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page_id: wsd-what-mimcaps-can-we-use-on-gf180mcu-b630d962
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title: "Thread: What mimcaps can we use on gf180mcu?"
slug: wsd-what-mimcaps-can-we-use-on-gf180mcu-b630d962
route: /evidence/i-information/questions/threads/what-mimcaps-can-we-use-on-gf180mcu
section: reference
access: public
summary: 20 Discord messages from ℹ️ - Information/⁉️-questions/threads/what-mimcaps-can-we-use-on-gf180mcu.md.
status: published
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tags: [discord, wafer-space, archive]
last_updated: 2026-08-19
talk_url: /evidence/i-information/questions/threads/what-mimcaps-can-we-use-on-gf180mcu.talk.md
talk_route: /evidence/i-information/questions/threads/what-mimcaps-can-we-use-on-gf180mcu/talk
---
# Thread: What mimcaps can we use on gf180mcu?
Category: **ℹ️ - Information**
Parent channel: **#⁉️-questions**
Thread ID: `1511221611238522991`
Messages: **20**
## message-1511221611238522991
**2026-06-02T04:15:09.259+00:00 — were491 (@were491.)**
- Message ID: `1511221611238522991`
- Author ID: `325334453213986816`
- Nickname: were491
- User name: were491.
- Type: `Default`
- Discord message: https://discord.com/channels/1361349522684510449/1511221611238522991/1511221611238522991
- Archive source: https://discord.wafer.space/wafer-space/%E2%84%B9%EF%B8%8F%20-%20Information/%E2%81%89%EF%B8%8F-questions/what-mimcaps-can-we-use-on-gf180mcu/2026-06/2026-06.json
- Archive source: https://discord.wafer.space/wafer-space/Information/questions/what-mimcaps-can-we-use-on-gf180mcu/2026-06/2026-06.json
**Content**
```text
*Insert obligatory "Sorry if this was really obvious..." here.*
When placing mimcaps in layout, we have the option for mimcap option MIM-A or MIM-B, and also the option to choose which layers we place between.
[This post](https://discord.com/channels/1361349522684510449/1444137681712971898/1444236820249317426) seems to suggest that we should use MIM-B between M4-M5 (on top of M4).
* Is MIM-B with M4-M5 the only MIM configuration we're allowed to use? What others can we use, if any?
The docs page [referenced](https://gf180mcu-pdk.readthedocs.io/en/latest/analog/layout/inter_specs/inter_specs_3_43.html) in the above message suggests there are two possibilities for the SiN thickness, which lead to different capacitances.
* What is the SiN thickness used in waferspace gf180mcu?
Thanks.
```
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---
## message-1511240045099483146
**2026-06-02T05:28:24.234+00:00 — tnt (@246tnt)**
- Message ID: `1511240045099483146`
- Author ID: `596068704471482370`
- Nickname: tnt
- User name: 246tnt
- Type: `Default`
- Discord message: https://discord.com/channels/1361349522684510449/1511221611238522991/1511240045099483146
- Archive source: https://discord.wafer.space/wafer-space/%E2%84%B9%EF%B8%8F%20-%20Information/%E2%81%89%EF%B8%8F-questions/what-mimcaps-can-we-use-on-gf180mcu/2026-06/2026-06.json
- Archive source: https://discord.wafer.space/wafer-space/Information/questions/what-mimcaps-can-we-use-on-gf180mcu/2026-06/2026-06.json
**Content**
```text
Yes, MIM-B is what you can use.
```
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---
## message-1511240096819580938
**2026-06-02T05:28:36.565+00:00 — tnt (@246tnt)**
- Message ID: `1511240096819580938`
- Author ID: `596068704471482370`
- Nickname: tnt
- User name: 246tnt
- Type: `Default`
- Discord message: https://discord.com/channels/1361349522684510449/1511221611238522991/1511240096819580938
- Archive source: https://discord.wafer.space/wafer-space/%E2%84%B9%EF%B8%8F%20-%20Information/%E2%81%89%EF%B8%8F-questions/what-mimcaps-can-we-use-on-gf180mcu/2026-06/2026-06.json
- Archive source: https://discord.wafer.space/wafer-space/Information/questions/what-mimcaps-can-we-use-on-gf180mcu/2026-06/2026-06.json
**Content**
```text
1.5 fF / um^2 is the config used
```
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---
## message-1511240938616389684
**2026-06-02T05:31:57.265+00:00 — tnt (@246tnt)**
- Message ID: `1511240938616389684`
- Author ID: `596068704471482370`
- Nickname: tnt
- User name: 246tnt
- Type: `Default`
- Discord message: https://discord.com/channels/1361349522684510449/1511221611238522991/1511240938616389684
- Archive source: https://discord.wafer.space/wafer-space/%E2%84%B9%EF%B8%8F%20-%20Information/%E2%81%89%EF%B8%8F-questions/what-mimcaps-can-we-use-on-gf180mcu/2026-06/2026-06.json
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**Content**
```text
This is for a full wafer.space slot right ? Not for tinytapeout ?
