Device Temperature Research Articles

Supercharged Fluorescent Protein-Apoferritin Cocrystals for Lighting Applications.

The application of fluorescent proteins (FPs) in optoelectronics is hindered by the need for effective protocols to stabilize them under device preparation and operational conditions. Factors such as high temperatures, irradiation, and organic solvent exposure contribute to the denaturation of FPs, resulting in a low device performance. Herein, we focus on addressing the photoinduced heat generation associated with FP motion and rapid heat transfer. This leads to device temperatures of approximately 65 °C, causing FP-denaturation and a subsequent loss of device functionality. We present a FP stabilization strategy involving the integration of electrostatically self-assembled FP-apoferritin cocrystals within a silicone-based color down-converting filter. Three key achievements characterize this approach: (i) an engineering strategy to design positively supercharged FPs (+22) without compromising photoluminescence and thermal stability compared to their native form, (ii) a carefully developed crystallization protocol resulting in highly emissive cocrystals that retain the essential photoluminescence features of the FPs, and (iii) a strong reduction of the device's working temperature to 40 °C, leading to a 40-fold increase in Bio-HLEDs stability compared to reference devices.

Numerical study of an infrared suppression (IRS) device with cooling hole configuration on the mixing tube

Hot walls of the infrared suppression (IRS) device intensify the infrared signature of warships, which is detrimental for attaining infrared stealth. In this work, to effectively reduce the wall temperature, hole cooling technology is innovatively adopted on a marine IRS device. Circular holes are arranged on the mixing tube of the device. Numerical simulations are conducted to predict the temperature and flow distribution. The current research comprehensively analyzes the effects of hole position, number of hole rows, and number of holes on the wall temperature of the mixing tube and heat shield. The air suction rate and the exit temperature of the whole device are considered as well. The results indicate that the air suction and exit temperature of the device do not significantly change with the hole arrangement parameters. As the hole position moves towards the mixing tube outlet, the average temperature of the mixing tube continuously increases, while the maximum temperature of the mixing tube exhibits a peak-and-valley pattern. When the holes with large diameters are located near the mixing tube inlet, a backflow occurs between the mixing tube and the heat shield, causing the heat shield temperature to rise appreciably. Increasing the number of hole rows can reduce the mixing tube temperature, but excessive hole rows lead to an elevation in the heat shield temperature. The optimal configuration for the number of hole rows is found to be 2 with a hole diameter of 80 mm. With the increment in hole number, the average temperature of the mixing tube rises due to the accelerated disappearance of the streamwise vortices behind the holes; however, the maximum temperature of the mixing tube shows a decreasing-then-increasing trend owing to that more streamwise vortices are created. This study paves the way for the practical application of hole cooling technology on marine IRS devices. The findings can provide instructive suggestions for the arrangement of cooling holes.

Epoxy composites based on phase change microcapsules with high thermal conductivity and storage efficiency by dispersing with cellulose nanofibrils

The incorporation of microencapsulated phase change materials (MPCMs) into electronic packaging materials has demonstrated the potential to reduce the transient increase in temperature of electronic devices under thermal loading. However, because of their high specific surface area, MPCMs tend to form severe aggregates in polymer matrices, resulting in poor thermal conductivity and energy storage efficiency. Therefore, in this paper, cellulose nanofibers (CNF) were used as dispersants to effectively disperse MPCMs in the epoxy resin matrix to synthesize epoxy composites with superior thermal conductivity and thermal storage properties (referred to as EBM-C). The results demonstrated that the addition of CNF improved the dispersion of MPCMs as well as the thermal conductivity and thermal storage capacity of the composites. The thermal conductivity and energy storage efficiency of the composites with 3 wt% CNF were increased by 100 %, and 97 %, respectively, compared to those of composites without CNF. In addition, the EBM-C composites also had excellent thermal stability and mechanical properties. The experimental results conclusively demonstrate that the EBM-C composites have tremendous application potential as thermal management materials.

