ABSTRACT:

This paper presents the thin film film film technology –printed printed rewritable memory in electronics. Polymer This is currently the subject of a great deal of scientific investigation and development. This interest can be attributed to the low cost, easy processing steps and simple device structures of electronics when compared to conventional silicon and inorganic electronics. In the fieldfs of electronics memories nonvolatile, rewritable polymer memory devices (PMDs) have shown promise as a future technology where cost and compatibility with flexible substrates are important factors.

.Using printing to manufacture electronic memory makes it possible to reduce the number of process steps, resulting in dramatically lower manufacturing costs, and also reduced environmental impact as compared to traditional semiconductor processes. Commercial applications of printed electronics include e-

paper, electronic readers, and organic light emitting (OLED) displays. Sensors, batteries,and photovoltaic energy sources are also in development, and together with Thinfilm's memory technology they will open the door to new products and applications, for example, in the field of RFID systems .

Memory is an essential part of most electronics. Memory is required for identification, tracking status, and history, and is used whenever information is stored. Thinfilm's non-volatile ferroelectric polymer memory technology is well suited for application with other printed electronics devices because power consumption during read and write is negligible, and as the memory is permanent, no connection to

external power is required for data detainment. Also, the electric current required to write information is so small that operation would be limited by the battery's lifetime and not its capacity.

"As a manufacturing method printing brings many benefits including processing over large areas at high speed or over curved surfaces. Using an additive method which places the material only where it is required greatly reduces the number of steps needed compared with a subtractive method where the material is deposited everywhere and then etched back into the required pattern. Printing also readily allows digital methods to be used (such as ink-jet), so that new layouts can be created directly from the design, enabling rapid prototyping and facile customization. Furthermore, printing should also enable manufacturing sites to be set up at a fraction of the cost of conventional

semiconductor fabrication lines, allowing smaller, more diverse organizations to be involved in the manufacture of electronic components."

"Printing enables low-cost advantages and novel form factors not easily attained by other electronics-manufacturing methods. The applications, from consumer electronics to biomedical devices, are endless. A great deal of progress has been made recently in printed electronics, but we are unable to see printed devices around us everyday, everywhere electronic .memory devices are currently receiving an unprecedented amount attention as possible alternatives for conventional semiconductor memories, due to their simple device structures, ease of fabrication, compatibility with flexible substrates and low cost. Thinfilm’s unique all-printed re-writable products are ideal for use in standalone consumer applications, including personalized toys and online-enabled games. They can also be integrated with logic elements, sensors,

batteries, and displays for mass market applications such as all-printed RFID tags. The proven high volume roll-to-roll production of Thinfilm printed memories provides the platform for its Memory Everywhere vision.

1.INTRODUCTION:

A thin film is a layer of material ranging from fractions of a nanometer (monolayer) to several micrometers in thickness. A familiar application of thin films is the household mirror, which typically has a thin metal coating on the back of a sheet of glass to form a reflective interface. The process of silvering was once commonly used to produce mirrors. A vey thin film coating (less than a nanometre thick) is used to produce two-way mirrors.

The various thin-film technology(TFT) currently

being developed reduce the amount (or mass) of light absorbing material required in creating a solar cell. This can lead to reduced processing costs from that of bulk materials (in the case of silicon thin films) but also tends to reduce energy conversion efficiency,

although many multi-layer above those of bulk silicon wafers. Thin-film cells offer advantages beyond cost, including pliability, and potential integration with preexisting buildings and infrastructure.

Thin film memory consists of a ferromagnetic material, permalloy, deposited (under controlled conditions in a vacuum chamber) on a substrate of thin glass. After all air has been removed from the chamber, a shutter arrangement is opened

and vapors from molten permalloy pass through a mask and are deposited on the substrate. The pattern thus formed is determined by the shape of the mask. The thickness of each spot (magnetized area) is controlled by the amount of time the shutter' is open.the printed logic must be integrated with memory. The programmable logic module

could then be programmed

to be used for controlling a

display, handling in and

output from a sensor,

playing a little tune etc.

Thinfilm is actively

cooperating with partners

such as PolyIC and Soligie

to achieve programmable

logic blocks. 2.Thinfilm

Technology :

Thinfilm’s technology is

based on using a

ferroelectric polymer as the

functional memory

material sandwiched

between two sets of

electrodes in a passive

matrix – each crossing of

metal lines defines a

memory cell.