```
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---
## message-1511270943996252300
**2026-06-02T07:31:11.105+00:00 — Leo Moser (mole99) (@mole99)**
- Message ID: `1511270943996252300`
- Author ID: `323371864074485771`
- Nickname: Leo Moser (mole99)
- User name: mole99
- Type: `Default`
- Edited: 2026-06-02T07:31:55.046+00:00
- Discord message: https://discord.com/channels/1361349522684510449/1511221611238522991/1511270943996252300
- Archive source: https://discord.wafer.space/wafer-space/%E2%84%B9%EF%B8%8F%20-%20Information/%E2%81%89%EF%B8%8F-questions/what-mimcaps-can-we-use-on-gf180mcu/2026-06/2026-06.json
- Archive source: https://discord.wafer.space/wafer-space/Information/questions/what-mimcaps-can-we-use-on-gf180mcu/2026-06/2026-06.json
**Content**
```text
Stackup can be found here: https://gf180mcu-pdk.readthedocs.io/en/latest/analog/layout/inter_specs/inter_specs_3_43.html
(Sorry, already linked above).
```
**Reactions**
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---
## message-1511484444865855708
**2026-06-02T21:39:33.679+00:00 — were491 (@were491.)**
- Message ID: `1511484444865855708`
- Author ID: `325334453213986816`
- Nickname: were491
- User name: were491.
- Type: `Reply`
- Edited: 2026-06-02T21:40:40.814+00:00
- Discord message: https://discord.com/channels/1361349522684510449/1511221611238522991/1511484444865855708
- Archive source: https://discord.wafer.space/wafer-space/%E2%84%B9%EF%B8%8F%20-%20Information/%E2%81%89%EF%B8%8F-questions/what-mimcaps-can-we-use-on-gf180mcu/2026-06/2026-06.json
- Archive source: https://discord.wafer.space/wafer-space/Information/questions/what-mimcaps-can-we-use-on-gf180mcu/2026-06/2026-06.json
**Reply/reference**
- https://discord.com/channels/1361349522684510449/1511221611238522991/1511240938616389684
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**Content**
```text
it's half height on wafer.space. it's not tinytapeout
tbqh, i have a hard time finding the specific options chosen by wafer.space for gf180mcu, is there a more organized doc anywhere that lists all details of the specific configuration?
```
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## message-1511486460354629892
**2026-06-02T21:47:34.209+00:00 — tnt (@246tnt)**
- Message ID: `1511486460354629892`
- Author ID: `596068704471482370`
- Nickname: tnt
- User name: 246tnt
- Type: `Default`
- Discord message: https://discord.com/channels/1361349522684510449/1511221611238522991/1511486460354629892
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**Content**
```text
Like what ?
```
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## message-1511486696838135900
**2026-06-02T21:48:30.591+00:00 — tnt (@246tnt)**
- Message ID: `1511486696838135900`
- Author ID: `596068704471482370`
- Nickname: tnt
- User name: 246tnt
- Type: `Default`
- Discord message: https://discord.com/channels/1361349522684510449/1511221611238522991/1511486696838135900
- Archive source: https://discord.wafer.space/wafer-space/%E2%84%B9%EF%B8%8F%20-%20Information/%E2%81%89%EF%B8%8F-questions/what-mimcaps-can-we-use-on-gf180mcu/2026-06/2026-06.json
- Archive source: https://discord.wafer.space/wafer-space/Information/questions/what-mimcaps-can-we-use-on-gf180mcu/2026-06/2026-06.json
**Content**
```text
The PDK itself `gf180mcuD` variant will show most details when looking in the tech files.
```
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## message-1511510217668558878
**2026-06-02T23:21:58.394+00:00 — were491 (@were491.)**
- Message ID: `1511510217668558878`
- Author ID: `325334453213986816`
- Nickname: were491
- User name: were491.