Enhancement Effect of a Diamond Network on the Flow Boiling Heat Transfer Characteristics of a Diamond/Cu Heat Sink

The use of a micro heat sink is an effective means of solving the problem of high-power chip heat dissipation. Diamond/Cu composites exhibit high thermal conductivity and a linear thermal expansion coefficient that is compatible with semiconductor materials, rendering them ideal micro heat sink materials. The aim of this study was to fabricate diamond/Cu and Cu separately as heat sinks and subject them to flow boiling heat transfer experiments. The results indicate that the diamond/Cu heat sink displayed a decrease in wall superheat of 10.2–14.5 °C and an improvement in heat transfer coefficient of 38–51% compared with the Cu heat sink under identical heat fluxes. The heat sink also exhibits enhanced thermal uniformity. Secondary diamond particles are incorporated into the gaps of the main diamonds, thereby constructing a three-dimensional heat conduction network within the composite material. The diamond network enhances the internal heat flux of the material while also creating more nucleation sites on the surface. These increase the boiling intensity of the diamond/Cu heat sink, leading to better heat transfer performance. By combining the transient thermal model with computational fluid dynamics, a heat transfer model based on the diamond/Cu heat sink is proposed. The efficient heat dissipation capability of diamond/Cu heat sinks can lower the working temperature of microelectronic devices, thereby improving device performance and reliability during operation.

Investigating the thermal robustness of soliton crystal microcombs.

Soliton crystals are a novel form of microcomb, with relatively high conversion efficiency, good thermal robustness, and simple initiation among the methods to generate them. Soliton crystals can be easily generated in microring resonators with an appropriate mode-crossing. However, fabrication defects can significantly affect the mode-crossing placement and strength in devices. To enable soliton crystal states to be harnessed for a broader range of microcomb applications, we need a better understanding of the link between mode-crossing properties and the desired soliton crystal properties. Here, we investigate how to generate the same soliton crystal state in two different microrings, how changes in microring temperature change the mode-crossing properties, and how mode-crossing properties affect the generation of our desired soliton crystal state. We find that temperature affects the mode-crossing position in these rings but without major changes in the mode-crossing strength. We find that our wanted state can be generated over a device temperature range of 25 ∘C, with different mode-crossing properties, and is insensitive to the precise mode-crossing position between resonances.

Parametric analysis of a PCM-based heat sink for electronic device thermal management

Integrating conventional Heat Sinks with Phase Change Materials (HS-PCM) is a novel strategy for the thermal management of electronic devices. Although various studies attempted to investigate the impact of PCM on the operating temperature of electronic devices, the influence of PCM properties on the performance of the HS-PCM system remained unknown. Therefore, in the present study, an accurate three-dimensional HS-PCM system is designed and simulated to evaluate the effect of PCM properties, including thermal conductivity, enthalpy, specific heat capacity, and liquidus temperature, on the operating temperature of this system. In this order, the HS-PCM system is simulated at multiple operating conditions during both the working and cooling phases. Notably, an experimental setup is fabricated to compare the numerical outputs against the experimental data. Additionally, the Support Vector Regression with Hybrid (HSVR) kernels is used to predict the performance of the HS-PCM system. The hyperparameters of this machine learning model are optimized by implementing Grey Wolf Optimizer (GWO). It is found that raising the liquidus temperature of the PCM can have a minor impact on the working duration of the chipset while it dramatically impacts the cooling process of the system. Also, increasing the enthalpy and heat capacity of the PCM has a favorable effect on the working time of the chipset but extends the cooling process. Thermal conductivity is the only parameter which its enhancement has a positive impact on both the working and cooling duration of the chipset. Raising the thermal conductivity of the PCM from 0.05 W/(m·K) to 0.8 W/(m·K) improves the working duration of the chipset from 22 min to 24 min. Based on the outcomes, the most effective factor on the working time of the chipset is the enthalpy, followed by heat capacity, thermal conductivity, and the liquidus point of the PCM. According to the findings, the GWO-HSVR model can accurately forecast the outcomes of the HS-PCM system at the both working and cooling phases. In the testing process of the model, the values of R2 for the working and cooling phases are calculated to be 0.99174 and 0.99775, respectively.

Deconvolution of heat sources for application in thermoelectric micro four-point probe measurements

Joule heating is a primary phenomenon responsible for increasing temperature in electronic devices, and consequently, decreasing the lifetime and performance of electronic devices. However, this unwanted Joule heating can itself be used as a local source of heat to map the temperature-dependent material properties. Recently, micro four-point probe (M4PP) showed a promising potential for characterizing the temperature coefficient of resistance (TCR) and the Seebeck coefficient using Joule heating resulting from the measurement current. Here, we use M4PP to estimate the micrometer scale, relative temperature profile resulting from a single heat source. We introduce a triplet of four-point voltages measured at the second harmonic frequency, to deconvolute the thermoelectric voltage from the three individual heat sources involved. This paper tests and documents the validity of the proposed scheme in the 1–40 μm range on highly doped single crystal Si at 300 K, supporting predominantly Fourier heat transport at these scales. The method of deconvolution of heat sources reduces the complexity in evaluation of length- and time-dependent measurements, specifically used in the characterization of thermoelectric properties. The proposed method may also facilitate a more profound understanding of heat transport on the mesoscopic scale.

