April 1, 2003

Version 1.5

# Characterization of L1 sensor prototypes (WBS 1.1.1.3.2.3)

L1 sensors prototypes were ordered from two vendors -- HPK and ELMA. By
October 2002 both vendors have deliver pilot sensors -- 10 from HPK, 9
from ELMA. 4 additional ELMA sensors were received in November. QA
measurements were done at Fermilab and at KSU probing site according to
the QA document. Mechanical measurements are done at Fermilab on OGP.

Three HPK sensors and two ELMA sensors were irradiated in 10 MeV protons
beam to equivalent dose of up to 2.75x10^14^ 1 MeV n/cm^2^ at J.R.
MacDonald's irradiation facility at KSU.

### Electric Test Grading

All sensors were tested electrically according to the procedures
outlined in the QA document. Electric testing of the sensors before
irradiation was done at room temperature. Each sensor was given a grade
based on its compliance with the specifications.

-   ET1 grade: Depletion voltage is determined using CV measurement. If
    Vdepl is below 300V the sensor receives 2 points, otherwise it
    receives 0 points.

> ![](media/image1.wmf){width="5.9944444444444445in"
> height="3.3958333333333335in"}
>
> 1/C^2^ vs V dependence for HPK #4. Depletion voltage is determined to
> be 117V.
>
> ![](media/image2.wmf){width="5.9944444444444445in"
> height="3.3958333333333335in"}
>
> 1/C^2^ vs V dependence for ELMA #1. Depletion voltage is determined to
> be 26V.

-   ET2 grade: Breakdown voltage is determined using IV measurement. If
    Vbreak is above 700V the sensor receives 2 points, otherwise it
    receives 0 points. If Vbreak\<500V overall electric grade for such
    sensor is set to zero: ET=0.

> ![](media/image3.wmf){width="5.997222222222222in"
> height="3.232638888888889in"}
>
> IV dependence of ELMA 01 sensors shows a breakdown at \~350V.

-   ET3 grade: Leakage current at depletion voltage +50V is determined
    using IV measurement. If Ileak is below 100 nA/cm^2^ (1722nA total)
    the sensor receives 2 points, otherwise it receives 0 points.

-   ET4 grade: Number of bad channels is determined using a combination
    of AC, DC and Rpoly measurements as outlined in the specifications.
    If the number of bad strips is 3 or below the sensor receives 2
    points, if it is from 4 to 7 the sensor receives 1 point, sensors
    with more than 7 bad strips receive 0 points.

***Definition of not working channels:***

-   Pinholes -- current through capacitor \>10 nA at 80 V and RT

-   Short -- coupling capacitor \>1.2 times the typical value

-   Open - coupling capacitor \<0.8 times the typical value

-   Leaky channel if leakage current above 10 nA/strip at FDV and RT

-   Rpoly must be between 0.8±0.3 MΩ,  otherwise the channel is
    considered bad.

```{=html}
<!-- -->
```
-   ET5 grade: averaged interstrip capacitance on up to 5 strips per
    sensor is determined at Vdepl+50V. If the interstrip capacitance
    C_int is less or equal than 1.2 pF/cm the sensor receives 2 points,
    if C_int is 1.2\<C_int\<1.4 pF/cm it will receive 1 point, otherwise
    0 points.

-   ET grade: After these tests are completed the electric test grade
    for each sensor is calculated:

> ET=(ET1+ET2+ET3+ET4+ET5)/5

-   ET=0, if two or more individual grades are 0.

```{=html}
<!-- -->
```
-   Vendor grade for electric test is calculated as an average ET over
    10 sensors. If electric GPA is equal or below 1.0 the vendor is
    disqualified.

> The following table summarizes the results of electrical grading for
> HPK sensors.
>
> ![](media/image4.wmf)
>
> Overall electrical grade for HPK prototype sensors is the maximum
> possible 2.0.
>
> In the following table we present the electrical grading of the ELMA
> sensors.
>
> ![](media/image5.wmf)
>
> Overall electrical grade for ELMA prototype sensors is 1.36. ELMA
> sensors suffer from low breakdown voltage (all but one sensors have a
> break down voltage in the region of about 300V) and high number of bad
> channels -- mostly shorts and opens.

