Implantable transient memory will play a significant role in the field of RFID electronic tags

2024-01-15

Recently, the scientific research team of the Chinese Academy of Sciences Shanghai Institute of Microsystems and Information Technology published a paper entitled "A Hierarchically Encoded Data Storage Device with Controlled Transiency" in the magazine Advanced Materials, which innovatively developed a multi-level implantable transient memory based on silk protein, making breakthroughs in memory mechanism, materials and structure. Transient soluble memory is an important component and information storage medium in transient soluble electronic implantation devices. This memory needs to have stable storage and encryption functions while achieving controllable degradation.

This memory adopts a brand new memory structure, which optimizes the vertical high-density integration of three different types of information storage units: resistive variable memory resistors, terahertz metamaterials, and optical diffraction elements through process optimization, achieving synchronous and stable storage of electrical, electromagnetic, and optical information on a single device. A memory material system composed of silk protein with adjustable dissolution characteristics and degradable metals (magnesium, aluminum) ensures that each layer of storage unit has good electrical and optical properties, and enables the memory to have multiple controllable degradation modes such as gradual layer by layer degradation, multi-layer rapid degradation, and controllable layer number degradation in selected areas. The combination of multimodal information encoding and multiple degradation modes greatly enhances the encryption ability and information storage capacity of transient memory, with only 16 units capable of storing information of the order of 1055 bits; 4 prepared × The 4-array transient soluble memory prototype has implemented alphabet encoding, 16 bit binary encoding demonstration, and verification encoding and decoding examples. Thanks to the uniform film formation and precise controllable degradation ability of silk protein, the low misreading rate and strong robustness of memory information meet the requirements of multimodal information storage and high stability storage. The subcutaneous implantation experiment in mice further verified the feasibility and biosafety of the transient memory's layer by layer degradation in vivo.

Silk protein with excellent biocompatibility does not cause tissue immune response, indicating that the new multi-layer transient soluble memory will play an important role in implantable devices and chips, in vivo information storage, and bioelectronic tags.

The Relationship between RFID Electronic Labels and Memory

The level of RFID electronic tags is closely related to the structure of the memory. Due to differences in memory, electronic tags are divided into read-only electronic tags, writable electronic tags, electronic tags with password function, and segmented storage electronic tags. Among them, read-only electronic tags have the lowest level, while electronic tags with password function and segmented storage have a higher level.

1、 Read only electronic tags

During the recognition process, only electronic tags that can be read but not written are read-only electronic tags. The memory possessed by read-only electronic tags is read-only memory.

When the RFID electronic tag enters the working range of the reader, the electronic tag begins to output its feature marks. Usually, chip manufacturers ensure that each electronic tag is assigned a unique serial number. The communication between electronic tags and RFID readers can only be carried out in one direction, that is, RFID electronic tags continuously send their own data to RFID readers, but readers cannot transmit data to electronic tags. This type of electronic tag has simple functions, simple structure, and low price, making it suitable for use in price sensitive situations. Read only electronic tags are mainly used in animal recognition, vehicle access control, temperature and humidity data reading, and industrial data centralized control.

It is worth mentioning that read-only electronic tags can also be divided into the following three types:

(1) Read Only Label

The content of a read-only label is already written when the label leaves the factory, and can only be read and not written again during recognition. Memory with read-only tags is generally composed of ROMs.

The data stored in ROM is usually pre written before being loaded into the entire machine. During the operation of the machine, it can only be read out, unlike random access memory, which can be quickly and conveniently rewritten. The data stored in ROM is stable and does not change even after power failure. Its structure is relatively simple and easy to read, so it is often used to store various fixed programs and data. The feature markers of read-only electronic tags are generally represented by serial numbers, which have been solidified during the chip production process, and users cannot change any data on the chip.

(2) One time programming read-only label

One Time Programmable (OTP) read-only tags can be programmed and written in one go before the application, and cannot be rewritten during the recognition process. The memory for one-time programming read-only tags is generally composed of PROMs.

(3) Repeatable programmable read-only label

The content of a programmable read-only tag can be erased and written repeatedly, but cannot be rewritten during the recognition process. Memory with programmable read-only tags is generally composed of EEPROMs.

