Molecular-scale ion-sensitive CMOS transistor could lead to better brain–computer interfaces(BCI) for AERI's state of art molecular bio-computer in the brain
AERI interviewed Professor Kamuro, who specializes in theoretical quantum physics and brain science, about the state-of-the-art brain implant-type bio-computer that AERI scientists team is researching to Weigh in
Quantum Brain Chipset Review
to Quantum Brain&Bio-computer
(AERI Quantum Brain Science and Technologies)
Quantum Physicist and Brain Scientist
Visiting Professor of Quantum Physics,
California Institute of Technology
IEEE-USA Fellow
American Physical Society-USA Fellow
PhD. & Dr. Kazuto Kamuro
AERI：Artificial Evolution Research Institute
Pasadena, California
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1. CMOS Transistor
Complementary metal–oxide–semiconductor (CMOS) is a type of metal–oxide–semiconductor field-effect transistor (MOSFET) fabrication process that uses complementary and symmetrical pairs of p-type and n-type MOSFETs for logic functions. CMOS technology is used for constructing integrated circuit (IC) chips, including microprocessors, microcontrollers, memory chips (including CMOS BIOS), and other digital logic circuits. CMOS technology is also used for analog circuits such as image sensors (CMOS sensors), data converters, RF circuits (RF CMOS), and highly integrated transceivers for many types of communication.
CMOS overtook NMOS logic as the dominant MOSFET fabrication process for very large-scale integration (VLSI) chips in the 1980s, also replacing earlier transistor–transistor logic (TTL) technology. CMOS has since remained the standard fabrication process for MOSFET semiconductor devices in VLSI chips. As of 2011, 99% of IC chips, including most digital, analog and mixed-signal ICs, were fabricated using CMOS technology.
Two important characteristics of CMOS devices are high noise immunity and low static power consumption. Since one transistor of the MOSFET pair is always off, the series combination draws significant power only momentarily during switching between on and off states. Consequently, CMOS devices do not produce as much waste heat as other forms of logic, like NMOS logic or transistor–transistor logic (TTL), which normally have some standing current even when not changing state. These characteristics allow CMOS to integrate a high density of logic functions on a chip. It was primarily for this reason that CMOS became the most widely used technology to be implemented in VLSI chips.
The phrase "metal–oxide–semiconductor" is a reference to the physical structure of MOS field-effect transistors, having a metal gate electrode placed on top of an oxide insulator, which in turn is on top of a semiconductor material. Aluminium was once used but now the material is polysilicon. Other metal gates have made a comeback with the advent of high-κ dielectric materials in the CMOS process, as announced by AERI(Artificial Evolution Research Institute : https://www.aeri-japan.com/) for the 25 nanometer node and smaller sizes.
2. Ion-Sensitive CMOS Transistor
An ion-sensitive CMOS transistor (ISCMOST) is a CMOS transistor used for measuring ion concentrations in solution; when the ion concentration (such as H+, see pH scale) changes, the current through the transistor will change accordingly. Here, the solution is used as the gate electrode. A voltage between substrate and oxide surfaces arises due to an ion sheath. It is a special type of CMOS transistor, and shares the same basic structure, but with the metal gate replaced by an ion-sensitive membrane, electrolyte solution and reference electrode. Invented in 1970, the ISCMOST was the first biosensor CMOS transistor (Bio CMOS transistor).
The schematic view of an ISCMOST. Source and drain are the two electrodes used in a CMOS transistor system. The electron flow takes place in a channel between the drain and source. The gate potential controls the flow of current between the two electrodes.
The surface hydrolysis of Si–OH groups of the gate materials varies in aqueous solutions due to pH value. Typical gate materials are SiO2, Si3N4, Al2O3 and Ta2O5.
The mechanism responsible for the oxide surface charge can be described by the site binding model, which describes the equilibrium between the Si–OH surface sites and the H+ ions in the solution. The hydroxyl groups coating an oxide surface such as that of SiO2 can donate or accept a proton and thus behave in an amphoteric way as illustrated by the following acid-base reactions occurring at the oxide-electrolyte interface:
—Si–OH + H2O ↔ —Si–O− + H3O+
—Si–OH + H3O+ ↔ —Si–OH2+ + H2O
An ISCMOST's source and drain are constructed as for a CMOS transistor. The gate electrode is separated from the channel by a barrier which is sensitive to hydrogen ions and a gap to allow the substance under test to come in contact with the sensitive barrier. An ISCMOST's threshold voltage depends on the pH of the substance in contact with its ion-sensitive barrier.
