Post-trim Drift Research Articles

Polysilicon resistor trimming by laser link making

A technique for laser trimming of polysilicon resistors has been developed. In this scheme an undoped polysilicon film is patterned lithographically, and then photoresist patterns are used to prevent doping of certain narrow areas of each resistor during the impurity implant; thus, the protected areas remain insulating after wafer processing. Subsequent laser scanning of the undoped regions can produce precise reductions in resistance by lateral diffusion of dopant impurities. Trimming can be accomplished by changing either the laser power or the position. Q-switched Nd:YAG (1.06- mu m wavelength) and second-harmonic (0.53- mu m wavelength) radiations have produced successful results. The process was applied to passivated resistors with negligible (perhaps zero) post-trim drift, and the temperature coefficients of resistivity (TCRs) of trimmed resistors can be matched to the TCRs of untrimmed resistors in the same film.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Trimming studies on polymer thick-film resistors

PVC-graphite polymer thick-film resistors were trimmed by a conventional air abrasive technique and the post-trim drift in resistance with time was found to be negative. The net decrease in resistance of trimmed resistors in a given time was found to be a function of resistor composition, cutting speed and temperature. Detailed studies showed this decrease to be due to a decrease in cut width with time. Two new methods, namely bombardment trimming and radiation trimming, were also tried for adjusting the resistance of these resistors and the results were compared with those obtained from abrasive trimming studies.

Strain Sensivity of Thick-Film Resistors

The strain sensitivity measurements of Dupont 1400Biroxr thick-film resistor materials in untrimmed and laser trimmed conditions are described. This was studied to better understand the post-laser trim drift phenomenon and evaluate the effect of packaging/assembly induced stresses on the resistors. The strain coefficient of resistance or the strain sensitivity of the untrimmed 102_ 106 \Omega / \Box$^b$ resistor materials is small, reversible, and independent of resistor geometry or fired thickness (t f ). This strain sensitivity (?i) is an intrinsic material property which is determined by the conduction mechanism in the material. The strain sensitivity of the laser trimmed · resistors is a sum of the intrinsic sensitivity (?i) and an additional term called the extrinsic strain sensitivity (\gamma ex ). The additional extrinsic contribution can be large and irreversible and depends strongly on the fired thickness (t f of the resistor. A mechanism is proposed to explain these observations. The mismatch of the thermal expansion coefficients of the resistor material and the substrate leads to high internal stresses in the thick resistor. Hence crack formation and propagation is easier which leads to increased strain sensitivity (extrinsic) and post-trim drift. It was experimentally determined that Al 2 O 3 from the substrate dissolved 6-8 µm into the thick-film resistor during resistor firing. For thin resistors the relatively higher amount of dissolved Al 2 O 3 from the substrate in the resistor glass reduces the thermal expansion mismatch between the fired resistor and substrate. Thus its strain sensitivity and drift are much smaller than a thicker fired resistor.

Trimming Behavior and Post-Trim Characteristics of Ta&amp;lt;inf&amp;gt;2&amp;lt;/inf&amp;gt;N Resistors on Silicon

Laser trimming of thin films on silicon differs in several important respects from trimming on passive substrates such as ceramic. These differences necessitate the characterization of the process and its effect on circuit performance. The trimming behavior of Ta 2 N thin-film resistors on silicon is studied in detail. Incremental changes in resistance are investigated for several important geometrical configurations. These results are of special value in trimming under measure and predict conditions. It is also shown that the laser trimming of these resistors results in post-trim drift. However, it is shown that proper design guidelines can minimize the effect so that high-precision monolithic circuits can be successfully produced.

Reducing post-trim drift of thin-film resistors by optimizing YAG laser output characteristics: Robert Dow, Michael Mauck, Thomas Richardson and Edward Swenson IEEE Trans. Components. Hybrids, Mfg Technol. Chmt.-1, (4) 392 (December 1978)

Reducing post-trim drift of thin-film resistors by optimizing YAG laser output characteristics: Robert Dow, Michael Mauck, Thomas Richardson and Edward Swenson IEEE Trans. Components. Hybrids, Mfg Technol. Chmt.-1, (4) 392 (December 1978)

Reducing post-trim drift of thin-film resistors by optimizing YAG laser output characteristics : Robert Dow. Michael Mauck, Thomas Richardson and Edward Swenson. IEEE Trans. Components. Hybrids, Mfg Technol. Chmt.-1, (4) 392 (December 1978)

Reducing post-trim drift of thin-film resistors by optimizing YAG laser output characteristics : Robert Dow. Michael Mauck, Thomas Richardson and Edward Swenson. IEEE Trans. Components. Hybrids, Mfg Technol. Chmt.-1, (4) 392 (December 1978)

Reducing Post-Trim Drift of Thin-Film Resistors by Optimizing YAG Laser Output Characteristics

A study to determine the effects of laser parameters on tantalum nitride resistor stability is presented. A model Of the laser heat affected zone is proposed which relates laser pulse width, power, wavelength, repetition rate, and waist size parameters to energy delivered to remaining resistor material. Samples of qualified tantalum nitride resistors are trimmed with a range of laser parameters, and the results are compared with the model. The excellent agreement between the model and experiment allows these results to be used for process control and throughput versus tolerance calculations.