### Irradiation Test Grading

Randomly selected sensors from the ten electrically tested ones (HPK 20,
11, 12 and Elma 07, 12) were irradiated to equivalent dose of up to
2.75x10^14^ 1 MeV n/cm^2^. Electric testing of these sensors after
irradiation was done at 1^o^C temperature. Sensor performance after
irradiation is graded as well and irradiation test GPA is calculated.

-   IT1 grade: Depletion voltage is determined using CV measurement. If
    Vdepl is below 700V after 1.6x10^14^ 1 MeV n/cm^2^ the sensor
    receives 2 points, otherwise it receives 0 points.

> After each irradiation session the detectors are allowed to anneal at
> 60^o^C for 80 min. The following plot shows the depletion voltage
> behavior of the irradiated HPK sensors.
>
> ![](media/image6.wmf){width="4.746527777777778in" height="2.69375in"}
>
> 1/C^2^ vs V dependence of HPK \# 12 sensor after 1.1E14 n/cm2. The
> depletion voltage is determined to be 85V.
>
> ![](media/image7.wmf){width="5.99375in" height="4.107638888888889in"}
>
> The experimentally determined behavior is compared to the prediction
> of Hamburg model with the following parameters:

  ----------------------------------- -------------------- --------------
  Model parameters                                         units

  Nc,0/Neff,0                         0.8                  

  c                                   6.50E-14             cm-1

  gc                                  1.49E-02             cm-1

  ga                                  1.67E-02             cm-1

  d                                   3.20E-02             cm

  tau_a                               1.90E+01             min

  Ny,inf/flux                         5.29E-02             cm-1

  tau_y                               1.26E+03             min
  ----------------------------------- -------------------- --------------

> For all three irradiated sensors the depletion voltage is below 250V
> and thus for HPK IT1=2.
>
> The following plot shows the depletion voltage behavior of the
> irradiated ELMA sensors.
>
> ![](media/image8.wmf){width="5.99375in" height="4.107638888888889in"}
>
> For both irradiated sensors the depletion voltage is below 400V and
> thus for ELMA IT1=2.

-   IT2 grade: Breakdown voltage is determined using IV measurement. If
    Vbreak is above 700V the sensor receives 2 points. If
    Vdepl+100V\<Vbreak\<700V after irradiation IT2=1, otherwise the
    sensor receives 0 points.

> The following set of plots show the evolution with irradiation of the
> IV dependence for HPK sensors. After irradiation the leakage current
> was measured at 1^o^C.
>
> ![](media/image9.wmf){width="5.99375in" height="4.107638888888889in"}
>
> ![](media/image10.wmf){width="5.9944444444444445in"
> height="3.111111111111111in"}
>
> ![](media/image11.wmf){width="5.9944444444444445in"
> height="3.111111111111111in"}
>
> Two out of three HPK sensors develop a breakdown at voltages that are
> below 700V, but above depletion voltage plus 100V and for this reason
> they are graded IT2=1, thus the overall grade for HPK
> IT2=(1+1+2)/3=1.33
>
> The following set of plots show the evolution with irradiation of the
> IV dependence for ELMA sensors.
>
> ![](media/image12.wmf){width="5.9944444444444445in"
> height="3.111111111111111in"}
>
> N.B. IV dependence of ELMA 07 sensor after 275E12 n/cm^2^ (blue curve)
> was measured at 5^o^C because of the problem with condensation due to
> high humidity, while all the other measurements were done at 1^o^C.
>
> ![](media/image13.wmf){width="5.9944444444444445in"
> height="3.111111111111111in"}
>
> Results on ELMA L1 #07 shows signs of soft breakdown and receives
> IT2=1. Sensor #12 receives IT2=2.

-   IT3 grade: Leakage current at depletion voltage +50V is determined
    using IV measurement. The sensor has to be fully annealed. If Ileak
    at T=0 ^o^C is below 55 uA/cm^2^ (950 uA total) the sensor receives
    2 points, between 55 uA/cm^2^ (950 uA total) and 70 uA/cm^2^ (1200
    uA total) it receives 1 point, otherwise it receives 0 points.