- Type: `Default`
- Discord message: https://discord.com/channels/1361349522684510449/1511221611238522991/1511510217668558878
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**Content**
```text
does that mention (for examples) which mimcap config is used and that the ppolyf_u_high_Rs is 1k? i could just have not read them properly
```
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## message-1511616321790541896
**2026-06-03T06:23:35.588+00:00 — Leo Moser (mole99) (@mole99)**
- Message ID: `1511616321790541896`
- Author ID: `323371864074485771`
- Nickname: Leo Moser (mole99)
- User name: mole99
- Type: `Default`
- Edited: 2026-06-03T06:23:42.874+00:00
- Discord message: https://discord.com/channels/1361349522684510449/1511221611238522991/1511616321790541896
- Archive source: https://discord.wafer.space/wafer-space/%E2%84%B9%EF%B8%8F%20-%20Information/%E2%81%89%EF%B8%8F-questions/what-mimcaps-can-we-use-on-gf180mcu/2026-06/2026-06.json
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**Content**
```text
For now, the best way to get that information is to read the magic techfile for gf180mcuD.
> **Note that there are multiple mutually exclusive process options for the
> high sheet rho resistor and MiM capacitor. This tech file assumes the
> options 1kOhm/sq for the resistor and 2fF/um for the MiM capacitor.
However, this is a surprise to me, since I would have expected 1.5fF/um2 or 1.0fF/um2.
The device is called cap_mim_2f0_m4m5_noshield, which would also suggest 2fF, but I don't even see that option the in the stackup?
The only place I can find 2.0fF in the documentation is on this page, which shows strange model names for the MIM caps: https://gf180mcu-pdk.readthedocs.io/en/latest/analog/model_parameters/LV/LV_1_4_6.html
It seems to incorrectly use the model names from the MOSCAP models: https://gf180mcu-pdk.readthedocs.io/en/latest/analog/model_parameters/LV/LV_1_4_5.html
@Tim Edwards do you have any idea what's going on here?
```
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---
## message-1511619982533070919
**2026-06-03T06:38:08.377+00:00 — tnt (@246tnt)**
- Message ID: `1511619982533070919`
- Author ID: `596068704471482370`
- Nickname: tnt
- User name: 246tnt
- Type: `Default`
- Discord message: https://discord.com/channels/1361349522684510449/1511221611238522991/1511619982533070919
- Archive source: https://discord.wafer.space/wafer-space/%E2%84%B9%EF%B8%8F%20-%20Information/%E2%81%89%EF%B8%8F-questions/what-mimcaps-can-we-use-on-gf180mcu/2026-06/2026-06.json
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**Content**
```text
@Leo Moser (mole99) Interestingly I was seeing that in the E-Test results. The test result is named "MIM15_A" suggesting 1.5fF/um^2 but then the spec is 1.7 fF/um^2 minumum and 2.3 fF/um^2 maximum and we hit 1.92 fF/um^2 on run 1.
```
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---
## message-1511624112886517772
**2026-06-03T06:54:33.13+00:00 — Leo Moser (mole99) (@mole99)**
- Message ID: `1511624112886517772`
- Author ID: `323371864074485771`
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- User name: mole99
- Type: `Reply`
- Discord message: https://discord.com/channels/1361349522684510449/1511221611238522991/1511624112886517772
- Archive source: https://discord.wafer.space/wafer-space/%E2%84%B9%EF%B8%8F%20-%20Information/%E2%81%89%EF%B8%8F-questions/what-mimcaps-can-we-use-on-gf180mcu/2026-06/2026-06.json
- Archive source: https://discord.wafer.space/wafer-space/Information/questions/what-mimcaps-can-we-use-on-gf180mcu/2026-06/2026-06.json
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- https://discord.com/channels/1361349522684510449/1511221611238522991/1511619982533070919
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```text
That is indeed strange. I would also have expected "B" in the name, not "A".
```
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---
## message-1511633342729158726
**2026-06-03T07:31:13.696+00:00 — tnt (@246tnt)**
- Message ID: `1511633342729158726`
- Author ID: `596068704471482370`
- Nickname: tnt
- User name: 246tnt
- Type: `Default`
- Discord message: https://discord.com/channels/1361349522684510449/1511221611238522991/1511633342729158726
- Archive source: https://discord.wafer.space/wafer-space/%E2%84%B9%EF%B8%8F%20-%20Information/%E2%81%89%EF%B8%8F-questions/what-mimcaps-can-we-use-on-gf180mcu/2026-06/2026-06.json
- Archive source: https://discord.wafer.space/wafer-space/Information/questions/what-mimcaps-can-we-use-on-gf180mcu/2026-06/2026-06.json
**Content**
```text
@Leo Moser (mole99) Looking at https://mithro-gf180mcu-pdk.readthedocs.io/en/latest/analog/spice/elec_specs/elec_specs_6_4.html
```
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---
## message-1511634760395395072
**2026-06-03T07:36:51.694+00:00 — tnt (@246tnt)**
- Message ID: `1511634760395395072`
- Author ID: `596068704471482370`
- Nickname: tnt
- User name: 246tnt
- Type: `Default`
- Discord message: https://discord.com/channels/1361349522684510449/1511221611238522991/1511634760395395072
- Archive source: https://discord.wafer.space/wafer-space/%E2%84%B9%EF%B8%8F%20-%20Information/%E2%81%89%EF%B8%8F-questions/what-mimcaps-can-we-use-on-gf180mcu/2026-06/2026-06.json
- Archive source: https://discord.wafer.space/wafer-space/Information/questions/what-mimcaps-can-we-use-on-gf180mcu/2026-06/2026-06.json
**Content**
```text
I think there are two orthogonal options. Where the cap is in the metal and what thickness of dielecric.
