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Silicon channel ferroelectric field-effect transistors (FeFETs) with low-k interfacial layer (IL) between ferroelectric and silicon channel suffers from high write voltage, limited write endurance and long read-after-write latency. This is due to early IL breakdown and mobile charge injection at the ferroelectric-IL interface. Here, we demonstrate low voltage, high speed memory operation with high write endurance using an IL-free back-end-of-line (BEOL) compatible FeFET. We fabricated IL-free FeFETs with 28nm channel length (Lg) and 126nm width under a thermal budget < 4000 C by integrating 5nm Hf0.5Zr0.5O2 (HZO) gate stack with amorphous Indium Tungsten Oxide (IWO) semiconductor channel. We report a voltage memory window of 1.6V with a read current window ${I}_{\textit {LVT}}{/}{I}_{\textit {HVT}}$ of 105, write voltage of ±1.6V with 20ns pulses, instantaneous read-after-write latency < 300ns and a record high write endurance exceeding 1011 cycles. This establishes the IL-free BEOL FeFET as a promising candidate for logic-compatible high-performance last-level cache memory. [ABSTRACT FROM AUTHOR]

Monolithic 3D (M3D) integration has been emerged as a promising technology for fine-grained 3D stacking. As the M3D integration offers extremely small dimension of via in a nanometer-scale, it is beneficial for small microarchitectural blocks such as caches, register files, translation look-aside buffers (TLBs), etc. However, since the M3D integration requires low-temperature process for stacked layers, it causes lower performance for stacked transistors compared to the conventional 2D process. In contrast, non-volatile memory (NVM) such as magnetic RAM (MRAM) is originally fabricated at a low temperature, which enables the M3D integration without performance degradation. In this paper, we propose an energy-efficient unified L2 TLB-cache architecture exploiting M3D-based SRAM/MRAM hybrid memory. Since the M3D-based SRAM/MRAM hybrid memory consumes much smaller energy than the conventional 2D SRAM-only memory and 2D SRAM/MRAM hybrid memory, while providing comparable performance, our proposed architecture improves energy efficiency significantly. Especially, as our proposed architecture changes the memory partitioning of the unified L2 TLB-cache depending on the L2 cache miss rate, it maximizes the energy efficiency for parallel workloads suffering extremely high L2 cache miss rate. According to our analysis using PARSEC benchmark applications, our proposed architecture reduces the energy consumption of L2 TLB + L2 cache by up to 97.7% (53.6% on average), compared to the baseline with the 2D SRAM-only memory, with negligible impact on performance. Furthermore, our proposed technique reduces the memory access energy consumption by up to 32.8% (10.9% on average), by reducing memory accesses due to TLB misses.

Monolithic 3-dimensional integration (M3D) requires heat treatment techniques that should not degrade the device performance of the lower layers when applied to device fabrication in the upper layers. Deep ultraviolet (DUV) laser annealing was implemented in the crystallization of amorphous silicon and source/drain junction activation to fabricate polycrystalline silicon (poly-Si) metal-oxide-semiconductor field-effect-transistors (MOSFETs) for upper-layer devices. The poly-Si MOSFET devices were fabricated successfully on top of the bottom electronic circuit layer (isolated by a thick silicon dioxide layer). Devices on the upper and lower layers were connected through interlayer vias to form a current-starved ring oscillator. The current-to-frequency converter on the bottom layer showed a reasonable increase in frequency as the current of the poly-Si MOSFET on the upper layer increased with increasing silicon grain size, confirming that DUV laser annealing did not degrade the performance of the bottom layer devices. This opens more opportunities for using DUV laser annealing in the M3D integration. [ABSTRACT FROM AUTHOR]

Self-heating has emerged as an important performance/reliability challenge for modern MOSFETs. The challenge is further acerbated for III-V transistors, especially when integrated monolithically in a 3-D platform for applications in ultrafast logic, imagers, etc. A key challenge is the difficulty of heat-dissipation through the ultra-thin channels needed to ensure electrostatic integrity of scaled transistors. In this paper, we demonstrate an innovative use of a heat-dissipating shunt of Ni-InGaAs on InGaAs(111) in the S/D extension region, as well as the use of high-conductivity Mo contact to simultaneously improve electrical and thermal stability and heat dissipation in III-V transistors, such that the peak channel temperature is reduced by as much as 25%-30%. Given the exponential temperature sensitivity of transistor reliability, heat shunts will improve transistor lifetime significantly.

