Total Ionizing Dose Response Research Articles

Evaluation of Enhanced Low Dose Rate Sensitivity in Fourth-Generation SiGe HBTs

The total ionizing dose response of 4th-generation SiGe HBTs is assessed at both low and high dose rates to evaluate enhanced low dose rate sensitivity (ELDRS) in a new SiGe BiCMOS technology. Both device and circuit results are presented. A bandgap reference circuit topology is chosen to monitor for ELDRS in TID-induced collector current shifts, which have previously been reported in low dose rate studies of SiGe HBTs. The results in this paper also cover previous technology generations from this foundry in order to incorporate a broader view of dose rate effects in SiGe HBTs. No indication of ELDRS was found in any technology generation.

Sample-to-Sample Variability and Bit Errors Induced by Total Dose in Advanced NAND Flash Memories

The variability in the total ionizing dose response of 25-nm single level cell NAND Flash memories from two different lots is studied. More than 1 Terabit of floating gate cells were irradiated with gamma rays and the number of errors was statistically analyzed. The behavior of the two lots is remarkably different in terms of floating gate errors. The statistical parameters such as mean, standard deviation, and shapes of the error distributions were studied. The sample-to-sample statistical distribution of TID errors is not Gaussian and it is attributed to variability in neutral cells, due to phenomena such as random discrete dopant fluctuations. Finally, the impact of scaling on variability is discussed.

Advanced SiGe BiCMOS Technology for Multi-Mrad Electronic Systems

The total ionizing dose response of both CMOS transistors and SiGe HBTs implemented without utilizing any radiation hardening by design techniques in Jazz Semiconductor's SBC-18-HXL BiCMOS technology platform is evaluated. The SiGe HBTs remain functional up to the 6 Mrad (SiO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> ) dose levels needed to support multi-Mrad exploration missions such as NASA's Europa mission. The CMOS devices are also functional to this extreme total dose. The nFETs exhibit significantly reduced shallow trench isolation leakage compared with nFETs implemented in prior SiGe BiCMOS processes. Both nFETs and pFETs show negligible transconductance and on-current degradation. We conclude that this SiGe process technology is a potential candidate for implementing reliable and survivable multi-Mrad total ionizing dose-hard electronic systems.

Total ionizing dose response of fluorine implanted Silicon-On-Insulator buried oxide

A comparison is made of the behavior of silicon on insulator buried oxides and wet thermal oxides before and after fluorine implantation and irradiation. Before irradiation, the electrical characteristics of the thermal oxide and buried oxide are significantly different. The fluorine implantation in the smart-cut® buried oxide results in a large negative threshold shift due to the trapping of positive charges. These charges are associated with positively charged fluorine ions on implantation and are trapped at pre-existing trap sites, particularly at the bonding interface, and at additional defects caused by the ion implantation damage. This shift is absent in the wet thermal oxide. After Co60 irradiation up to 500Krad(Si), the negative flatband and threshold voltage shift in the fluorine implanted buried oxide is larger than in the unimplanted buried oxide indicating that any potential positive effect of fluorine on the passivation of interface states is more than offset by the additional trapping sites created during implantation. These results demonstrate that in the design of a transistor utmost care must be taken to prevent any fluorine being implanted into the buried oxide.

Investigation of the total dose response of partially depleted SOI nMOSFETs using TCAD simulation and experiment

We have analyzed total ionizing dose response of partially depleted SOI nMOSFETs fabricated in a 0.13μm commercial technology assisted by TCAD simulation. Using TCAD tools, the ionizing radiation-induced damages in buried oxide and shallow-trench oxide are investigated separately. It is shown that back transistors are radiation tolerant up to 1Mrad (Si) for core nMOSFETs even under the worst case whereas back transistors of I/O devices are 100krad (Si) due to lower doping concentration. In addition, the enhanced total dose degradation with applied gate bias is attributed to more charge trapped in shallow-trench oxide. 2D cross section electrical simulation schematically illustrates the evolution of charge trapping in buried oxide and shallow-trench oxide. It is found and verified that parasitic corner transistor located at the bottom of swallow-trench oxide plays a critical role on the radiation hardness of partially depleted SOI nMOSFETs.