```
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---
## message-1511635089875009537
**2026-06-03T07:38:10.248+00:00 — tnt (@246tnt)**
- Message ID: `1511635089875009537`
- Author ID: `596068704471482370`
- Nickname: tnt
- User name: 246tnt
- Type: `Default`
- Discord message: https://discord.com/channels/1361349522684510449/1511221611238522991/1511635089875009537
- Archive source: https://discord.wafer.space/wafer-space/%E2%84%B9%EF%B8%8F%20-%20Information/%E2%81%89%EF%B8%8F-questions/what-mimcaps-can-we-use-on-gf180mcu/2026-06/2026-06.json
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**Content**
```text
So the "A" in tha test might refer to option `a` on that page which is indeed 1.5 f/F.
Now why doesn't that match the option we think we have and the min/max value ... I'm starting to think the labels have been cut or only reflect the first option or somethign which would also explain why the label mention 9K top metal while we should have 11 K one.
```
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---
## message-1511726414225739927
**2026-06-03T13:41:03.67+00:00 — Tim Edwards (@rtimothyedwards_19428)**
- Message ID: `1511726414225739927`
- Author ID: `1365118310701600900`
- Nickname: Tim Edwards
- User name: rtimothyedwards_19428
- Type: `Default`
- Edited: 2026-06-03T13:41:32.786+00:00
- Discord message: https://discord.com/channels/1361349522684510449/1511221611238522991/1511726414225739927
- Archive source: https://discord.wafer.space/wafer-space/%E2%84%B9%EF%B8%8F%20-%20Information/%E2%81%89%EF%B8%8F-questions/what-mimcaps-can-we-use-on-gf180mcu/2026-06/2026-06.json
- Archive source: https://discord.wafer.space/wafer-space/Information/questions/what-mimcaps-can-we-use-on-gf180mcu/2026-06/2026-06.json
**Content**
```text
The choice of MiM capacitance and the choice of poly high sheet rho resistance is entirely by process option, and there is *no* indication in the way of layer ID markers to indicate which option is which, or to prevent the end user from designing to the wrong option and then submitting the design. It is entirely up to everyone involved to be on the same page, which is honestly a bit scary. This is why I have in the magic tech file the comment about "this tech file assumes the options. . .". There is literally no other way to convey that information. The only other place it's decided is when Wafer Space submits the form to GF.
I expect that the E-test structures are just named the same thing without regard to the actual options chosen, which probably works better with the automation doing the testing.
The actual options chosen are a bit arbitrary; I made those choices in deciding what options Efabless would use for the Google/GF shuttle run. My intent was to try to get the same MiM cap density as the double MiM structure on sky130. In retrospect, the sky130 res_xhigh (2kohms/square) is used much more often than the res_high and would probably have been a better choice.
```
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---
## message-1511838470572736624
**2026-06-03T21:06:19.985+00:00 — were491 (@were491.)**
- Message ID: `1511838470572736624`
- Author ID: `325334453213986816`
- Nickname: were491
- User name: were491.