Investigation and Evaluation of High-Temperature Encapsulation Materials for Power Module Applications

With the advent of ultra-wide bandgap (UWBG) semiconductor materials, such as Gallium Oxide (Ga2O3) and Aluminum Nitride (AlN), higher temperature and higher voltage operation of power devices is becoming realizable. However, conventional polymeric and organic encapsulant materials are typically limited to operating temperatures of 200 °C and below. In this work, six materials were identified and evaluated as candidates for use as encapsulants for operation and high-voltage insulation at and above 250 °C. High-temperature silicone gel was used as a reference material and was compared to five novel encapsulants including an epoxy resin, a hydro-set cement, two low melting point glass compounds, and a ceramic potting compound. Gas pycnometry was utilized to evaluate the voiding concentration to avoid partial discharge. Each material was then processed onto a direct-bonded-aluminum (DBA) substrate test coupon to evaluate compatibility with a commonly used metal-ceramic substrate and processability for use in a power module. The insulation capability of each material was evaluated by testing the partial discharge inception voltage (PDIV) across a 1mm gap etched in the substrate. The dielectric stability was then tested by soaking the materials in air at 250 °C for various intervals and observing the degradation of their PDIVs and appearances. The results of each test were compared, and conclusions were drawn about each material’s feasibility for use as a dielectric encapsulation material for a power module operating at temperatures exceeding 200 °C.

Investigation on the control strategy of new spray cooling system based on PV/T and heat recovery in sow houses: As a case study in Nanchang, China

The uncertain cooling effect and additional huge primary energy consumption caused by humidity regulation are currently the main problems of traditional air-conditioning systems in sow houses. In order to address the above problems, a new spray cooling system is proposed based on PV/T and heat recovery in sow houses in this paper. Compared with traditional spray cooling systems, the cooling efficiency of new system can be improved and its energy consumption can be reduced due to solar dehumidification and heat recovery. Meanwhile, the mathematical models are established for its key equipment and their reliability is verified according to literature data. The results show that the maximum error is less than 7.2% for the models. The main operating parameters affecting the system characteristics are determined through simulation. The results show that with the changes in the set inlet temperature of second heat exchanger (IHET), the set subcooled temperature (SCT) and the set superheated temperature (SHT) of sensible heat exchanger, the total energy consumption and gain of new system are changed by 2%–11.9%, while they are changed by 54.5%–86% with the changes in the set inlet relative humidity of rotary dehumidifier (IRH) and the set inlet temperature of spray device (ISDT). In other words, the total energy consumption and gain of new system are slightly affected by IHET, SCT and SHT, but significantly affected by IRH and ISDT. The annual control strategy is further proposed for the new system. In cooling season, supply air of sow house will be dehumidified, heat exchanged with exhaust air and cooled, and the optimal setting ranges of operating parameters are IRH = 70%, SCT = 18 °C, SHT = 26 °C and ISDT = 22–24 °C. In heating season, it will be heat exchanged with exhaust air and heated, and the optimal setting ranges of operating parameters are SCT = 19 or 20 °C, SHT = 26–28 °C and IHET = 22–24 °C. The above research will provide guidance for the improvement of traditional spray cooling systems and the operating control of new system.

Site‐Selective Enhancement of Superconducting Nanowire Single‐Photon Detectors via Local Helium Ion Irradiation

AbstractAchieving homogeneous performance metrics between nominally identical pixels is challenging for the operation of arrays of superconducting nanowire single‐photon detectors (SNSPDs). Here, local helium ion irradiation is utilized to post‐process and tune single‐photon detection efficiency, switching current, and critical temperature of individual devices on the same chip. For 12 nm thick highly absorptive SNSPDs, which are barely sensitive to single photons with a wavelength of 780 nm prior to He ion irradiation, an increase of the system detection efficiency from <0.05% to (55.3 1.1)% is observed following irradiation. Moreover, the internal detection efficiency saturates at a temperature of 4.5 K after irradiation with 1800 ions nm−2. Compared to 8 nm SNSPDs of similar detection efficiency, a doubling of the switching current (to 20 µA) is observed for irradiated 10 nm thick detectors, increasing the amplitude of detection voltage pulses. Investigations of the scaling of superconducting thin film properties with irradiation up to a fluence of 2600 ions nm−2 revealed an increase of sheet resistance and a decrease of critical temperature towards high fluences. A physical model accounting for defect generation and sputtering during helium ion irradiation is presented and shows good qualitative agreement with experiments.