Monolithic 3-D integration has emerged as a promising technological solution for traditional transistor scaling limitations and interconnection bottleneck. The challenge we must overcome is a processing temperature limit for top side devices in order to ensure proper performance of bottom side devices. To solve this problem, we developed a low temperature III-V and Ge layer stacking process using wafer bonding and epitaxial lift-off, since these materials can be processed at a low temperature and provide extended opportunity/functionality (sensor, display, analog, RF, etc.) via heterogeneous integration. In this paper, we discuss technology for integrating III-V and Ge materials and its applicability to CMOS, thin film photodiodes, mid-infrared photonics platforms, and MicroLED display integration for creating the ultimate 3-D chip of the future.

This paper evaluates monolithic 3-D logic circuits and 6T SRAMs composed of InGaAs-n/Ge-p ultra-thin-body MOSFETs while considering interlayer coupling through TCAD mixedmode model. This paper indicates that monolithic 3-D InGaAs/Ge logic circuits provide equal leakage and better delay performance compared with planar 2-D structure through optimized 3-D layout. The monolithic 3-D InGaAs/Ge 6T SRAMs can simultaneously improve the cell stability and performance through optimized 3-D layout. We suggest two 3-D SRAM layout designs for high performance and low power applications, respectively. Moreover, with optimized 3-D layout designs, InGaAs/Ge logic circuits exhibit larger delay improvement, and the 6T SRAMs exhibit larger read access time and time-to-write improvement compared with Si counterparts.

Like the parallel computers of the 1980s and 1990s, today’s 3D-chip technology will require new theory in software and algorithms to fully exploit. [ABSTRACT FROM AUTHOR]

Rather than continue the expensive and time-consuming quest for transistor replacement, the authors argue that 3D chips coupled with new computer architectures can keep Moore’s law on its traditional scaling path. [ABSTRACT FROM PUBLISHER]

Three-dimensional sequentially stackable high- k /metal-gate-stacked tri-gate nanowire poly-Si FETs with embedded source/drain (e-S/D) and back gate were demonstrated. The highly crystallized channel, fabricated by green nanosecond laser crystallization, chemical mechanical polish, and postsurface modification processes, enhances the electrical property of the tri-gate nanowire FET. The e-S/D structure reduces the contact and series resistances caused by the nanowire structure. Thus, the fabricated n/p-type tri-gate nanowire poly-Si FETs exhibit steep subthreshold swings (96/125 mV/decade), high ON-currents (232/110 \mu \text{A}/\mu \text{m} ), and I_{{\mathrm{\scriptscriptstyle {on}}}}/I_{\mathrm{\scriptscriptstyle {OFF}}} ratio ( > 10^5) . Furthermore, the independent back gate with thin back gate oxide can easily adjust the threshold voltage of the tri-gate nanowire transistor and results in high gamma value (>0.05) FET realizing sequentially stacked and low V\mathrm {dd} (0.6 V) operable inverter. [ABSTRACT FROM PUBLISHER]

To enable monolithic three-dimensional integration of the amorphous In–Ga–Zn–O (a-IGZO) and CMOS technologies, the a-IGZO inverters compatible with the low operating voltage ( $\leqq 1$ V) and process temperature of back-end-of-line CMOS have been investigated. We demonstrated a full-swing depletion-load inverter with a voltage gain up to 24 using a CMOS-compatible operating voltage of 1 V. The drive transistor was realized using a low-voltage enhancement-mode a-IGZO thin-film transistor (TFT) with a steep subthreshold swing of 70 mV/decade and a low threshold voltage of 0.5 V. The load transistor was implemented using a bi-layer a-IGZO channel, where the a-IGZO composition was modulated simply by the oxygen flow rate in a depletion-mode TFT. [ABSTRACT FROM AUTHOR]

Monolithic 3D (M3D) is an emerging technology that enables integration density which is orders of magnitude higher than that offered by through-silicon-vias. In this paper, we demonstrate that a modified 2D placement technique coupled with a post-placement partitioning step is sufficient to produce high-quality M3D placement solutions. We also present a commercial router-based monolithic intertier via insertion methodology that improves the routability of M3D ICs. We demonstrate that, unlike in 2D ICs, the routing supply and demand in M3D ICs are not completely independent of each other. We develop a routing demand model for M3D ICs, and use it to develop an O(N) min-overflow partitioner that enhances routability by off-loading demand from one tier to another. This technique reduces the routed wirelength and the power delay product by up to 7.44% and 4.31%, respectively. This allows a two-tier M3D IC to achieve, on average, 19.9% and 11.8% improvement in routed wirelength and power delay product over 2D, even with reduced metal layer usage. [ABSTRACT FROM PUBLISHER]