Basic gate stack structure of the Ferroelectric FET is Metal-ferroelectric-insulator-silicon (MFIS), where the memory window (M.W) is 2 & lowast; (P-r-Q it) /C-FE considering the trapped charge. However, in Metal - insulator - ferroelectric - insulator - silicon (MIFIS) gate-stacked FeFETs, the M.W is 2 & lowast; {(P-r-Q (it)) /C-FE+ (Q'(it)-Q (it)) /C G. IL) }, which allows the M.W to widen in case the Q'it injected from the gate side is larger than the Qit injected from the channel side. In this letter, we propose a band engineered (BE) gate insulator in MIFIS gate-stacked FeFETs. This lowers the energy barrier of the hole when applying the program voltage, thereby increasing the amount of hole injected from the gate side, and consequently widening the M.W. Furthermore, it is demonstrated by TCAD simulation that the physical origins of Vt shift of PGM state is hole injection. In addition, in the case of BE-MIFIS gate-stacked FeFETs, the maximum ISPP slope is increased by about 2 times compared to conventional MIFIS, which is an important feature in ferroelectric VNAND (FeVNAND) operated at low voltage.

For the first time, we demonstrate an in-depth analysis on a novel multi-layered gate-interfacial-layer (G.IL) and high-k channel-interfacial-layer (Ch.IL) in metal-insulator-ferroelectric-insulator-silicon (MIFIS) gate stack FeFETs, using simulations and experimental validation. By exploring materials with varying energy barrier heights between the gate metal and G.IL to control the tunneling of charges from gate, we demonstrate an optimal gate stack incorporating a high-k Ch.IL. Our findings underline the benefits of this configuration, including a larger memory window (MW) and improved reliability characteristics (especially disturb and retention characteristics).

Read-After-Write-Delay (RAWD) is an important show-stopper (S.S) in ferroelectric based VNAND (Fe-VNAND) because the read speed is fundamentally limited by neutralization time of trapped charges between the ferroelectric layer and the interfacial oxide layer. We investigated the RAWD time (t RAWD ) in Metal-Ferro-Insulator-Silicon (MFIS) gate stack and extended the analysis to Laminate-MFIS (LaMFIS), which are candidate for achieving higher memory window (M.W) in Fe-VNAND. After applying a positive voltage to MFIS and LaMFIS, it was confirmed that it takes about ‘1 second’ for the normal state, low threshold voltage (LVT), which is caused by excessively injected electrons from the channel. What is unusual in LaMFIS is that V t decreases further after about '10 seconds', which is caused by electrons deeply trapped in the inserted layer between the ferroelectric layers. In LaMFIS, there is a phenomenon in which V t rises slightly at low voltage of Incremental Step Positive Pulse (ISPP) operation. This is related to accumulation of deeply trapped electrons. The newly devised novel ISPP successfully removed these electrons and improve device speed and ISPP variation. Lastly, the RAWD of Metal-Insulator-Ferro-Insulator-Silicon (MIFIS) gate stacks, another candidate for achieving high M.W was analyzed.

Multibridge channel-ferroelectric field-effect transistor (MBC-FeFET) with metal-ferroelectric-metal-insulator-silicon (MFMIS) gate-stack is an advanced noble memory device, which is compatible with a 3-nm node technology logic device. Thanks to the wide effective channel width of the device's stacked nanosheet (NS), the capacitance ratio of the interfacial layer (IL) and ferroelectric layer ( C-IL / C-FE ) can be maximized without area penalty, significantly improving memory window (MW) and endurance characteristics. In this work, we developed analytical compact models of memory characteristics for MFMIS gate-stack-based MBC-FeFET. Also, using this model, the gate-stack design guidelines were presented. As a result, the MW becomes three times larger, and the electric field in the IL layer ( E-IL ) becomes 0.17 times smaller after optimization. This is 21 times larger MW compared to a planar FeFET with initial gate-stack parameters applied.

In ferroelectric FETs (FeFETs), the transient characteristics is a key issue to be addressed. Therefore, it is important to have an understanding based on accurate measurements of transient characteristics. In this work, the in-situ threshold voltage (V t ) measurement method is presented, which allows simultaneous observation of the change of remnant polarization (P r ) and V t over delay time within a device. This provides insight into the characteristics of both P r and trapped charge depending on delay time (t delay ). The transient characteristic after applying the positive voltage is particularly important, as electrons are injected from the channel side. Thus, we show that the time to a steady state of program V t is shortened by controlling the electrons by applying a small negative voltage immediately after the positive voltage.

In this study, we have demonstrated 3-Dimensional Stacked FET (3DSFET) with Self-Aligned Direct Back-side Contact (SA-DBC) and Back-side Gate Contact (BGC) in 48nm gate pitch, which is the smallest dimension and the world's first demonstration reported so far. Simultaneous threshold voltage $(V_{t})$ targeting for both n- and pFET in common gate and n/p-connection with vertical common contact were also verified in addition to our previous report [1]. As a result, we believe that the most of key components for ultimate cell height scaling of 3DSFET has been verified to continue the logic technology scaling beyond 1nm node.

The continuous increase of total number of word-line (WL) layers and the reduction of unit cell size make it difficult to implement quad-level cell (QLC) in 3D-NAND flash. In this paper, we introduce several technological breakthroughs to realize QLC with high performance and reliability for $7^{\mathrm{th}}$ generation 3D-NAND (7 th QLC). By introducing advanced technologies, the QLC reliability is enhanced by 74% compared to before the improvement, which is equivalent the previous generation QLC 3D-NAND with 92-layer (5 th QLC). Furthermore, the average performance is 25% increased and bit density is doubled compare to $5^{\mathrm{th}}$ QLC.

The industry leading 8th generation 1Tb 3D-NAND flash memory (8th 3D-NAND) has been developed while possessing the smallest unit cell volume among all 3D-NAND products. Despite increasing stacking layers from 176 to 236, we improved the uniformity of channel hole size by utilizing the state of the art HARC (high-aspect ratio contact) etching technology. Degradation of interference and retention characteristics due to the cell scale-down is overcome by several ingenious technologies, leading to the development of highly reliable high performance device.

A continuous Nondestructive monitoring method is required to apply proper feedback controls during tissue regeneration. Conductivity is one of valuable information to assess the physiological function and structural formation of regenerated tissues or cultured cells. However, conductivity imaging methods suffered from inherited ill-posed characteristics in image reconstruction, unknown boundary geometry, uncertainty in electrode position, and systematic artifacts. In order to overcome the limitation of microscopic electrical impedance tomography (micro-EIT), we applied a 3D-specific container with a fixed boundary geometry and electrode configuration to maximize the performance of Graz consensus reconstruction algorithm for EIT (GREIT). The separation of driving and sensing electrodes allows us to simplify the hardware complexity and obtain higher measurement accuracy from a large number of small sensing electrodes. We investigated the applicability of the GREIT to 3D micro-EIT images via numerical simulations and large-scale phantom experiments. We could reconstruct multiple objects regardless of the location. The resolution was 5 mm3with 30 dB SNR and the position error was less than 2.54 mm. This shows that the new micro-EIT system integrated with GREIT is robust with the intended resolution. With further refinement and scaling down to a microscale container, it may be a continuous nondestructive monitoring tool for tissue engineering applications.

Electrical Impedance Tomography (EIT) has potential for imaging of the head to image cerebral edema and stroke, and to assist the EEG inverse problem. One key challenge is the low distinguishability of head EIT. In this paper, we develop a strategy to improve distinguishability by optimizing electrode configurations and stimulation and measurement patterns. In a hemispherical simulation phantom, electrode positions and patterns were evaluated for (i) 1-ring 16 electrodes, (ii) 2-ring equal number of electrodes, (iii) 3-ring electrode geometries and (iv) 10-20 system of EEG electrode configuration. A selected best case was experimentally evaluated using a KHU Mark2 EIT system and compatible saline phantom. The objective was to design an EIT electrode geometry and stimulation pattern to yield high SNR across a large region of interest within the head. Results show that multi-level electrode geometries produced higher distinguishability, especially the multi-layer 10-20 electrode configuration provides the highest distinguishability and best image reconstruction performance.

