Studies On Fully-Printed Read Only Memory Devices And Their System Applications

Current researches on solution-processed semiconductors,insulators,and conductive functional materials have given rise to the work on manufacturing various electronic devices by using conventional printing techniques.Compared to traditional silicon-based microelectronics,printed electronics technology can effectively reduce the manufacturing cost and energy consumption,simplify the manufacturing process and improve productivity.In addition the technology can be used with all commonly used substrate materials to produce light,flexible,low-cost and even rollable(stretchable)electronic devices.It is superior to traditional silicon-based microelectronics because of its compatibility with low heat tolerance materials such as plastic film and fiber paper.One of the basic data storage devices of printed electronics,the printed read-only memory device,exhibits the features of not losing data when power off and not rewrittenable during work.Thus it is of great importance for for large-area and flexible applications(smart packaging)and low-cost,disposable applications(logistics monitoring,security products)and could be use as a good complement for the current silicon based memories in respective fields.According to their data writing methods,the currently reported read only memory devices can be catogarized into process-writing type and electric-writing type.These two types have their respecitive device characteristics and application advantages but suffer form their own problems as well,which greatly hindle their development in practicality.Firstly,the most representative work of process-writing type,the polymer resistor memory,has its advantages of low manufacturing cost and multi-bits storage ability but has its drawback of poor stability caused by its sensitivity to surrounding environment.This drawback makes the polymer resistor memory not satisfiable to practical needs.Secondly,the fuse-type read only memory is the mostly stable and low-cost processible type in electric-programming category but it only has one-bit storage capacity with relatively large fuse current.These shortcomings are great obstacles for the application of fuse-type read only memory,expecially in flexilble and wearable applications.The key challenge of practical development for fully printed read only memory is to solve the representative problems in process-writing ROM and electric-writing ROM.Based on the discussion above,my research focus on the polymer resistor memory and electric-writing fuse-type read only memory.This paper proposed several new device structures and fabrication processes for printed read-only memory devices,as well as material improvements over existing devices in order to solve the key problems of practical use.And from the industrial point of view,the paper examined the device functionalities by developing two systems based on near field communication(NFC)and serial communication(UART)with integration of printed memory devices.The innovative outcome of my research mainly includes the following sections:Firstly,to solve the stability issues of polymer resistor read-only memory devices,the paper innovatively proposed the method to fabricate devices by neutral-pH PEDOT:PSS instead of conventional acidic PEDOT:PSS(PH1000)based on the detailed analysis of factors leading to instability.This kind of neutral-pH PEDOT: PSS ROM devices showed good stability under different test conditions such as being exposed in air environment,voltage bias,high temperature and high humidity.The devices fabricated by the proposed method have a more than 30 days retention time and can work normally after 20000 times of readout.Compared to the work reported before,the devices proposed in this paper have a great improvement in stability,which contributes to the practical development of this kind memory devices.Secondly,to achieve multi-bits storage for fuse-type read only memory,this paper has proposed an innovative structure by connecting resistor lines of different fuse voltage in parallel based on the property that resistor size could affect the fuse voltage.A fully printed multi-bits fuse type read only memory was firstly implemented using this structure.In addition the structure proposed in this paper can also be applied to other similar device fabrication based on fuse mechanism.This provides a beneficial exploration for the improvement of capacity in fuse-type read-only memory.Thirdly,to solve the big programming current issue of fuse-type memory device,this paper proposed a new fabrication method using silver nanowire bar coating to produce a write-once-read-many fuse-type read only memory device with both low writing current and writing voltage.The programming voltage of proposed device is found to be around 3V,while programming current can be as low as 1 mA,which is roughly 10 times smaller than currently reported devices.Besides,the proposed device also exhibits a high level of optical transparency,making its data extremely hard to decode through optical observation.This together with its multi-bit storage feature make this type of device ideal for industrial application.Lastly,to meed the need of product anti-counterfeiting and smart packaging,a wireless NFC data read system and UART data Read/Write system are designed.By building the systems integrated with the printed memories and verifying their functionalities,the paper further secured the excellent application promise for the printed read-only memory proposed by this paper.