The memory function is based on an intrinsic mechanism related to orientation of the polymer chains. The polymer chains can be oriented in two different ways representing “0” and “1”. Each state is stable without application of an external field which means that information in the memory will not be lost when the power is turned off.  This is referred to as a non-volatile memory. The intrinsic character of the polymer means that the technology is extremely scalable. Thinfilm has demonstrated 110 nm cells and shown that no lower limits could be found. An additional important characteristic of the technology is that it is based on non-toxic materials. This is very important in realizing our Memory Everywhere vision

The Thinfilm-patented passive matrix is the “Holy grail” of memory architectures that dispenses

with the need of active circuitry within the memory cell. This enables ultimate packing for high density memories as well as the possibility to stack memory layers on top of each other. The passive array memory architecture allows the memory portion to be separate from the read/write electronics enabling stand alone application without integration with printed logic.

The core of Thinfilms know-how and patent portfolio relates to processing and design of memories and pulse protocols for practical application of  passive matrix architectures.  The main challenge in a passive matrix is related to reading and writing data of any

given cell without destroying/disturbing data stored in neighboring cells.

3.The Thin Film Process:Thin film process starts with an alumina ceramic substrate. A glaze pattern is then placed on the substrate to form a mound of glass beneath the location of the heater line.

An extremely thin layer of resistor material is then deposited on the entire surface of the substrate, followed by a thin layer of metal. Both of these layers are considered to be "thin film." These thin films are deposited by sputtering or by chemical vapor deposition. Diagram 1 below shows these layers covered by yet another layer, the photoresist. Next, the photoresist light-sensitive material is exposed in the first masking process and developed. Then portions of the thin films are etched away, resulting in a pattern of metal conductors, as shown in diagram 2.

(Figure

A second photolithographic process is used with the heater mask to etch away only the metal layer in a straight line across the conductor patterns over the glaze mound, exposing a line of thin-film high-

resistance heater elements. The heater elements and the adjacent portions of the metal conductors are then covered by another thin film of abrasion-resistant ceramic coating, which is thin enough to efficiently conduct heat into the thermal paper or thermal transfer ribbon that is pressed against it.

4.Storage:

Thin film materials are well suited for storing binary data since they have a stable state of magnetization in each direction parallel to the preferred axis. The double-headed arrow in the circle shown in figure 6-17A is to be regarded as indicating the preferred axis. When the direction of magnetization is caused to rotate through 180 degrees (starting from the preferred axis), there is first a torque which tries to retain the magnetism along the preferred axis. If the magnetizing force is sufficiently strong, the magnetism will be shifted to a point perpendicular to the preferred axis. Beyond this point, there is a forward torque which causes the magnetism to be alined in the material exactly 180° from the preferred axis. The torque is caused by the field HK which is produced during the deposition process. This field is called the anisotropic field.

If the magnetic stimulus is removed after the anisotropic field is formed, this field (HK) causes the magnetic vector to be alined parallel to the preferred axis. If a coercive force, HC, which

is less than that required to switch the

magnetization but produces a field parallel to the preferred axis is applied, no significant change results in the state of the magnetized material.

Applying only a transverse field, HT, (fig. 6-17B), i.e., a magnetic field perpendicular to the preferred axis, and which is stronger than HK, causes the magnetic state of the spot to be rotated 90° as shown in figure 6-17C. If fields are applied so that the vector sum of HL + HK is an active force on the spot, the position of the resultant magnetic vector will be as illustrated in figure 6-17D. If HT is then removed from the spot, the direction of the magnetization be- comes the same as that for HL. When HL is removed, the spot remains in the new state until HT is again applied. Thus, the direction of HL determines the direction of the stable state of magnetization of the film spot.

5.SENSING :

The thin-film memory is a destructive readout memory; i.e., the reading of thin film spot (location) clears the contents of that address. During a readout, all of the addressed spots are switched toward the "0" state. The sharp change in the magnetic field around any spot causes a voltage to be induced in the sense lines. The magnitude of this voltage depends upon the change in the magnetic flux resulting from the switching process.

The output is read from the memory by ANDing a strobe pulse with the output from a sense amplifier (not shown) whenever a 1 is stored in the location being read. No output from the AND circuit indicates a "0" has been read. Figure 6-19 illustrates the timing relationships during readout.

6.Printed non-volatile rewritable ferro-electric memories:

Printed electronics has recently moved from a focus on the production of individual components towards the design and initial commercialization of integrated systems.  To

create such systems, the use of non-volatile random access memory is often essential. This article describes the function and design of Thinfilm memories based on a reversible ferro-electric capacitor structure, and their application to novel products and markets.