Junction temperature prediction method of GaN HEMT power devices based on accurate on-voltage testing

Compared with Si devices, GaN HEMT has lower on-resistance, lower junction capacitance, higher switching frequency, higher switching speed and higher junction temperature capability. It is widely used in automotive, aerospace and other fields. Severe environments may cause the junction temperature of GaN-HEMT to be too high, and excessive temperature is the main reason for power device failure. In order to ensure stable operation of GaN devices under harsh conditions, it is important to extract junction temperature information of semiconductor devices simply and effectively. However, most of the existing junction temperature prediction methods are not applicable to GaN HEMT devices due to its high switching speed and high requirement of prediction accuracy. Thus, we proposed a new method based on an accurate on-voltage clamp circuit to predict the junction temperature of GaN HEMT devices. The interrelation between the on-resistance and the junction temperature is analyzed, and the temperature coefficient is calibrated to obtain the corresponding relationship between the characterization quantity and the junction temperature. The on-resistance testing circuit suitable for GaN device is given and analyzed in detail. Finally, the conduction resistance testing circuit is used to predict the junction temperature of GaN devices, achieving extremely high accuracy. Experiments have verified under 100 ℃, the predicted junction temperature and the actual junction temperature have achieved more than 90% coincidence.

Diode paremeters extraction and study of space charge limited current in (Ag, Au)/CoS2 Schottky diodes

We investigated the electron transport properties of cobalt sulphide Schottky diodes with Au and Ag metal contacts. Pure CoS2 nanoplates were synthesized using solid state reaction method. From temperature dependent IV characterstics diode parameters including ideality factor, barrier height and Richardson cofficient were calculated for Au/CoS2 and Ag/CoS2 diodes. The value of barrier height increased with increasing temperature for both devices, however Ideality factor showed different trend. The values of modified Richardson coefficient by assuming the Gaussian distribution of the barrier heights turns out to be 244.20Acm−2K−2 and 348.20Acm−2K−2 for Au/CoS2 and Ag/CoS2 diodes respectively. At high voltages we observed Space Charge Limited Current (SCLC) with an exponential trap distribution in Au/CoS2 diode. The density of the traps and characteristic temperature associated with these traps were determine to be 2.47×1014cm−3 and 141 K, respectively.

Stagnation Point Flow of CoF e 2 O 4 / Ti O 2 - H 2 O -Casson Nanofluid past a Slippery Stretching/Shrinking Cylindrical Surface in

Mounting temperatures in electronic devices during operation may damage sensitive internal components if too much thermal energy accumulates inside the system. The advent of an innovative ultrahigh-performance thermal management technology known as nanofluid has provided a veritable platform to improve the system performance and reliability by removing the high heat flux generated in the engineering and industrial devices. This paper examines the combined effects of Darcy–Forchheimer porous medium-resistant heating and viscous dissipation on stagnation point flow of a Casson nanofluid ( CoF e 2 O 4 - H 2 O and Ti O 2 - H 2 O ) towards a convectively heated slippery stretching/shrinking cylindrical surface in a porous medium. The governing nonlinear model equations are obtained, analysed, and tackled numerically via the shooting technique with the Runge–Kutta–Fehlberg integration scheme. A unique solution is obtained when the surface is stretching. For shrinking cylindrical surface, the model exhibits nonunique dual solutions for a defined range of parameter values, and a temporal stability analysis is conducted to ascertain the stable and physically achievable solution. The effects of emerging thermophysical parameters on the overall flow structure and thermal management such as velocity and temperature profiles, skin friction, and Nusselt number are quantitatively discussed through graphs and in tabular form. It is found that the thermal performance heat transfer enhancement capability of Ti O 2 - H 2 O is higher than that of CoF e 2 O 4 - H 2 O . Moreover, the nanofluid thermal performance is enhanced with nanoparticles volume fraction, Casson nanofluid parameter, and Biot number but lessened with porous medium permeability.