- Type: `Reply`
- Discord message: https://discord.com/channels/1361349522684510449/1511221611238522991/1511838470572736624
- Archive source: https://discord.wafer.space/wafer-space/%E2%84%B9%EF%B8%8F%20-%20Information/%E2%81%89%EF%B8%8F-questions/what-mimcaps-can-we-use-on-gf180mcu/2026-06/2026-06.json
- Archive source: https://discord.wafer.space/wafer-space/Information/questions/what-mimcaps-can-we-use-on-gf180mcu/2026-06/2026-06.json
**Reply/reference**
- https://discord.com/channels/1361349522684510449/1511221611238522991/1511616321790541896
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```text
Thanks, I totally missed that scrolling through/grepping for things I thought would match. Based on the defined subckts from `gf180mcuD/libs.tech/ngspice/sm141064_mim.ngspice` (the path as in IIC-OSIC-TOOLS), it seems the documentation is incorrect here. ('documentation' referring to the stackup page: https://gf180mcu-pdk.readthedocs.io/en/latest/analog/layout/inter_specs/inter_specs_3_43.html)
So, I assume in layout (KLayout) I can use cap_mim with MIM-B and M4-M5 options selected, but expect the final capacitance to be ~2.0fF/um^2 for simulation purposes. Is this correct?
```
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---
## message-1511873729167360142
**2026-06-03T23:26:26.289+00:00 — namibj**
- Message ID: `1511873729167360142`
- Author ID: `262706220073222144`
- Nickname: namibj
- User name: namibj
- Type: `Reply`
- Discord message: https://discord.com/channels/1361349522684510449/1511221611238522991/1511873729167360142
- Archive source: https://discord.wafer.space/wafer-space/%E2%84%B9%EF%B8%8F%20-%20Information/%E2%81%89%EF%B8%8F-questions/what-mimcaps-can-we-use-on-gf180mcu/2026-06/2026-06.json
- Archive source: https://discord.wafer.space/wafer-space/Information/questions/what-mimcaps-can-we-use-on-gf180mcu/2026-06/2026-06.json
**Reply/reference**
- https://discord.com/channels/1361349522684510449/1511221611238522991/1511726414225739927
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Once I have PCells for the R-4R (or possibly closer to R-3R; it will depend on yield target and demands on output impedance/how-buffered the output is; e.g. current-mode feeds a virtual ground instead of directly the load) DAC and some replica-bias based MCML logic gates, I'd happily provide comparisons on performance and area impact of instead instantiating them with different sheet resistor option; ofc. assuming them to be re-tuned to make the most of the different option.
I.e., comparing 1000 Ω/□ vs. 2000 Ω/□ vs. 3000 Ω/□ noting the 3k option has +-25% while the two other have just +-20% (at leas tso listed in the PDK).
Regarding the lower-density MIM-cap options, I don't think they are necessarily worth it for the rather low-voltage optimized things that seem to mostly be done on wafer.space; the 1.5fF/um^2 option is rated to 10V and the 1fF/um^2 even to 20V, vs. the 2fF/um^2's 6.6V and the just 10V LD[N,P]MOS devices we have and the somehwat limiting 10~14V breakdown voltage of the Nwell/Psubstrate junction.
```
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---
## message-1512711120056750110
**2026-06-06T06:53:55.835+00:00 — Tim 'mithro' Ansell (@mithro_)**
- Message ID: `1512711120056750110`
- Author ID: `169786952432746498`
- Nickname: Tim 'mithro' Ansell
- User name: mithro_
- Type: `Default`
- Discord message: https://discord.com/channels/1361349522684510449/1511221611238522991/1512711120056750110
- Archive source: https://discord.wafer.space/wafer-space/%E2%84%B9%EF%B8%8F%20-%20Information/%E2%81%89%EF%B8%8F-questions/what-mimcaps-can-we-use-on-gf180mcu/2026-06/2026-06.json
- Archive source: https://discord.wafer.space/wafer-space/Information/questions/what-mimcaps-can-we-use-on-gf180mcu/2026-06/2026-06.json
**Content**
```text
I wonder how we can make this clearer and where to document this?
```
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---
## message-1512712326745423975
**2026-06-06T06:58:43.532+00:00 — tnt (@246tnt)**
- Message ID: `1512712326745423975`
- Author ID: `596068704471482370`
- Nickname: tnt
- User name: 246tnt
- Type: `Default`
- Edited: 2026-06-06T06:58:49.246+00:00
- Discord message: https://discord.com/channels/1361349522684510449/1511221611238522991/1512712326745423975
- Archive source: https://discord.wafer.space/wafer-space/%E2%84%B9%EF%B8%8F%20-%20Information/%E2%81%89%EF%B8%8F-questions/what-mimcaps-can-we-use-on-gf180mcu/2026-06/2026-06.json
- Archive source: https://discord.wafer.space/wafer-space/Information/questions/what-mimcaps-can-we-use-on-gf180mcu/2026-06/2026-06.json
**Content**
```text
Some "process options" details on https://wafer.space/technology.html to specify :
- `gf180mcuD` variant
- Link to the stackup page
- Specify MIM option is 2fF/um^2 and High Res is 1k/sq
```
**Embeds**
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