2、 Writable electronic tag

During the recognition process, RFID electronic tags with both readable and writable content are called writable electronic tags. Writable electronic tags can use SRAM or FRAM memory.

Static Random Access Memory (SRAM) is a type of memory with static access capabilities. SRAM can save the data stored internally without refreshing the circuit, thus SRAM has high performance.

Ferroelectric Memory (FRAM) is a non-volatile random access memory that provides performance consistent with RAM, but also has the same non-volatile properties as ROM. FRAM non-volatile refers to the technology that does not lose data after a memory power outage, and non-volatile memory is derived from ROM. FRAM combines the non-volatile data storage characteristics of ROM with the advantages of unlimited read and write, high-speed read and write, and low power consumption of RAM, which enables FRAM products to perform both non-volatile data storage and operate like RAM.

When working with a writable electronic tag, RFID read-write devices can write data into the RFID electronic tag. The writing and reading of electronic tags are mostly carried out in word groups, which are usually a collection of a specified number of bytes. Word groups are generally read or written as a whole. In order to modify the content of a data block, it is necessary to read the entire data block from the RFID reader, modify it, and then re read the data as a whole.

The storage capacity of writable human style electronic tags can be at least 1B and up to 64KB. A typical electronic tag is 16 bits, ranging from tens to hundreds of bytes.

3、 Electronic tags with password function

For writable electronic tags, if there is no password function, any reader can read and write data to RFID electronic tags. To ensure the security of system data, unauthorized access to electronic tags should be prevented. This allows for various methods to protect RFID electronic tags. The protection of RFID tags involves data encryption, which can prevent tracking, theft, or malicious tampering with the information of electronic tags, thereby ensuring the security of data.

(1) Graded key

A graded key refers to a system that has multiple keys, each with different access permissions. In applications, the level of the key can be determined based on the access permissions. For example, a certain system has keys A and B, and the authentication between RFID electronic tags and RF readers can be determined by keys A and B, but the levels of keys A and B are different.

The data inside the electronic tag is divided into two parts, protected by key A and key B. The data protected by key A is stored in read-only memory and can only be read out, not written. The data protected by key B can be written into memory storage, and reader 1 has key A. After successful electronic tag authentication, reader 1 is allowed to access the data protected by key A. Reader 2 has key B. After successful electronic tag authentication, reader 2 is allowed to read the data protected by key B and write the data in both directions.

(2) The application of hierarchical keys in public transportation

In urban public transportation systems, there are application examples of hierarchical keys. Nowadays, urban public transportation systems can use card swiping devices (readers and writers) for boarding, as well as readers and writers used by bus companies to recharge cards.

The card swiping for public transportation adopts a close contact card swiping method, and the amount is deducted from the card for each swiping. This part of the data is stored on the card. There are two types of readers and writers for urban public transportation systems, one is key A authentication on public buses. RFID electronic tags can also be recharged, which is authenticated by key B. The reader on the bus only has key A. After the electronic tag authentication key A is successful, the reader on the bus is allowed to deduct the amount on the electronic tag.

The reader of the bus company has key B. The electronic tag needs to be recharged by the bus company. After the electronic tag authentication key B is successful, the bus company's reader/writer is allowed to recharge the electronic tag.

4、 Segmented storage of electronic tags

When the storage capacity of electronic tags is large, the storage of electronic tags can be divided into multiple storage segments. Each storage segment unit has independent functions and stores independent data for different applications. Each storage segment unit has separate key protection to prevent illegal access.

Generally speaking, a reader/writer only has a key for one storage segment of the electronic tag, and can only obtain access to a certain application of the electronic tag. A certain electronic tag has multiple functions such as car departure, community payment, car refueling, and retail payment. Different types of data have their own keys; A reader usually only has one key (such as a car entry and exit key) and can only be accessed within that storage segment (such as charging for car entry and exit).

To achieve low-cost electronic tags, the storage segments of electronic tags are generally set to fixed sizes, which is relatively simple to implement. Electronic tags with variable length storage segments can better utilize storage space, but implementation is difficult and generally rarely used. The storage segments of electronic tags can only be used in part, while the remaining storage segments can be left unused.

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