Correlation between Electronic Structure, Microstructure, and Switching Mode in Valence Change Mechanism Al2O3/TiOx‐Based Memristive Devices

AbstractMemristive devices with valence change mechanism (VCM) show promise for neuromorphic data processing, although emulation of synaptic behavior with analog weight updates remains a challenge. Standard filamentary and area‐dependent resistive switching exhibit characteristic differences in the transition from the high to low resistance state, which is either abrupt with inherently high variability or gradual and allows quasi‐analog operation. In this study, the two switching modes are clearly correlated to differences in the microstructure and electronic structure for Pt/Al2O3/TiOx/Cr/Pt devices made from amorphous layers of 1.2 nm Al2O3 and 7 nm TiOx by atomic layer deposition. For the filamentary mode, operando spectromicroscopy experiments identify a localized region of ≈50 nm in diameter of reduced titania surrounded by crystalline rutile‐like TiO2, highlighting the importance of Joule heating for this mode. In contrast, both oxide layers remain in their amorphous state for the interfacial mode, which proves that device temperature during switching stays below 670 K, which is the TiO2 crystallization temperature. The analysis of the electronic conduction behavior confirms that the interfacial switching occurs by modulating the effective tunnel barrier width due to accumulation and depletion of oxygen vacancies at the Al2O3/TiOx interface. The results are transferable to other bilayer stacks.

Nanocavity enhanced photon coherence of solid-state quantum emitters operating up to 30 K

Solid-state emitters such as epitaxial quantum dots have emerged as a leading platform for efficient, on-demand sources of indistinguishable photons, a key resource for many optical quantum technologies. To maximise performance, these sources normally operate at liquid helium temperatures ( ∼4 K ), introducing significant size, weight and power requirements that can be impractical for proposed applications. Here we experimentally resolve the two distinct temperature-dependent phonon interactions that degrade indistinguishability, allowing us to demonstrate that coupling to a photonic nanocavity can greatly improve photon coherence at elevated temperatures up to 30 K that are compatible with compact cryocoolers. We derive a polaron model that fully captures the temperature-dependent influence of phonons observed in our experiments, providing predictive power to further increase the indistinguishability and operating temperature of future devices through optimised cavity parameters.

Flexible highly thermally conductive biphasic composite films for multifunctional solar/electro-thermal conversion energy storage and thermal management

Phase change materials (PCMs) have been widely used for thermal energy storage in overcoming the intermittence of renewable energy and passive thermal management. However, low thermal conductivity, leakage, inherent brittleness, and lack of responses under multiple stimuli preclude their widespread applications. Here, we report a flexible and form-stable solid-solid/solid-liquid biphasic phase change composites to achieve efficient solar/electro-thermal energy conversion and storage as well as thermal management of high-power devices simultaneously. Proposed biphasic polyurethane–stearic acid/expanded graphite (PU–SA/EG) composites demonstrate state-of-the-art performances with a high energy storage density of 117.4–137.3 J/g and high thermal conductivity of 10.98–37.80 W/(m⋅K) simultaneously at an EG loading ratio of 10–30 wt %, benefiting from the formation of continuous thermal transport network provided by expanded graphite nanosheets. PU–SA/EG maintains high flexibility and good thermal reliability over more than 500 melting/solidification cycles. High solar- and electro-thermal conversion and storage efficiencies of up to 90.5% and 88.7% are achieved, respectively. When applied in thermal management of flexible electronic devices, PU–SA/EG film demonstrates a superior cooling performance by reducing device temperature prominently by 32 °C under a DC 5A discharging power supply. This work provides an effective way for harvesting and storing multiple energy sources like solar energy and electricity, as well as thermal management of high-power electronic devices.