> The following plot shows the total leakage current scaled to 20^o^C
> for HPK sensors. Green dotted line corresponds to α=3E-17 A/cm.
>
> ![](media/image14.wmf){width="5.99375in" height="4.107638888888889in"}
>
> All HPK sensors receive IT3=2.
>
> The following plot shows the total leakage current for ELMA sensors
> scaled to 20^o^C. Green dotted line corresponds to α=3E-17 A/cm.
>
> ![](media/image15.wmf){width="5.99375in" height="4.107638888888889in"}
>
> All ELMA sensors receive IT3=2.
>
> The following plot shows the temperature dependence of the total
> leakage current compared to the theoretically predicted one.
>
> ![](media/image16.wmf){width="5.99375in" height="4.107638888888889in"}

-   IT4 grade: Number of additional pinholes is determined using AC
    strip measurements and added to the number of bad channels measured
    before irradiation. If the number of bad strips is 7 or below the
    sensor receives 2 points, if it is from 8 to 11 the sensor receives
    1 point, sensors with more than 11 bad strips receive 0 points.

> No additional pinholes were found in HPK and ELMA sensors. Very small
> number of new shorts and opens was observed, but considering that
> these sensors were subject to multiple handling scratches and dust are
> inevitable. All sensors receive IT4=2.0.

-   IT5 grade: averaged interstrip capacitance C_int on up to 5 strips
    per sensor is determined at Vdepl+50V. If the interstrip capacitance
    is less or equal than 1.4 pF/cm (=10.9 pF for L1 sensors) the sensor
    receives 2 points, if C_int is 1.4\<C_int\<1.6 pF/cm
    (10.9\<Cint\<12.4pF) it will receive 1 point, otherwise 0 points.

> The Cint measurement was done at 500V bias voltage for both ELMA and
> HPK sensors using one-neighbor scheme:
>
> ![](media/image17.wmf){width="4.997916666666667in"
> height="2.872916666666667in"}
>
> The Cint is determined to be 5pF for ELMA sensor and 4 pF for HPK
> sensor, thus both manufactures receive IT5=2.

-   IT grade: After these tests are completed the electric test grade
    for each sensor is calculated:

> IT=(IT1+IT2+IT3+IT4+IT5)/5
>
> IT=0, if two or more individual grades are 0.

-   Vendor grade for electric test is calculated as an average IT over 3
    sensors. If irradiation GPA is equal or below 1.0 the vendor is
    disqualified.

> The following table summarizes the irradiation grading of HPK sensors.
>
> ![](media/image18.wmf)
>
> The following table summarizes the irradiation grading of ELMA
> sensors.
>
> ![](media/image19.wmf)

###  Mechanical Test Grading

5 non-irradiated sensors from each vendor are measured on the OGP
metrology machine at Fermilab.

-   MT1 grade: The overall sensor warp is measured. If the warp is
    smaller than ±25 μm the sensor receives 2 points, if the warp is
    between ±25 and ±50 μm, then the sensor will receive 1 points,
    otherwise 0 points.

-   MT2 grade: The cutting line is checked. If the cutting line is in
    between ±10 μm with respect to the nominal line, then the sensor
    receives 2 points. If it is in between ±20 μm, the sensor receives 1
    point and otherwise 0 points.

-   The final MT grade is calculated by the averaged sum MT=(MT1+MT2)/2.

-   There is no immediate disqualification due to the mechanical
    grading.

> ![](media/image20.wmf) ![](media/image21.wmf)

### Overall GPA 

Overall GPA is calculated as a weighted average of the electric,
mechanical and irradiation GPAs according to the following rule:
0.4\*ET + 0.4\*IT + 0.2\*MT.

Vendor with the highest overall GPA wins.

In a situation if the difference in the overall GPA is less than 10%,
the production volume of the respective vendor will play the decisive
role in order to minimize the production risk.

Marginal failure to comply with mechanical tolerances does not
immediately result in vendor dismissal but these results have to be
discussed further within the Run 2b Silicon group and with the
respective vendor.

**GPA without Cint after irrad**:

**HPK overall GPA = 0.4\*2.00 + 0.4\*1.87 + 0.2\*1.50 = 1.85**

**ELMA Overall GPA = 0.4\*1.36 + 0.4\*1.90 + 0.2\*0.36 = 1.38**

**Based on this study HPK is chosen as a vendor for L1 sensors.**

## L0 vendor choice

Same vendor is chosen for L0 sensor production.

###  {#section .unnumbered}