase, write and read memory in small blocks (256 or 512 byte increments). This approach means that they are capable of fast, reliable performance while allowing you to specify what data you wish to keep.
Compact Flash
Compact Flash cards were developed by Sandisk in 1994, and they are different from Smart Media cards in two important ways: They are thicker, and they utilize a controller chip. Compact Flash consists of a small circuit board with Flash memory chips and a dedicated controller chip, all encased in a rugged shell that is several times thicker than a Smart Media card. Compact Flash cards support dual voltage and will operate at either 3.3 volts or 5 volts. The increased thickness of the card allows for greater storage capacity than Smart Media cards. Compact Flash sizes range from 8 MB to 192 MB. The onboard controller can increase performance, particularly on devices that have slow processors. The case and controller chip add size, weight and complexity to the Compact Flash card when compared to the Smart Media card.

Defect Detection
The basic idea of defect detection is to compare the light intensity level (gray level) for a candidate cell or die with two neighboring reference cell or die to see if there is any difference. If a difference is found to be above a certain threshold, then a defect is found. There are brightfield, darkfield and e-beam inspection technologies. Brightfield and darkfield are optical technologies, they can detect surface defects and defects in shallow trenches quickly. E-beam technology is used to detect sub-surface defects.
Darkfield inspection technology is the throughput leader among the three distinct inspection technologies. It uses a laser beam to illuminate the wafer surface at a low angle, thereby minimizing light scatter from the wafer surface and previous layers, and maximizing light scatter from defects and other anomalies. The noise suppression capabilities of darkfield technology enable high performance on CMP layers as well as rough and transparent films such as thin film deposition layers. The typical inspection tools are KLA-Tencor's AITx and Applied Materials' Excite . Excite tools are fast and ideal for tool monitoring.
Brightfield inspection systems use a focused beam of broadband light to illuminate the wafer. Different pixel sizes can be chosen to meet sensitivity and throughput requirements. This inspection technology is widely used for the etch layers. They can be used for array and random inspection. The typical tools are KLA-Tencor's KLA21xx .
E-beam inspection technologies measure reflected electrons. Electrons have much shorter wavelength than light, therefore the resolution of an e-beam inspection is much higher than optical systems. Furthermore, E-beam inspection systems are not gated by noise sources, such as grain noise, color noise and previous layer noise, that can inhibit optical inspection. The combination of high resolution and low noise allows e-beam systems to detect defect down to 50 nm in size. The e-beam technologies can image the bottom of high aspect ratio trenches and via holes and detect physical defects in these structures. Also e-beam inspection systems allow the detection of electrical failures within the device, using a technique called voltage contrast. Because electrons carry charge, they can be used in the production line to quickly detect defect mechanisms that cause electrical shorts and opens. The typical tool is KLA-Tencor's ES20XP .

Defect Review Tools:
Leica , JEOL , Semvision

Defect Control and Analysis Softwares:
Klarity Defect , Quest , HPL Yieldirector