Mechanism and Control of Post-Trim Drift of Laser-Trimmed Thick-Film Resistors

Some of the important parameters controlling the postlaser trim drift of 100, l-K, 10-K, and 100-K <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">\Omega//\Box$^b$</tex> thick-film resistors are reported. The fired thickness of the resistor plays a major role in the control of post-trim drift. The resistors with fired thickness (tf) <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">\leq</tex> 0.5 mil show small ( <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">\DeltaR/R \leq</tex> 0.3 percent) and predictable drift, whereas those with t <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">f</inf> > 0.5 mil produce large ( <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">\DeltaR/R \geq</tex> 0.3 percent) and unpredictable drift. A mechanism for the post-trim drift is proposed. Results indicate that the percent trimming for precision resistors should be held within 25 to 30 percent range for minimum drift. The trim geometry such as L-cuts or two P-cuts from the same side of the resistor produces the least amount of drift. The protective overglaze coating on the resistors has a beneficial effect of reducing the drift, especially for the resistors with t <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">f</inf> > 0.5 mil. The resistor size (L X W) does not significantly influence the drift as long as the t <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">f</inf> < 0.5 mil.

Reducing post trim drift of thin film resistors by optimizing YAG laser output characteristics : Robert Dow, Michael Mauck, Thomas Richardson and Edward Swenson. Proc. IEEE 28th Electron. Components Conf., Anaheim, 24–26 April 1978, p. 87

Reducing post trim drift of thin film resistors by optimizing YAG laser output characteristics : Robert Dow, Michael Mauck, Thomas Richardson and Edward Swenson. Proc. IEEE 28th Electron. Components Conf., Anaheim, 24–26 April 1978, p. 87

Mechanism and control of post-trim drift of laser-trimmed thick-film resistors : Jayant S. Shah and Lloyd Berrin. IEEE Trans. Components, Hybrids, Mfg Technol.CHMT-1, (2) 130 (June 1978)

Important characteristics of boron-doped LPCVD polysilicon layers with regard to sensor applications are presented. Properties such as the resistivity, temperature coefficient of the resistance, gauge factor and long-term stability are described. A pressure sensor utilizing polysilicon piezoresistors with a measurement range of 1 bar and a sensitivity of roughly 11 mV/V FS, a laser-trimmed polysilicon temperature sensor with a sensitivity of −3.4 × 10−3 K−1 and non-linearity of less than 0.5% and a pressure sensor with polysilicon-based on-chip calibration and temperature compensation are described.

Mechanism and control of post-trim drift of laser trimmed thick film resistors : J. S. Shah and L. Berrin. Proc. Electron. Components Conf. Arlington, Va., May 16–18, 1977. p. 254

Anomalous current-voltage (I-V) characteristics, as reported with increasing frequency, can significantly compromise the energy conversion efficiency of colloidal quantum dot (CQD) solar cells. This paper applied a purely hopping transport model rather than the traditional Schottky-diode equation to interpret the anomalous I-V curves measured in CQD solar cells with a structure: ITO/ZnO/PbS-TBAI QD/PbS-EDT QD/Au. Anomalous I-V curves were found at temperatures below 300 K. A double-diode-equivalent electric circuit was developed for the quantitative analysis of these anomalous I-V curves, yielding multiple hopping transport parameters, such as hopping diffusivity, diffusion length, mobility, and lifetime. Quantitative analysis revealed that the imbalanced charge carrier mobility in the carrier transport (PbS-TBAI) and extraction (PbS-EDT) layers, as well as the existence of a reverse Schottky diode at the PbS-EDT/Au interface, played key roles in the formation of the anomalous I-V curves. Furthermore, charge-transfer (CT) states, located at the ZnO/PbS-TBAI interface, were found to reduce the CQD solar cell open-circuit voltage through radiative and non-radiative recombination of excitons. A modified Einstein equation was also validated, further proving the presence of a Schottky barrier and pointing to a rate determining interface for the I-V behaviors of our solar cells.