Experimental and numerical investigation of a compact vapor compression refrigeration system for cooling of avionics in harsh environments

The power density and heat dissipation requirements of electric/electronics devices have significantly increased due to miniaturization. This is especially critical with the emergence of the “more electric aircraft concept” (MEA), which demands higher heat dissipation. The future thermal management systems must possess high heat removal capability and effectively handle heat loads of individual components in line with MEA objectives. Moreover, they should perform optimally in the highly dynamic and harsh aviation environments, e.g. elavated temperatures. Compact vapor compression refrigeration (VCR) systems have garnered interest as they excel in eliminating high heat flux and keeping device temperatures lower to ensure better performance in challenging environments. This paper presents the design, development, and testing of a compact VCR system applicable at the device level. The studied compact refrigeration system, with dimensions of 600 mm × 400 mm × 250 mm and weighing 2.8 kg, utilizes R134a as its working fluid and incorporates a miniature refrigeration compressor. It achieves heat dissipation of up to 623 W at an ambient temperature of 50°C, attaining a COP of 2.7 while maintaining device temperatures lower than or close to ambient levels. Through simulations and experiments, the system's dynamic performance is assessed under varying heat loads and ambient temperatures. Experimental validation of the model has been carried out at various conditions. Overall, the proposed compact vapor compression system proves to be an excellent solution for thermal management in harsh conditions, aligning well with the requirements of the modern electric aircraft concepts.

Auger-suppression in barrier-blocking HgCdTe long-wavelength infrared detector

Throughout, both the Auger-suppression effect and barrier-blocking devices have been regarded as highly promising solutions for achieving high- operation-temperature (HOT) in long-wave infrared (LWIR) HgCdTe devices. Herein, two structural designs of pBin-type barrier-blocking LWIR HgCdTe devices were introduced and analyzed, accompanied by an extensive investigation into the Auger-suppression effect within the designed structures. It was observed that this unique structural approach has the potential to enhance the operational temperature of HgCdTe barrier-blocking devices. A strong dependency of the Auger suppression effect on the doping concentration within the absorption region was revealed through the analysis of absorption region structural parameters. Furthermore, the analysis of band structures for different design configurations demonstrated that the structural design involving p-type barrier layers can effectively position the barrier at the conduction band, eliminating the reliance on valence band-offset with respect to barrier layer structural parameters. Consequently, the structural design and fabrication processes of the devices were significantly simplified. These discoveries offer theoretical guidance for the simplification of structural design and fabrication processes in HOT barrier-blocking HgCdTe devices, emphasizing the potential of pBin-type structures in enhancing device performance and achieving elevated operational temperatures.

Measurement, calibration, and verification on the critical ignition temperature of hot bridge wire electro-explosive device

To address the problem of the difference in temperature between the exposed and amorce-filled state of the bridge wire in the fiber optic thermometry, this paper proceeds from a mathematical model of the temperature rise of the hot bridge wire electro-explosive device (EED), the relationship between the critical ignition temperature and the current of hot bridge wire EED is discussed. Combining thermal ignition theory, the technique of measurement and calibration the critical ignition temperature of hot bridge wire EED is proposed, and the technique is validated by injection versus radiation. The results show that the critical ignition temperature of the tested hot bridge wire EED obtained by testing and calibration is 337.53 °C. The 50% ignition field strength of the hot bridge wire EED under radiation conditions obtained by the up-and-down method test is 1271 V m−1, while the equivalent ignition field strength determined from the critical ignition temperature under the same radiation conditions is 1345 V m−1, the error between the two is only 0.49 dB, which demonstrates the high accuracy of the proposed measurement and calibration technique.

Shape memory polymer with programmable recovery onset.

Stimulus-responsive shape-shifting polymers1-3 have shown unique promise in emerging applications, including soft robotics4-7, medical devices8, aerospace structures9 and flexible electronics10. Their externally triggered shape-shifting behaviour offers on-demand controllability essential for many device applications. Ironically, accessing external triggers (for example, heating or light) under realistic scenarios has become the greatest bottleneck in demanding applications such as implantable medical devices8. Certain shape-shifting polymers rely on naturally present stimuli (for example,human body temperature for implantable devices)8 as triggers. Although they forgo the need for external stimulation, the ability to control recovery onset is also lost. Naturally triggered, yet actively controllable, shape-shifting behaviour is highly desirable but these two attributes are conflicting. Here we achieved this goal with a four-dimensional printable shape memory hydrogel that operates via phase separation, with its shape-shifting kinetics dominated by internal mass diffusion rather than by heat transport used for common shape memory polymers8-11. This hydrogel can undergo shape transformation at natural ambient temperature, critically with a recovery onset delay. This delay is programmable by altering the degree of phase separation during device programming, which offers a unique mechanism for shape-shifting control. Our naturally triggered shape memory polymer with a tunable recovery onset markedly lowers the barrier for device implementation.