Frequency-difference (FD) electrical impedance tomography (EIT) using a weighted voltage difference has recently been proposed for imaging haemorrhagic stroke, abdominal bleeding and tumors. Although its feasibility was demonstrated through two-dimensional numerical simulations and phantom experiments, we should validate the method in three-dimensional imaging objects. At the same time, we need to investigate its robustness against geometrical modeling errors in boundary shapes and electrode positions. We performed a validation study of the weighted FD method through three-dimensional numerical simulations and phantom experiments. Adopting hemispherical models and phantoms whose admittivity distributions change with frequency, we investigated the performance of the method to detect an anomaly. We found that the simple FD method fails to detect the anomaly, whereas reconstructed images using the weighted FD method clearly visualize the anomaly. The weighted FD method is robust against modeling errors of boundary-shape deformations and displaced electrode positions. We also found that the method is capable of detecting an anomaly surrounded by a shell-shaped obstacle simulating the skull. We propose the weighted FD method for future studies of animal and human experiments.

We present numerical simulations of frequency-difference electrical impedance tomography (EIT) for imaging haemorrhagic stroke inside the head adopting a multi-shell concentric spherical head model. We performed a validation study of a weighted frequency-difference method through three-dimensional numerical simulations. Adopting the multi-shell model with a frequency-dependent admittivity distribution, we investigated the performance of the method to detect a blood anomaly. We found that the simple frequency-difference method fails to detect the anomaly whereas reconstructed images using the weighted frequency-difference method clearly visualize the anomaly. We found that the weighted frequency-difference method is robust against modeling errors since it is capable of detecting an anomaly surrounded by shell-shaped obstacles simulating the internal structures of the head. We propose the weighted frequency-difference method for future studies of animal and human experiments.

This paper reviews recent progress and future outlook of PRAM as a promising candidate for emerging non-volatile memory. Electrical characteristics and reliability issues of PRAM with scale-down of the device dimension are discussed. Despite remarkable progress of PRAM properties in recent last decades, there are still several fundamental issues to resolve for broadening its application area. Several suggestions to overcome these property issues are introduced with recent experimental results.

We have proposed a new frequency difference method using a weighted voltage difference (WFD-EIT) between two frequencies [1, 2]. Previous studies demonstrated its feasibility through numerical experiments and two-dimensional phantom experiments. In this study, we validate the WFD-EIT algorithm on a three-dimensional hemisphere phantom using a multi-frequency EIT system KHU Mark1. We built the hemisphere phantom with 17 stainless-steel electrodes on its inner surface. We filled the phantom with a biological material having a frequency-dependent admittivity such as carrot pieces mixed in saline. Using boundary voltage data from the deformed phantom, we reconstructed weighted frequency difference images on the computational model domain with a hemisphere shape. We discuss comparative reconstruction performance results including time difference (TD), simple frequency difference (FD), and weighted frequency difference (WFD). Animal and human head imaging experiments with the weighted frequency-difference EIT method are under investigation.

Frequency-difference electrical impedance tomography (fdEIT) using a weighted voltage difference has been proposed as a means to provide images of admittivity changes at different frequencies. This weighted difference method is an effective way to extract anomaly information while eliminating background effects by unknown boundary geometry, uncertainty in electrode positions and other systematic measurement artefacts. It also properly handles the interplay between conductivity and permittivity in measured boundary voltage data. Though the proposed fdEIT algorithm is promising for applications such as detection of hemorrhagic stroke and breast cancer, more validation studies are needed. In this paper, we performed two-and three-dimensional numerical simulations and phantom experiments. Backgrounds of imaging objects were either saline or carrot pieces suspended in saline. We used carrot pieces to simulate a more realistic frequency-dependent admittivity distribution. Test objects were banana, potato or conductive gel with known admittivity spectra. When the background was saline, both simple and weighted difference approaches produced reasonably accurate images. The weighted difference method yielded better images from two-dimensional imaging objects with background of carrot pieces. For the three-dimensional head-shaped phantom, the advantage of the weighted frequency difference method over the simple difference method is not as obvious as in the case of the two-dimensional phantom. It is unclear if this is due to measurement errors or limitations in the linear algorithm. Further refinement and validation of the frequency difference image reconstructions are currently in progress.