As tiny as a speck of dust and injected with a needle, how was the "world's smallest single-chip system" created?
Latest update time：2021-09-08 11:25
Reads：
In the future, it may be possible to implant the chip into the human body through a needle injection to reduce
the damage caused to the body during the transplantation process.
Author | Wu You
Editor | Liu Xiaokun
In the future world described in the British TV series "Black Mirror", a smart chip is implanted behind the ear of every member of society. External instruments can store and retrieve memories in the mind through this chip, and can play and review the scenes in the memory at any time.
The human body implantation of smart chips in movies and TV shows seems very far away, but in fact, we have already seen signs of it in the real world.
In May this year, a research team from Columbia University published the research results of an implantable chip in top journals and international conferences such as Science Advances and IEEE International Electron Devices Meeting (IEDM), making new progress in miniaturized medical devices.
The team has developed a fully integrated implantable micro-sensor chip the size of a speck of dust, which can be used to monitor physiological signals by obtaining energy and transmitting data wirelessly through ultrasound.
Wikipedia calls it "the world's smallest single-chip system", setting a record for the smallest size of similar biochips. This means that in the future it may be possible to implant the chip into the human body through a needle injection, reducing the damage caused to the body during the transplant process.
Photo of the chip placed in a needle, showing its tiny size and injectable nature
So, how was this "world's smallest single-chip system" created? Recently, AI Technology Review had the honor of having a conversation with Shi Chen, the first author of the research project, to learn more about the secrets and details behind this micro sensor chip.
1
Using the "chip as system" approach to make medical instruments
Dr. Shi Chen graduated from Columbia University's Department of Electrical Engineering, where he studied under Professor Kenneth L. Shepard, a pioneer in the field of bioelectronics.
"During my doctoral studies, my advisor and I focused on the field of implantable medical devices. Although there are already many instruments that can play a role in the diagnosis and treatment of diseases, these instruments are relatively large in size. Even the smallest medical device is only the size of a grain of rice. They are often implanted into the human body through surgery, which is bound to cause a certain degree of trauma. Therefore, we hope to reduce the rejection reaction by reducing the size of medical devices and achieve non-invasive minimally invasive transplantation." He said when talking about the original intention of deciding to conduct this research.
In fact, after a period of development, implantable medical devices have formed multiple branches, including cardiovascular, orthopedic, neurological and other sub-tracks. There are both devices that replace human organs and instruments used for disease diagnosis.
"We want to explore the size limit of implantable medical devices. Chips, or integrated circuits, integrate various circuit components onto a tiny silicon chip. On this basis, we further integrate sensors, transducers, discrete circuit components and other components that are usually independent of the chip onto the chip, making the chip itself a complete system - "chip as a system", minimizing the size while ensuring certain functions. To prove this idea, we chose temperature measurement, which is more common in medical testing."
It should be noted that although in vitro temperature measurement is very mature, the measurement of the core temperature of the body, which has important medical significance, is still not easy to obtain.
After years of experiments and research, the team finally realized the dream of miniaturized medical instruments. The sensor chip they developed is only 0.065 cubic millimeters in size and can be injected into the body with a needle to monitor the core temperature of the body in real time.
Comparison photo of chip and one cent coin
This micro sensor chip mainly consists of two parts. One part is the piezoelectric material used as an ultrasonic transducer, which can convert sound energy into electrical energy. The other part is a temperature sensor chip used to collect ultrasonic energy and measure body temperature.
The temperature sensor chip designed by Shi Chen uses a 180nm process and is produced at TSMC. After receiving the sensor chip, he directly integrates a micro piezoelectric material on the surface of the chip based on a self-developed micro-manufacturing process without using any external circuit components or wires, thus realizing the concept of "chip as system" and extremely small size.
Unlike traditional chips, implantable chips also need to ensure the harmonious coexistence of the chip and the organism. Therefore, this small single-chip system must be encapsulated with a layer of thin film material that will not cause harm to the organism before it can be considered a complete implantable chip.
2
Ultrasonic waves enable wireless power supply and data transmission
How does this micro sensor chip monitor physiological signals wirelessly? In daily life, common wireless power supply and communication are achieved by radio frequency technology based on electromagnetic waves. However, the wavelength of electromagnetic waves is long, making it difficult to power such a small chip.
"Since the speed of sound is much smaller than the speed of light, ultrasound of the same frequency is much smaller than the wavelength of electromagnetic waves and is easier to match the size of this sensor chip. Therefore, we chose ultrasound to wirelessly transmit energy and data. At the same time, within a certain energy range, ultrasound is harmless to the human body," said Shi Chen.
In fact, ultrasound is now widely used in the medical field, and B-ultrasound is one of the most well-known medical applications.
Ultrasound image of the chip placed in the chicken, showing how the chip is located by B-ultrasound
"When the piezoelectric material receives ultrasonic energy, electric charges will be generated on the surface. The accumulated charges are converted from alternating current to stable direct current through the rectification circuit and voltage stabilization circuit inside the chip, thereby driving the entire temperature sensor. The temperature sensor consists of an oscillation circuit. Through certain designs, we make the oscillation frequency faster as the temperature is higher, and slower as the temperature is lower. The output of this oscillation circuit modulates the acoustic impedance of the piezoelectric material through a transistor, causing the amplitude of the ultrasonic wave reflected back from the piezoelectric material to change to a certain extent, and the frequency of the change is the output frequency of the temperature sensor. By observing the amplitude change of the reflected wave, the temperature signal can be obtained, realizing the wireless transmission and monitoring of temperature data."
3
Next step: Even smaller implantable chips
and More diversified physiological signal monitoring
Although a breakthrough has been made, Shi Chen also admitted that there is still a lot of room for improvement in the project:
The piezoelectric material used is unidirectional, which means that if the chip rotates inside the organism, the ultrasound cannot be transmitted vertically to the chip and the energy conversion efficiency will be reduced.
Injecting into the body is an easy task, but the team has not yet done more research on how to remove the chip. However, they believe there are two research paths: one is to excrete it through the normal metabolism of the organism, and the other is that the chip is small enough to be swallowed by cells.
In addition, the project is still in the laboratory stage and has only been tested on mice. It is not ruled out that new problems will arise when it is implanted in the human body.
There will be more possibilities for this project in the future. The long-term goal is to be able to measure more physiological signals in a smaller volume, including but not limited to pH value, blood pressure, blood sugar content, etc. There are
still many problems to be solved in the process of achieving this goal - how to find a better piezoelectric material to reduce the impact of ultrasound attenuation during propagation in the body; how to further reduce the chip size and power consumption, so that the chip can be implanted deeper and narrower in the body...
“These issues seem to check and balance each other, but that’s the beauty of research.”
Shi Chen, the first author of the project, presents the research results
Shi Chen graduated from the University of Washington with a double degree in bioengineering and electrical engineering. He has been interested in biology since he was a child, and chose to further study the intersection of biology and electronics. While studying for a doctorate at Columbia University, he also participated in projects such as brain-computer interfaces and neuromodulatory chips. Looking to the future, he hopes to continue to delve deeper into the field of bioelectronics and develop micro-medical instruments that can be truly clinically applied, providing patients with safer and more convenient monitoring and analysis of physiological signals for disease diagnosis and rehabilitation.
This article is originally written by Leifeng.com, author: Wu You
, editor: Liu Xiaokun
.
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