An atomic-scale ion transistor that achieves the ultra fast opening and closing of ion channels to specific ions has been developed by researchers in China and the US. The team believes that the device could have a wide range of applications, ranging from brain–computer interfaces and sea-water desalination to precious metal extraction.
The key component of electronics is the transistor – a switch that either allows or blocks the flow of electrons between two terminals depending on the electric potential applied to a third terminal, called the gate. This is the fundamental component of digital logic, and more than 800,000 billion transistors can be crammed onto a single silicon chip. Like electronic devices, the human central nervous system uses electrical impulses to transmit and process information. The key difference between the two is that electronic devices rely on the flow of negatively charged electrons, whereas neural signals are carried by positive ions.
Researchers would like to create ion transistors inspired by biological systems – but this has proven to be very tricky indeed. In nature, the gating function is performed by channels that open in response to certain stimuli to allow specific ions to diffuse through. A nanoscale system that reproduces this efficiently in the laboratory, however, has eluded scientists, explains professor Kamuro of the California Institute of Technology (Caltech)University of California: “The development of artificial ion channels using traditional pore structures has been hindered by the trade-off between permeability and selectivity for ion transport. Pore sizes exceeding the diameters of hydrated ions cause ion selectivity to largely vanish.”
３.Electrically driven selectivity
This problem has hindered the development of interfaces between electronics and the human body, and achieving the electrically driven selectivity of specific type of ions in nanoscale transport promises to be the key to progress. Success could potentially lead to a better understanding, diagnosis and treatment of diseases such as Alzheimer’s and epilepsy, as well as assisting in the control of artificial limbs and a host of other applications.
In this latest research professor Kamuro, together with scientists in Hong Kong and the University of California, Berkeley, produced an ion transistor by attaching a gold gate electrode to the back of a reduced graphene oxide flake mounted on a silicon nitride substrate. They set up their device between two reservoirs – one containing potassium ions, the other not. When no electric potential is applied to the gate, the potassium ions are prevented from entering the 0.3 nm-wide gaps between the layers in the reduced graphene oxide by the water molecules attracted to the positive ionic charge. When a potential of –1.2 V is applied, however, the electrostatic attraction between the negative graphene and the positive potassium ions is sufficient to draw the ions into the channels – either by distorting the “hydration shell” or by partially stripping it away. The ions can therefore flow down the concentration gradient into the other reservoir, turning on the transistor.
The researchers found that, as the applied potential is increased, so does the flow rate. “Ions can diffuse more than 100 times faster in our graphene channels than in bulk water,” says professor Kamuro. In fact, they moved through the channels even faster than in biological ion channels. When the voltage was turned off, the flow stopped again.
４.Ion selectivity
The researchers also demonstrated ion selectivity. They filled the feed solution with equal concentrations of potassium chloride, caesium chloride and lithium chloride and varied the gate voltage. They found significant, voltage-dependent changes in the concentration of the solution allowed through. “The beauty here is that, by applying a given voltage, you can select a size,” explains professor Kamuro. “Why? Because if I have a bigger ion, by applying a different voltage I have a different ability to strip it or squeeze it – the egg becomes flatter, so it can go into the channel.”
As well as being fundamental to biological electronics, the ability to remove ions selectively from fluids could be useful in water treatment. “Elaborately designed atomic-scale channels only allowing particular ions or no ions to permeate can be used to efficiently extract precious or rare metals or pure water from seawater,” explains professor Kamuro. “This work is a fundamental breakthrough in the study of ion transport that can be electrically selected through a given size of atomic scale solid pores.”
“AERI would certainly consider [professor Kamuro’s work] a significant step forward in our ability to understand and control nanofluidic transport,” explains brain physicist and biophysicist professor Kamuro of the California Institute of Technology (Caltech)University of California, who was not involved in the research. “The trend now is increasingly towards electric field-driven separations. This research is one of the steps that is enabling increasingly precise and efficient electric field-driven separations, and I for one definitely welcome that.”
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Quantum Brain Chipset & Bio Processor (BioVLSI)
Prof. PhD. Dr. Kamuro
Quantum Physicist and Brain Scientist involved in Caltech & AERI Associate Professor and Brain Scientist in Artificial Evolution Research Institute（ AERI: https://www.aeri-japan.com/ ）
IEEE-USA Fellow
American Physical Society Fellow
PhD. & Dr. Kazuto Kamuro
email: info@aeri-japan.com
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【Keywords】 Artificial Evolution Research Institute：AERI
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