7.Basic memory cell:A  Thinfilm memory cell consists of a ferroelectric polymer sandwiched between two electrodes, denoted arbitrarily as a bit line (BL) and a word line (WL). On the application of a sufficient voltage, the dielectric dipoles within the polymer layer

align, and because of hysteresis when the voltage is removed, the dipoles remain pinned in the state they had during the voltage pulse.This is depicted in the curve in figure 1a. As the voltage can either be polled in a positive or negative direction, the dipoles can align in two separate directions.  The ferro-electric capacitor cell is thus bistable and by applying a proper voltage pulse it can be ‘written’ into two different stable states. As is indicated in figure 1, the 0-state is defined to be on the top of the hysteresis curve, when the x-axis is the BL voltage minus the WL voltage, while the 1-state is at the bottom.

Figure 1 a) Hysteresis curve, b) ferro-electric connected to a charge integrator and c). 0-signals and 1-signals from 5500 R2R produced cells.

The electrode chosen as the BL is connected to a sense amplifier which detects the cell state. Using charge integrator circuitry (Fig.1b), the sense amp outputs a voltage proportional to the amount of charge released from the cell when the read voltage pulse is applied. As can be seen in the hysteresis curve, reading a cell in the 0-state gives a larger charge release

compared to reading a 1-state cell. Figure 1c shows sampled charge integrator outputs, converted to polarization from 5500 memory cells. The red dots show the polarization (uC/cm2) measured when the cell is written into a 0-state before measurement, while blue dots correspond to readings from the same cells written with 1-state signals. As can be seen, there is a large difference in output signals, and use of a suitable threshold allows for identification of the data content of the memory cell.

The green curves show the resistive leakage of the cells, and contribute insignificantly to the polarization measured from the 0-state.  That means that the signal-to-noise ratio is very good, and this holds for a large range of environmental conditions and is not affected by using

printing as the manufacturing process.

8.Thinfilm Printed CMOS Memory :

Combination of Thinfilm Printed Rewritable Memory and PARC Transistors Enables Low-Cost, Printed Integrated Systems for the "Internet of things"

The world's first printed non-volatile memory device addressed with complementary organic circuits, the organic equivalent of CMOS

circuitry. Thinfilm Addressable Memory consists of Thinfilm's printed memory and PARC's transistors.

Thinfilm Addressable Memory combines Thinfilm's polymer-based memory technology with PARC's transistor technology using complementary pairs of n-type and p-type transistors to construct the circuits. The addition of the integrated circuits makes the roll-to-roll printed Thinfilm Memory addressable by printable logic.

The demonstration of Thinfilm's Addressable Memory is a significant step toward the vision of a world filled with the "Internet of things", where everything is connected via a smart tag. These smart tags require the commercial availability of devices that:• have rewritable memory,• are low cost,• support integration with sensors and other electronic components, • are environmentally friendly,• and can be produced

using high volume, roll-to-roll printing.

The demonstrated prototype, rewritable memory with logic circuitry, will meet all of these requirements.

These systems will benefit from Thinfilm's unique non-volatile ferroelectric polymer memory technology because power consumption is negligible and no connection to external power is required to retain information.

"We have demonstrated that one can address an array of memory cells using printed logic. This opens up new fields of use, as now addressable memory can be combined with sensors, power sources and antennas to power smart applications," . "This prototype is a demonstration that low-cost printed integrated systems and the tagging of everyday objects is possible, enabling

Thinfilm's vision of ‘memory everywhere'."

System products are integrated systems that combine Thinfilm's memory technology with other printed components. The target markets for Thinfilm Addressable Memory system products include NFC (Near Field Communications) tags, now available in Android phones, which enable device to device communication and have been predicted to, one day, be on all new objects. Thinfilm also targets sensor tags and disposable price labels. The addressable memory can be integrated with other printed components, such as antennas and sensors, to create fully printed systems for interaction with everyday objects .

Using printing to manufacture electronics minimizes the number of process steps, which in turn, dramatically

reduces manufacturing costs and lowers the environmental impact compared to traditional semiconductor processes. Thinfilm devices are thinner than traditional silicon devices and can be produced in form factors as slim as a strand of hair.

9.Advantages:

Thinfilm Electronics has developed a non-volatile, rewritable printed memory that is commercially available in the form of stickers that can be attached to cards, toys, and other flat or smoothly curved surfaces Thinfilm memories are much more cost-effective and environmentally friendly due to the use of an additive process and less-costly deposition methods other applications of printed electronics include printed solar cells and organic light emitting diodes (OLED) for lighting and displays.

Sensors, batteries and photovoltaic energy sources are also in the market or under development. With continuing advances in device design, materials and manufacturing processes, devices like Thinfilm’s memory technology will open the door to new products and applications Low-cost, flexible devices that have the capability to both store data locally and communicate with the infrastructure around them will be critical to enabling many different visions for “the Internet of things.”

Conclusion: