A hermetic sealing method of sub-mm sized microelectronic chiplets for wireless body implants is presented by ultrathin and electromagnetically transparent Atomic Layer Deposition (ALD) coatings. Fully 3-dimensional (3D) conformal encapsulation of wirelessly powered microdevices is demonstrated both with and without opening windows for electrophysiological measurements. The chiplets embedding custom CMOS application specific integrated circuits (ASICs) with RF transmitters are encapsulated by a stack of alternating layers of Hafnium oxide (HfO 2 ) and Silicon dioxide (SiO 2 ) as the strategy to maximize impermeability of water and ionic penetration while minimizing the volume of the packaging material. The hermeticity of the devices is characterized through accelerated aging tests in saline at T=87˚C while continued functionality is monitored via evaluation of backscattered RF signals (near 1 GHz) to ascertain possible degradation and electronic failure. Earliest failures of wirelessly functional devices have occurred after more than 180 days of immersion at 87˚C. Wireless device having opening windows through ALD envelope have not shown any signs of degradation for more than 95 days so far. This implies an equivalent lifetime >10 years at T=37˚C. This approach is readily scalable to high throughput batch processing of hundreds of microchiplets, offering a methodology for hermetic packaging of microscale biomedical chronic implants.

Development of an in situ technique for measuring electrochemical impedance spectra in real time during an electrochemical experiment is described. The technique is based on staircase voltammetry with relatively large step heights, in which a series of increasing potential steps are applied to an electrochemical system, and the resulting currents are sampled. The first derivatives of the currents thus obtained are then converted to ac current signals in frequency domain, and impedances are computed from them. To demonstrate the technique as a tool for studying the electrode/electrolyte interface during the electrochemical reaction, we chose an electrochemical oxidation reaction of aniline, whose reaction products have been known to continuously change the electrode surface due to the polymer film growth on its surface, and report a number of observations that would not have been obtained without such in situ experiments. A suggestion is also made on the use of staircase voltammetry for mechanistic studies on complex electrochemical reactions by simply varying the sampling time.

We studied the effect of Gd doping on the structural properties of solution processed, crystalline In2O3 for thin-film transistor (TFT) application. With increasing Gd in In2O3 up to 20%, the material structure changes into amorphous phase, and the oxygen vacancy concentration decreases from 15.4 to 8.4%, and M-OH bonds from 33.5 to 23.7%. The field-effect mobility for the Gd doped In2O3 TFTs decreases and threshold voltage shifts to the positive voltage with increasing Gd concentration. In addition, the stability of the solution processed TFTs can also be improved by increasing Gd concentration. As a result, the optimum Gd concentration is found to be ∼5% in In2O3 and the 5% Gd doped In2O3 TFTs with the Y2O3 passivation layer exhibit the linear mobility of 9.74 cm2/V s, the threshold voltage of −0.27 V, the subthreshold swing of 79 mV/dec., and excellent bias stability.

Previous work has shown that certain steroidal bis-(N-phenyl)ureas, derived from cholic acid, form crystals in the P61 space group with unusually wide unidimensional pores. A key feature of the nanoporous steroidal urea (NPSU) structure is that groups at either end of the steroid are directed into the channels and may in principle be altered without disturbing the crystal packing. Herein we report an expanded study of this system, which increases the structural variety of NPSUs and also examines their inclusion properties. Nineteen new NPSU crystal structures are described, to add to the six which were previously reported. The materials show wide variations in channel size, shape, and chemical nature. Minimum pore diameters vary from ∼0 up to 13.1 Å, while some of the interior surfaces are markedly corrugated. Several variants possess functional groups positioned in the channels with potential to interact with guest molecules. Inclusion studies were performed using a relatively accessible tris-(N-phenyl)urea. Solvent removal was possible without crystal degradation, and gas adsorption could be demonstrated. Organic molecules ranging from simple aromatics (e.g., aniline and chlorobenzene) to the much larger squalene (Mw = 411) could be adsorbed from the liquid state, while several dyes were taken up from solutions in ether. Some dyes gave dichroic complexes, implying alignment of the chromophores in the NPSU channels. Notably, these complexes were formed by direct adsorption rather than cocrystallization, emphasizing the unusually robust nature of these organic molecular hosts.