TID Radiation Response of 3-D Vertical GAA SONOS Memory Cells

The total ionizing dose response against the γ ray of 3-D silicon-oxide-nitride-oxide-nitride (SONOS) cells with a vertical polysilicon channel was investigated. No leakage current increase or subthreshold slope degradation is observed up to the total ionizing dose of 1 Mrad(Si) even for devices scaled down to 22 nm, as the gate-all-around structure provides better control over the potential in the body, and shallow trench isolation oxide is not required. The threshold voltage (VT) shifts trend during radiation is similar to the behavior of 2-D cells, and can be well predicted with McWhorter's model. Benefiting from a larger initial memory window before irradiation, 3-D SONOS cells have a significant memory window of 4.5 V after exposure to a high radiation dose of 1 Mrad(Si). These results clearly indicate that 3-D SONOS devices are promising as radiation-tolerant memories.

Using Charge Accumulation to Improve the Radiation Tolerance of Multi-Gb NAND Flash Memories

Consecutive write operations on 42-nm and 60-nm single-level cell (SLC) Samsung NAND flash memories are shown to significantly improve both the total ionizing dose response and the single event upset tolerance of the memory. By writing these SLC flash memories multiple times, more charge is placed on the floating gate. This accumulated charge leads to a larger amount of radiation needed to corrupt the data. The work presented in this paper illustrates a path forward to the development of a multi-gigabit rad-hard non-volatile memory.

Impact of X-Ray Exposure on a Triple-Level-Cell NAND Flash

The total ionizing dose response of a triple-level-cell (TLC) NAND flash is shown to be low enough that data corruption can occur as a result of an x-ray inspection. Only a few seconds of x-ray exposure corresponding to a total dose of merely 50 rad(Si) in a real-time x-ray source are required to induce errors. An in-depth total dose analysis shows which pages of the memory and data patterns are the most susceptible to radiation. The results show that TLC NAND flash devices are not suitable for use in high radiation environments, and that care must be taken when exposing them to even small x-ray exposures like those present in a circuit board inspection.

Intrinsic Tolerance to Total Ionizing Dose Radiation in Gate-All-Around MOSFETs

We measured the total ionizing dose response of gate-all-around silicon nanowire n- and pMOSFETs to x-ray doses up to 2Mrad(SiO2). We show that they are radiation hard, with no degradation in threshold voltage, off-state current, or subthreshold slope, even at the highest dose for a wide range of bias conditions. We attribute this to the intrinsically rad-hard feature of the gate-all-around device design, where the channel is no longer in contact with any insulating layers that could form a parasitic channel.

Bias Dependence of Total-Dose Effects in Bulk FinFETs

The total ionizing dose response of triple-well FinFETs is investigated for various bias conditions. Experimental results show that irradiation with the transistor in the OFF state with the drain terminal high is the worst-case bias configuration. TCAD simulations are used to analyze the buildup of trapped charge in the trench isolation oxide and its impact on the increase in leakage current and subthreshold-slope degradation. The electric field distribution along the STI/fin boundary exerts a strong influence on the trapped charge in the isolation oxide, which induces a parasitic leakage current path at total ionizing doses of less than 200 krad(SiO2).

Total-Ionizing-Dose Radiation Effects in AlGaN/GaN HEMTs and MOS-HEMTs

<?Pub Dtl=""?> We have investigated the total ionizing dose (TID) radiation effects in AlGaN/GaN MOS-HEMTs as a function of dose and radiation bias, and compared them with conventional HEMTs. Under 10 keV X-ray irradiation, two distinct regimes of threshold voltage <formula formulatype="inline" xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex Notation="TeX">$(V_{th})$</tex> </formula> shifts have been revealed: a rapid <formula formulatype="inline" xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex Notation="TeX">$V_{th}$</tex></formula> shift at low doses <formula formulatype="inline" xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex Notation="TeX">$[&lt; {3}{\rm krad (SiO}_{2})]$</tex></formula> for both HEMTs and MOS-HEMTs, and an additional <formula formulatype="inline" xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex Notation="TeX">$V_{th}$</tex></formula> shift only found in MOS-HEMTs for doses up to at least 2 Mrad <formula formulatype="inline" xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex Notation="TeX">$({\rm SiO}_{2})$</tex></formula> . The rapid <formula formulatype="inline" xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex Notation="TeX">$V_{th}$</tex> </formula> shift anneals quickly and is a strong function of layer material. We attribute this portion of the <formula formulatype="inline" xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex Notation="TeX">$V_{th}$</tex> </formula> shift to hole trapping in the AlGaN barrier layer. The <formula formulatype="inline" xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex Notation="TeX">$V_{th}$</tex></formula> shift at high doses found only in MOS-HEMTs is attributed to hole trapping in the gate oxide. By comparing MOSFETs with <formula formulatype="inline" xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex Notation="TeX">${\rm HfO}_{2}$</tex></formula> and <formula formulatype="inline" xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex Notation="TeX">${\rm Al}_{2} {\rm O}_{3}$</tex></formula> gate dielectrics that are annealed during processing at various temperatures, we find that <formula formulatype="inline" xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex Notation="TeX">$500^{\circ}{\rm C}$</tex></formula> annealed <formula formulatype="inline" xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex Notation="TeX">${\rm HfO}_{2}$</tex></formula> shows the most promising TID response.

The total ionizing dose effects of non-planar triple-gate transistors

This paper investigates the total ionizing dose response of different non-planar triple-gate transistor structures with different fin widths. By exposing the pseudo-MOS transistor to different amounts of radiation, different interface trap densities and trapped-oxide charges can be obtained. Using these parameters together with Altal 3D simulation software, the total dose radiation response of various non-planar triple-gate devices can be simulated. The behaviors of three kinds of non-planar devices are compared.

Total Ionizing Dose Response of Triple-Well FET-Based Wideband, High-Isolation RF Switches in a 130 nm SiGe BiCMOS Technology

The effects of 63 MeV proton irradiation on the RF performance (insertion loss, isolation, and linearity) of triple-well nFET-based RF switches designed in a 130 nm SiGe BiCMOS technology are investigated. The switches were designed for wide-band operation (1 to 40 GHz) and were required by the application to achieve high isolation (> 35 dB at 40 GHz) with moderate insertion loss (dB at 40 GHz). The RF switch IL improves (S21 increases) at 100 and 500 krad(SiO2), but degrades (S21 decreases) at 2 Mrad(SiO2). P1dB and IIP3 (switch linearity) shows a similar TID response, at 100 and 500 krad(SiO2) dose an increase of ~ 0.4 dBm and ~0.2 dBm, respectively. However, at 2 Mrad(SiO2) both sharply decrease. Standalone RF and dc structures were also irradiated to better understand the underlying mechanisms affecting the switch RF performance. The bias dependence of the radiation-induced change on the measured RF performance of a SPST switch is also analyzed. 10 keV X-ray radiation experiments were conducted on separate dc transistor structures to provide additional insight into the measured impact of total ionization dose on the performance of RF switches.

From Displacement Damage to ELDRS: Fifty Years of Bipolar Transistor Radiation Effects at the NSREC

The fifty year history of radiation effects in bipolar transistors at NSREC is summarized, covering neutron-induced displacement damage, total ionizing dose response (including enhanced low dose rate sensitivity, ELDRS) and single event effects. These phenomena, particularly TID and ELDRS in bipolar transistors, have received significant attention at NSREC. Several other radiation effects such as thermal mechanical shock, electrical overstress, prompt dose rate photoresponse and the response to neutral particle beams are not addressed.

Radiation Effects in Advanced Multiple Gate and Silicon-on-Insulator Transistors

The aim of this review paper is to describe in a comprehensive manner the current understanding of the radiation response of state-of-the-art Silicon-on-Insulator (SOI) and FinFET CMOS technologies. Total Ionizing Dose (TID) response, heavy-ion microdose effects and single-event effects (SEEs) will be discussed. It is shown that a very high TID tolerance can be achieved by narrow-fin SOI FinFET architectures, while bulk FinFETs may exhibit similar TID response to the planar devices. Due to the vertical nature of FinFETs, a specific heavy-ion response can be obtained, whereby the angle of incidence becomes highly important with respect to the vertical sidewall gates. With respect to SEE, the buried oxide in the SOI FinFETs suppresses the diffusion tails from the charge collection in the substrate compared to the planar bulk FinFET devices. Channel lengths and fin widths are now comparable to, or smaller than the dimensions of the region affected by the single ionizing ions or lasers used in testing. This gives rise to a high degree of sensitivity to individual device parameters and source-drain shunting during ion-beam or laser-beam SEE testing. Simulations are used to illuminate the mechanisms observed in radiation testing and the progress and needs for the numerical modeling/simulation of the radiation response of advanced SOI and FinFET transistors are highlighted.

Effect of Accumulated Charge on the Total Ionizing Dose Response of a NAND Flash Memory

Consecutive write operations performed on a Samsung NAND flash memory are shown to significantly increase the total ionizing dose level at which data corruption occurs. Consequences of multiple consecutive write operations are discussed as well as the mechanisms at work. Elevated temperature exposure and page location within a block of the memory are shown to have significant effects on the amount of data corruption observed. The hardness assurance implications of these effects are discussed.

Impact of Back-Gate Bias and Device Geometry on the Total Ionizing Dose Response of 1-Transistor Floating Body RAMs

In this paper we investigate how geometry impacts the memory characteristics of 1-transistor dynamic floating body RAMs (FBRAMs) under total ionizing dose exposure. FBRAMs are implemented using fully depleted silicon-on-insulator devices with ultrathin buried oxide and body. Analytical models and experimental data are used to quantify the effects of charge trapping in the oxides and spacers on the memory read window shifts. The effects of increased radiation-induced leakage and interface trapping on the retention time are also discussed. Small geometry devices show reduced memory window shifts compared to large devices, but the retention time degradation is higher. The effects of coupling between interfaces and back-gate bias are also discussed in the context of memory characteristics.

Fin Width and Bias Dependence of the Response of Triple-Gate MOSFETs to Total Dose Irradiation

The total ionizing dose response of triple-gate MOSFETs is investigated for various fin widths and bias conditions. Experiments and simulations are used to analyze the buildup of trapped charge in the buried oxide and its impact on the threshold-voltage shift and subthreshold-slope degradation. The higher total-dose tolerance of multiple-gate FinFETs with narrow fins is attributed to lateral gate control over the electrostatic potential in the body and especially at the Si fin/BOX interface. It is demonstrated that ON-state irradiation is the worst-case bias configuration for triple-gate MOSFETs through extensive experimental analysis.

Including Radiation Effects and Dependencies on Process-Related Variability in Advanced Foundry SPICE Models Using a New Physical Model and Parameter Extraction Approach

An automated flow is described for total-ionizing dose (TID)-aware SPICE model generation that includes TID response and its dependence on process variability and layout. A memetic algorithm that balances multiple objectives, subject to realistic constraints, is introduced for global optimization of the flow. A differential evolution algorithm is adapted for global exploration, and a modified random pattern search strategy is introduced for local exploitation. The optimizer efficiently reduces the value of different kinds of objective functions in the extraction at reasonable cost and avoids premature convergence in most practical cases. The model is implemented in Verilog-A, can be applied to all foundry model formats, and supports all popular SPICE simulators. To validate the flow, simulations from models extracted from specific targets are compared with measured current-voltage characteristics under various irradiation conditions for 0.35 μm, 0.18 μm, and 90 nm bulk CMOS processes.

Analysis of bias effects on the total ionizing dose response in a 180 nm technology

The effects of gamma ray irradiation on the shallow trench isolation (STI) leakage current in a 180nm technology are investigated. The radiation response is strongly influenced by the bias modes, gate bias during irradiation, substrate bias during irradiation and operating substrate bias after irradiation. We found that the worst case occurs under the ON bias condition for the ON, OFF and PASS bias mode. A positive gate bias during irradiation significantly enhances the STI leakage current, indicating the electric field influence on the charge buildup process during radiation. Also, a negative substrate bias during irradiation enhances the STI leakage current. However a negative operating substrate bias effectively suppresses the STI leakage current, and can be used to eliminate the leakage current produced by the charge trapped in the deep STI oxide. Appropriate substrate bias should be introduced to alleviate the total ionizing dose (TID) response, and lead to acceptable threshold voltage shift and subthreshold hump effect. Depending on the simulation results, we believe that the electric field distribution in the STI oxide is the key parameter influencing bias effects on the radiation response of transistor.